How to Replace Your Own Furnace

Egads! This is the furnace that came with an old Victorian house I'm currently helping some friends renovate.

Egads! This is the furnace that came with an old Victorian house I’m currently helping some friends renovate.

It seems that every house I’ve ever owned has needed a new furnace. I mean sure, the old furnace was still there clunking along and producing heat, but it was always some embarrassingly old thing installed by someone that obviously didn’t care about energy efficiency (or it predated the invention of efficient furnaces entirely).

But like all owners of these same houses before me, I let it slide and let projects that seemed more urgent on the surface suck up my time.

I renovated kitchens and bathrooms or replaced roofs. It was financially easy to justify the procrastination as well: heating bills for a typical house are under $1000 per year in my area, but if you hire out the installation of a new furnace you’re looking at about five grand (sometimes even $10,000 or more if you are getting a new A/C unit at the same time!)

And sure, the new furnace will be more efficient than your old one. But even if you could find one that ran on free magic unicorn dust you would have a six year payback and more realistically it will take decades.

So I let the slow leakage continue and always felt a small hole in my heart every time that machine kicked on, because for Mr. Money Mustache, energy efficiency is a moral issue even more than it is a financial one.

I figured the numbers would work out much better if I could actually do the replacement job myself, because a top-of-the-line gas furnace only costs about $1500 online these days.  But I didn’t know exactly how to do it and there never seemed to be a good time to learn*. Nobody I knew had ever replaced their own furnace, and the building materials stores don’t even sell them – everybody says you need to hire a pro for such a thing.

But finally, here in the year 2015 and at the embarrassingly late age of 41, I have finally studied up on the necessary tricks, successfully installed two beautiful high-efficiency gas furnaces alongside friends, and am here to tell you it is a perfectly reasonable do-it-yourself project after all**. So let’s get started.

Step 1: How the hell does a furnace work?

When you get right down to it, a gas furnace is just a box-shaped heater connected to some tubes. These days, they have added more internal complexity to make them more efficient, but all you really need to know as the installer is this: Cold Air in, Warm air out, Gas and Electricity in, Combustion air In and Out. It gets even easier if you write these same things on a picture of a box (aka furnace).

Figure 1: Furnaces are Simple

Figure 1: Furnaces are Simple

Step 2: What kind do I need and where do I buy it?

In general, you’ll want a high-efficiency (94% or higher) condensing furnace, with variable speed blower and roughly the same overall heating capacity as the one you’re replacing. It can be smaller in physical size (they have shrunk nicely over the years), but probably not much bigger since you have to fit it into the same space.

Actually finding a place that sells furnaces can be tricky. Like plumbing was a few decades ago, the heating and cooling industry is still an insider’s game, with low-profile stores that only sell to contractors, and contractors that insist their field is far too dangerous and exacting for any homeowner to master. If your personality type is at all similar to mine, the very words “consult a qualified installer” piss you off a little and make you want to learn the trade.

Typing “where to buy a gas furnace” into Google leads to a mixed bag you can sift through, but I ended up finding the best results for my situation at a place called Alpine Home Air.
(Update: nowadays you can even get these things from Amazon – with free shipping!)
Specifically, for both recent installs, my friends just went for the top-of-the-line Goodman 96% unit.

For a bit more background reading on the field, Consumer Reports has a free furnace buying guide.

Step 3: OK, Got The Furnace. What Other Parts Do I Need?

Remembering that diagram above, you’re hooking up air, gas, intake, exhaust, and electricity. Everything will be available at your local building materials shop, with the possible exception of a condensate pump.

If you’re installing the furnace from scratch or replacing a Crazy Spaghetti Octopus monster and want to re-do the ducting in your basement completely, you might also pick up:

  • a return air box : this is just a big sheet metal box that you set your furnace on. It serves as a big air scoop where you can connect all your return air ducts, and it also has a convenient slot to hold the air filter.
  • a supply air plenum to handle the heated air on its way out. You’ll cut holes in this to connect supply ducts to the rest of your house.

Step 4: Let’s Hook This Sucker Up

Read the Manual:

Somebody actually cared when they wrote this instruction manual.

Somebody actually cared when they wrote this instruction manual.

I was pleasantly surprised to find that the Goodman furnace we used came with a fully detailed installation manual – none of this consumer-oriented “run screaming and consult a professional” attitude. Every hookup and specification, right down to how far to keep your vent pipes away from exterior windows, was described clearly with pictures. I spent a leisurely hour at home reading it from cover to cover the night before beginning the installation, which allowed me to have the big picture in mind on the big day.

Household Air:

custom_supply_boxCool air (also called ‘return air’) gets sucked in through the bottom of the furnace, heated, and blown out the top (‘supply’). If you are replacing an existing furnace, you just need to carefully extract the old furnace from the big metal boxes, then seal the new unit to the same boxes. You can reshape or extend them as necessary.

If you have central air conditioning, there will be a separate metal box stuck in with everything else. Just leave it in place, be careful not to break the tubes and wires, and it will continue to work with your new setup.

Tools and tips: You cut the metal with tin snips or a grinder with metal cutoff wheel. Fold pieces nicely with a metal brake. Screw things together with sheet metal screws. Create airtight and heat-resistant joints with silver foil tape (not duct tape). Brush on duct sealant to all potential air joints to create a better seal. And above all, instantly master sheet metal duct work with a few YouTube videos on the subject.

Combustion Air and Exhaust:

pvcHere we are just running two pieces of 3″ PVC pipe (you can even use 2″ for shorter runs) from the furnace to an inconspicuous place on the outside of your house. It’s a fun design puzzle, deciding how to route the pipe and figuring out which fittings to use to accomplish it. Your goal is a classy looking job. You cut it with a miter saw or sawzall, and glue it with purple PVC primer and PVC glue. Again, watch a few videos if you need to learn how to handle this stuff.

As a huge bonus, these same plastic piping skills will allow you to run drain pipes, which lets you build your own bathroom from scratch (future article?)

Gas Supply:


My friend Mike uses a pipe wrench to twist on a length of black pipe.

Although people tend to be afraid of working on gas piping (after all, you can blow up your entire house if you get just the perfect gas leak and ignite it), it is easier than ever and quite rewarding to do yourself.

An existing furnace will already have a gas line, complete with shutoff. So in most cases, you can just connect your new furnace with a standard flexible gas connector.

But if you need to change the routing, you can turn off  your gas supply at the outside meter, use a big pipe wrench to unthread the existing black gas pipe, and buy new lengths and fittings at the store to create your new layout. They will even custom-cut and thread the pipe for you, or you can do it yourself if you own a pipe threading tool. Once you have the right pieces, wrench everything together with plenty of pipe thread sealant (aka “pipe dope”) to create gas-tight joints.

Three pieces of CSST come together at one traditional T-joint, where we split off a branch to feed the existing water heater.

Three pieces of CSST come together at one traditional T-joint, where we split off a branch to feed the existing water heater.

These days, I usually bypass the black gas pipe entirely and use the newer flexible Corrugated Stainless Steel Tubing (CSST for short) instead. This saves time and allows you to thread the tubing right through joists and around corners, keeping it out of sight – especially useful if you’re installing in basement that may eventually be finished. The fittings come with detailed instructions and you can of course watch videos on CSST installation as well.

When everything looks perfect, you turn on the gas and check thoroughly for leaks with a soap solution, your nose, and a gas leak detector.


The furnace uses electricity to run its control electronics, igniter, and blower. But you just need to connect it to one normal (15 amp) household circuit. Black wire is hot, white is neutral, and green/copper is ground. You make the connection right inside the junction box built into the furnace, although you’ll want to mount a switch somewhere in the circuit so you can power down the furnace.

Another option (if your inspector allows it) is to wire on a cord and simply plug the furnace into a nearby electrical outlet. This is simpler, and allows you to plug the furnace into a backup power source (generator or large battery) to restore heating in the event of a power failure.

Condensate (aka dripping water):

When an efficient furnace runs, it condenses some water out of the hot combustion gases. This drips slowly out of the furnace through a little plastic spout, and you need to connect that to a flexible plastic tube that takes the water somewhere safe. If you have a floor drain in the basement, pipe the water there. If you need to lift the water higher, you dump it into a condensate pump, and have the output go to a nearby plumbing drain.

Thermostat wiring:

You are down to the really easy stuff now! You can follow the instructions for the furnace and thermostat, but in my case I just connected the red, green, yellow and white wires on both sides.  For a longer explanation of what the wires do, here’s a guide.

If you’re looking to upgrade your thermostat at the same time, I am a fan of the Ecobee Lite Wi-Fi enabled thermostat. It is reasonably priced but also has a beautiful physical form, and a really nice, robust user interface (and phone app). The default operation is ridiculously simple, but you can also dig in and adjust lots of detailed settings if you are an engineer like me.

And You’re Done!

It’ll take some work and you will learn a few things, but at the end of the project you’ll have a beautiful new furnace that provides a sizable return on your investment of time and money.

Here’s a picture of one of the finished installations at a friend’s house. From bottom to top, notice the custom return plenum, furnace, existing A/C box, PVC combustion air piping, and my homemade supply plenum that funnels the air to the old ductwork.



Successful DIY mentality


Two local friends exchange witty banter even as they build custom ductwork for a current project house. This was a bigger job as the original 1910 house had no real ducting at all – we had to open up walls and run pipes to every room in the house. Your furnace upgrade will be easier.

When I first started do-it-yourself home renovation, at least part of the motivation was a desire to save some serious money. But in recent years the need to conserve money has faded away completely and yet I find myself more enthusiastic about building and fixing stuff than ever. This is because learning new skills, solving puzzles and creating finished products you can be proud of is not just something you do for money – it’s the purpose of life itself.

So when confronted with a choice between fixing something yourself and hiring it out, you do well if you push your comfort zone just little a bit further each time. Just remember the mantra: “This is possible, and plenty of people with fewer advantages than me have accomplished the same thing many times in the past”

Then you get to work, read the instructions, tinker, make mistakes, learn, and succeed. And continue to build on that success, forever.

Further Reading: You can find many more of my DIY-Themed Articles with the shortcut https://www.mrmoneymustache.com/tag/diy/

* When I bought my current house I ditched the hot air furnace entirely and built an under-floor radiant heat system instead. Now into its second winter, we are still loving it.

**Do you need a permit and Inspection? 
In general, yes – replacing a furnace is something your city wants you to get a permit for. But it’s not a big deal – going through this process is a nice low-cost safety check to make sure you get the details right. And having an inspected, approved permit on file will make it easier to sell your house further down the road.

  • Mike November 23, 2015, 4:41 pm

    I always wondered why HVAC was never seen as something the consumer could do. This is a fantastic write up, thank you for sharing! The source to find parts is very helpful.
    Years ago my a/c went out. Had a few companies come give quotes ranging from $700 – $1100 and explain the issue. I went to the store purchased $22 worth of wire, proceeded to replace and it still works today!

    • Jim Wang November 24, 2015, 6:24 am

      It’s because there’s a lot of money to be made for professionals. All of these systems are simple but you start throwing weird names to parts and then build up a culture of ignorance (be careful you could blow up your house!) and now you have homeowners turning to professionals for simple repairs. That’s why so many people think these guys are crooks. It’s not that they’re ripping you off, it’s that you aren’t knowledgeable enough to buy the $22 worth of wire and do it yourself.

      Also, they do provide value. One phone call and your heating problems are solved (hopefully). Some people have the means where they honestly don’t care about the cost, they want the heat and they’re happy to overpay.

      • Joe the Plumber February 24, 2019, 6:35 pm

        Come on now. The only reason guys like me make money on things like this is because the vast majority of people either don’t want to know about it, or don’t want to do it. And closed industry? Maybe things have changed, but last I checked this has all been free info in the internet.. or maybe MMM just has a bone to pick. I think it’s great for homeowners to know how their mechanical systems work, and how to repair and keep them maintained. It would be like saying, “don’t learn about nutrition, only eat what your doctor says.” Of course you should learn all you can.

        Oh and make sure that gas line is tight. You don’t want to blow up your house ;)

        • Isaac December 22, 2022, 8:39 pm

          I just tried buying a furnace from a couple local suppliers. Both told me they couldn’t sell to me either because of warranty or insurance issues. Found the same furnace on Amazon for $100 less and had it delivered 2 days later….

          • Mr. Money Mustache December 25, 2022, 8:11 am

            Yeah, Amazon is really becoming more of a gold mine for us home builders/improvers every year.

            Long ago I read a book called “Built to Last” about the history of Home Depot in its days as a scrappy startup in 1978. Back then, even more of the home improvement world was hidden from homeowners – locked in proprietary stores that only sold to professionals. They had to battle a lot of entrenched interests to let Joe Homeowner buy and install his own light fixtures or tiles or kitchen faucet. But now the world is a much better place for the change.

    • Dennis Trump January 23, 2017, 11:06 am

      Mike, thanks for your article on furnace instalation. I am a homeowner that believes that I should know about everything involved in the maintenance of my home. Other than the money saved in doing this work myself. I have learned a lot over the years in doing my own work when I need to. I have installed one furnace and am now in process of a second. This in a different location with some new challenges to overcome. I have personally experienced the attitude of the installer. The threats that my ignorance will no doubt cause some sort of explosion. I have had trouble getting parts for the same reason. But can’t even get a service person to come and install parts on my furnace because I didn’t purchase it from him. They are always willing to sell me a new furnace, then they will install it for me. Just trying to get a proper conversion kit to use propane in my furnace almost ended up in failure simply because the industry try’s so hard to keep scaring us that we will blow ourselves up if we try doing anything for ourselves. It has literally taken me 3 months to sift through the information available mostly on line to get to where I am now finally having a propane provider setup a tank of propane for my furnace in just a couple of days. Shortly after that I will do the conversion and heat my frozen shop.

  • Kyle November 23, 2015, 4:47 pm

    Just added $400 worth of blown in insulation a week ago which was a lot easier than I expected and the 30 year old furnace has been on my mind since I bought the house. It is a planned DIY project in the future. I appreciate that fine looking attention to detail on the finished project, I don’t think most professional work looks that good!

  • Ray Austin November 23, 2015, 4:48 pm

    There is a good reason why manufacturer’s require contractors to be licensed. If you read the manual really well you would have noticed your nice new furnace now has no manufacturer warranty if something goes wrong with it. In all reality you may not find anyone willing to work on it if they suspect it was installed by a home owner.

    Liability reasons: carbon monoxide is a colorless, odorless gas that make house occupants sick initially. This sickness mimics flu symptoms. Which makes it hard to determine whether it’s the flu or something more sinister. Furnaces don’t create carbon monoxide under normal conditions, in most cases it is produced because there is not enough combustion air or the flue pipe is not right (improper combustion). Back drafts among many other complex scenarios could give you a recipe for disaster.

    What is your life worth?

    I am a licensed HVAC contractor in Texas.

    • Mr. Money Mustache November 23, 2015, 5:18 pm

      Yup, exactly the attitude I usually get from my fellow licensed contractors.

      This is a CANCER in the culture of our trade – criticizing the work and the ideas of others. It has happened with every DIY article and on every jobsite I have ever experienced.

      Lighten up, brothers! Why not devote your time to helping people and sharing your advanced knowledge rather than trying to scare them away from learning new things?

      For example, if Carbon Monoxide were really a concern*, why not suggest how to test the finished system with a CO monitor? And provide a link to where we can buy or borrow one at a reasonable price?

      I also really enjoyed the scary criticism that came up when I wrote the article about my hydronic heating system a couple years ago. It turned out to be 95% bullshit but I did get a couple of useful design improvements out of the discussion as well: http://forum.heatinghelp.com/discussion/149762/how-prevalent-is-this

      *which it isn’t in a power-vented installation like the one I show in this article. It’s nearly foolproof, getting plenty of intake air and exhaust venting, if you use 3″ PVC and route it cleanly.

      • RLepage November 23, 2015, 7:09 pm

        There are usually times when you want to have a professional do work: things like doctors, pilots, or engineers. While HVAC installation is not something that requires a decade worth of specialized training, there are some instances where it can be a problem if your installation is deficient.
        For instance, the combustion supply and exhaust lines leading to the furnace have to be made of PVC because the condensate is actually diluted sulfuric acid. If someone were to decide to install non-stainless steel combustion ducting (maybe they were frugal and thought to use extra interior metal ducting) it will eventually corrode through and then you’ll be power venting combustion by-products into your home.
        My suggestion is to consider having a certified or experienced person to just double check your work. That way you some certainty and you’re not caught with a mistake about something you didn’t know you didn’t know.
        Good luck!

        • CCC November 24, 2015, 7:13 am

          “My suggestion is to consider having a certified or experienced person to just double check your work.”

          That is the entire point of the local building inspector’s permitting process. Assuming your local officials are competent, by pulling a permit you will ensure that the system is inspected by a qualified professional who will not sign off unless it is properly installed. Sure there is a small risk the inspector will miss something, but the same risk exists that a “professional” will miss an important detail.

          • RLepage November 24, 2015, 9:43 am

            There’s variation in protocols between different AHJs. In some cities in BC, despite pulling a permit for work, this does not guarantee that an inspector will review the work. They usually assume that the work is done by a competent and trained individual and have therefore deem the work compliant. Depends on what kind of work is being done, by whom, and under which jurisdiction. Caveat emptor.

        • Fred Jenkins November 29, 2015, 12:02 pm

          That’s basically what I did.

          Installed myself, paid a contractor $100 to come and look it over. He pointed out two things which I fixed and haven’t had a problem since.

          Better than spending the $22,000 I was quoted. $10,000+ above cost for less than a weeks work.

        • Dylan Mcgraw May 6, 2020, 5:43 am

          That was a good point. Just after the installation have a contractor come out to finish the last 10% of the job. Just read the instructions install everything the right way, pay attention to what your doing. Google and YouTube is great! Then after you finished your part the contractor will come and inspect all the areas you hooked up and then complete the installation. Its really that simple guys and girls, plus anything that you dont feel comfortable doing yourself just tell your contractor to do it for you. Its a great way to save money and learn something. Im proud to be an American where atleast i know im free!!

      • DAnny November 23, 2015, 9:36 pm

        Based on my experience, sometimes the professionals do really sub-par work. Issues that I’ve had with HVAC installers (and auto mechanics) directly led to me becoming more of a DIYer (along with some inspiration from MMM). I find that sometimes these professionals are just looking to finish the job, and maybe quality isn’t so much of a concern. Even if I’m not a professional, if I’m working on my own home or car you better believe I’m going to put in the time and research to be sure I’m doing a good job.

        • Mike S November 30, 2015, 10:55 am

          Agree with this.

          Ray Austin wrote: “What is your life worth?” It’s worth way more to me than the “pro” whose trying to maximize throughput.

          If you’re competent and careful, DIY is the way to go. It will take me longer than the professional, but (at least in most things) I’ll end up doing a better job because I’m more interested in the quality than the time.

        • Donna December 20, 2015, 11:58 pm

          I do as many of my own home and car repairs as possible. If I had a garage to work out in; I would do a lot more. Luckily, when absolutely necessary, I am able to diagnose the car and have a reliable, low-cost place to send it. Paying the going rate for shop rate and the mark-up on parts is unacceptable to me.

          Although I currently rent my house, I also do many repairs myself then deduct any expenses from my rent. Big jobs, I let the home owner handle only because it is not my home. I do have the knowledge to build/replace privacy fences, replace hot water heaters, etc.

          Being a lady and being told that I can’t do something or could never do such a job only means that I will get it done.

      • Jim Wang November 24, 2015, 6:26 am

        If licensed contractors really “cared” then they’d offer post-installation inspection services… but they don’t. :)

        • Dan November 24, 2015, 4:05 pm

          At least in the US, contractors are probably WAY too scared of the liability issues to want to mess around with approving work performed by someone else.

          • Bill November 24, 2015, 4:45 pm

            People need to stop going to law school. Seriously. That’s the real cancer here. There are far too many lawyers, as even my lawyer sister will finally admit. At my brother’s law-school graduation (I told you there were too many), the speaker told them about all the fine career opportunities they had opened for themselves, like writing about law, blogging about law, mediation, anything but practicing law.

            • Dan November 25, 2015, 6:49 am

              I think it’s more complicated than that. There are too many lawyers in some areas, and too few in others. This is why you can hire a personal injury lawyer for very little (or even contingent fees) whereas hiring a competent patent lawyer is going to run you $200/hr minimum. I think this fits with the theme of the article, which sums up as follows: development of /useful/ skills is good.

            • Bill December 1, 2015, 8:51 am

              Well, yes, patent law. So get an engineering degree *and* a law degree.

      • JJ November 24, 2015, 7:58 pm

        If you are going to mess with Air conditioning coolant you NEED to EPA certified. There are laws governing the release of the coolant and the new R410A fills our newer higher pressure backyard bombs. Every other country but the US doesn’t want it no because of the CFC release but it is a hardcore greenhouse gas. Find a local facility where you can get EPA certified and for god sake keep refrigerant on lockdown. You can usually find a local supplier that sells to the public, but as a bonus with the EPA cert, you can get licensed by your state to work as a refrigerant contractor. I was a service tech for years and the amount of people that just dumped that stuff into the air is horrifying. The high cost of A/C service mostly comes from refrigerant handling (and capacitors…those things cost us 4 bucks yet we charge 80+ bucks a pop to replace.

      • mike November 24, 2015, 10:18 pm

        I’m a heating/ac contractor and when I look at your shower install post, now that looks difficult. Congrats taking the job on Pete. Another satisfaction I get too when I learn something, it’s mine for life, no one can take it away from me.

        Next door neighbor had a cable break on his garage door. $400 later it was fixed. Repairman said the torsion springs were bad too and needed to be changed, but when homeowner left receipt on table of his company changing out the torsion springs a few years before (and under warranty) for some reason they didn’t have to be changed after all.I got so angry watching this, I’m learning how to fix and install garage doors. (I bought 2 garage door cables via Amazon for $.01 plus shipping.)

        If you want a laugh, go to Youtube and watch these yahoos tell you how to repair garage doors but you must use their company. They will tell you how dangerous it is and that it can “kill you”. Of course it can kill you, but please, we live in a world of “be safe, don’t take any chances”. It’s bullshit.

      • Jeff November 26, 2015, 3:40 pm

        There’s no guarantee a professional will do the job properly either.
        An intelligent competent DIY person should always do their own work to ensure the quality is right.

        As for carbon monoxide, firstly do the installation properly. Secondly buy a carbon monoxide alarm. Thirdly check the life of the alarm and set up a google calendar appointment so you remember to replace it (typically in 10 years).

        • Alicia Kennelly October 26, 2017, 10:46 am

          Some states (including my own in Minnesota) require a CO detector on each level (and within so many feet of bedrooms) by code. I have one with a digital readout that I can see at a glance when entering the house through the garage. The others are combination units with smoke alarms.

      • Zach April 14, 2021, 9:42 am

        Thanks for posting this! Just bought a house with a 30 year old furnace and was not very keen on the idea of paying 5 grand for a day of labor. Honestly I was intimidated at first by all of the internet threads of professionals warning of people blowing themselves up. But then again last year I replaced the motor on my car for the whopping cost of 200 bucks plus some new tools after being quoted 8000 to repair it. Aside from calibration (which i would pay for) the installation seems like a fairly easy plug and play system if you have basic mechanical skills and do your due diligence on how piping, pvc, electrical, and ductwork are put together. Hats off!

        • Mr. Money Mustache April 15, 2021, 9:12 am

          Yeah! Man, if you can learn replace the engine in a car, you can definitely learn to do anything in a house (including building one from scratch, and of course inventing your own new type of heating/cooling systems if you like)

          At a basic level, I can see why the contractors are concerned: when I write optimistically about this, they might feel I am discounting the hard work they put into learning and perfecting their trades. And I don’t mean to do that.

          There is true value in being an all-out expert, and you deserve to be paid well for it. For example, I’ve been a pretty serious carpenter for over 30 years now, and I’ve learned all trades related to housebuilding… and it is really starting to show. Stuff just gets done fast, and well. But it doesn’t mean I discourage my friends (or blog readers) from trying to learn it themselves. Yes, they will make mistakes and things will come out crooked and sometimes need to be re-done. But the value to them from going through this learning process is immense. And I like to do my best to try to accelerate their learning process with encouragement and guidance.

    • rae November 23, 2015, 6:43 pm

      Where I live in Canada, it’s actually the law the have CO alarms in your house. Not that I would ever attempt to replace my furnace myself, but I would’ve suggested getting one of those instead of being a whiner. Look on the bright side: anyone in Texas who attempts this and fails to complete can call you to fix it! More business!

      • Nate Merrill December 5, 2015, 4:24 pm

        Half of the states in the USA require CO alarms too, I am new to this website but I think Mr. Money Mustache is from Colorado which is on of the states that require COalarms.

    • FrugalTravelGal November 24, 2015, 2:47 pm

      I jokingly forwarded this to my husband, because we just had our furnace replaced 10 days ago. He was not amused, and he said, “Dumb idea for many reasons, not the least of which is that equipment not installed by a licensed contractor has NO manufacturer’s warranty.”

      MMM, from your “my fellow licensed contractors” comment below – it appears that your DIY furnace installation would not void the warranty. However, I suspect most of your readers aren’t licensed contractors.

      • afox November 24, 2015, 3:02 pm

        ahhh, but there are caveats to what you say. Warranties for items such as furnaces, roof shingles, and other building supplies generally only cover “materials” not costs of installation. With a furnace install (and even more so with shingle replacement) most of the cost is for the labor to install the product. The actual wholesale cost of a furnace to heat a 1,200 sq ft home is less than $2,000. The price to install such a unit would be near $5,000 So you can see why it is easy for the furnace manufactuer to give such a good warranty. The roof shingle warranties always interest me. They are for like 20+ years. The shingles account for 10% of the cost to replace them. Do they adjust for inflation when paying warranties? I think not. The bottom line is that the usefulness of these warranties are marginal.

      • Mr. Money Mustache November 24, 2015, 3:44 pm

        Hey FTG,

        First of all, your husband is probably wrong – DIY rarely voids the warranty, whether it is for a furnace or maintenance on your own brand-new car. One of my friends actually checked specifically with Goodman because he was curious.

        Secondly, making decisions based on warranty coverage is bad math in my opinion. What percentage of your life’s experiences with a warranty service department would you rate as positive and efficient? For me, well below 10%.

        Instead, I focus on owning fewer products in the first place, buying only good ones, and understanding how to install and fix them as much as possible. Even if it ever breaks, I’m way ahead of the person who is dependent on other people to fix the problem for him.

        Cars are a great example: much better to own a 10-year-old reliable car that never breaks, than a 1-year-new fancy car that gets fixed under warranty.

        If something is unfixable or out of warranty, I can have a new one shipped from Amazon the same day, which will probably be better and cheaper than whatever broke.

        • JJ November 24, 2015, 8:01 pm

          If you can find one that sells to public, I highly recommend Armstrong brand. Stainless steel heat exchangers and no bells and whistles. Not as cheap as a goodman but if you want quality, I just did you a favor :)

          • jestjack November 28, 2015, 4:13 am

            Armstrong is a good brand ….I think they are owned by a division of Whirlpool…

          • Alicia Kennelly October 26, 2017, 10:50 am

            Amana is another brand that uses stainless steel heat exchangers. They and Goodman are both made by Daikin (IIRC), but the Amana uses much higher grade components.

            That said, I have had very good experiences with warranty repairs and exchanges when I have needed them.

        • PFI November 25, 2015, 2:17 pm

          I’m in the market for a new furnace so this is of interest to me. I’ve been doing a bunch of research and I get what you’re saying about trading warranty vs fixing things yourself; I’ve even repaired my own furnace a couple of times. But I’m still not sold on DIY installation, it really looks like there’s no warranty for the unit you’ve installed.

          From the Goodman warranty:

          This warranty does not apply to:
          Units that are ordered over the Internet, by telephone, or by
          other electronic means *unless the unit is installed by a dealer*
          adhering to all applicable federal, state, and local codes,
          policies, and licensing requirements.

          Also, you’re a contractor with lots of industry contacts. I have found it can be very tricky for a non-contractor to find a gas guy willing to inspect and certify a home-owner installation, in fact most won’t. My initial research is the few people that will do it, charge hundreds of dollars for the inspection and tag. Also, if you’re doing AC at the same time, in my area you have to pay a certified technician to empty the coolant and then *tag it with his license for disposal*.

          I got a quote for a similar Goodman furnace for 1900 installed.

          If I DIY it’s 950 for the furnace and, so far, about $350 for the inspection. Add about $100 for tools and materials [although for me specifically, probably more since I need to bore a new hole in my brick for the intake], 100 for disposal, and the savings are closer to $400, and I’m giving up the 10 year warranty. YMMV

          I fix pretty much everything else in my house but the inspection and certification steps here seem to be the lynch pin.

          Having said all that, everyone should know how to change their own vent motor and clean their own flame-sensor. Those two things alone can save a ton down the road.

          • Mr. Money Mustache November 25, 2015, 5:39 pm

            Not bad PFI – if everyone could get a $1900 quote for a high quality furnace replacement I would have had less incentive to write this article.

            As for friends in various occupations – yes, definitely worth building up a collection of those!

          • Donald January 28, 2018, 7:45 pm

            I got quoted $8000 for a high efficiency furnace. Local code here in Oakland, CA requires a dedicated fuse on the fuse panel and the ducts pass a leak test and ducts be insulated, so you need to subtract these items from my $8000 quote to compare. My quote is re-using my existing ducts. They are also replacing my supply and return plenum, I assume to pass the leak test.

        • Hvacpro March 8, 2019, 5:22 am

          Goodman is the laughing stock of the HVAC trade. The warranty on them is terrible along with their heat exchangers and components. And yes unlicensed persons can install a furnace with warranty but it does usually cut it down to 5 years instead of 12. I did notice that you didn’t explain how to check your gas pressures so I assume you didn’t do it. I give the furnace about 6 years before a major fault. You bought a Goodman? Goodluck :)

          • Mr. Money Mustache March 8, 2019, 7:58 am

            Hahaha. Thank you HVAC Pro!

            As noted in the article, we get critical professionals around here on all of my articles around electrical, plumbing, and furnace.

            Why are my fellow tradesmen so defensive? If you’re confident and secure about your skills, wouldn’t you want use your knowledge to help other people, rather than criticizing them and making them feel like fools for doing things “wrong”?

            • ReeferMark April 16, 2019, 1:16 pm

              It’s not that we dont want to help the average homeowner DIY. In fact I help people I know all the time with questions, and problems on their home equipment. It’s the fact that unlike your average floor installer, or tile guy, or your cabinet guy, licensed red seal trades go through a heck of a lot of training. It takes many years to get our licenses, and many more years to master the trade they are in. There are many codes when it comes to installation of equipment that aren’t listed in the manufacturer’s instructions. is the average homeowner aware of them? Not likely. Thankfully here in Canada, you have to be licensed to even touch gas piping. You cant just get someone to sign off on your work, and to be honest, I don’t know many guys who would. Our gas license is our livelihood, and as such, writing off on an amateur DIY piping job is not something I will ever do. I will help you, and oversee your work, but that’s it. All I can say is thank God I live in Canada where the laws are more strict and help protect homeowners from doing stupid things like this.

            • Mr. Money Mustache August 31, 2019, 1:14 pm

              A heck of a lot of training? Many years? Statements like this are what make these conversations silly.

              Residential construction – all of it, all trades – is EASY. It’s quick to learn and easy to do right. A clever eighteen year old could master everything in a year or two of full time work, if apprenticing with experts.

              The only part I have found that takes longer is the artful parts – learning how to work around the corner cases when things go wrong (like flaws in the material or restoring an old-crooked house). Becoming a great carpenter in all situations thus takes a few years longer, I think.

              The cool part about all of this is that the trades reinforce each other. If you understand how to build foundations, you will be a better plumber, and vice versa. Understanding structural design and framing and welding and electrical stuff lets you solve problems in a way that a group of the best specialists in those trades would not think of.

              But all of this is to say – no criticism or “good luck” fear-mongering, please. Just encouragement.

    • jestjack November 27, 2015, 2:17 am

      As a landlord the chance of a lawsuit based on a failure is too great for a DIY furnace project. I’m looking for safety that comes with a trained, licensed and bonded tradesman. And todays furnaces are very complicated…not like the “ole days”. Just had an oil furnace fail in a rental unit and the tech had an abundance of electronic gadgets to trouble shoot and fix the unit.

      • Mr. Frugal Toque November 30, 2015, 12:35 pm

        I had a licensed Master Furnace installer guy install my original oil furnace. When I had it cleaned, the oil company red-tagged my oil input spigot (no oil deliveries until I fixed the following):
        – AC coil too close to heating coil]
        – oil pipe slowly leaking
        – oil exhaust too close to several intakes
        – furnace and water heater exhausts too close together.
        – aluminum vents touching copper pipes
        – oil exhaust fan turns off same time as furnace instead of after 30 sec. delay
        – oil exhaust leaking into house (used caulking instead of proper interface)
        How did it pass inspection? Well, as a Master Furnace Whatever, he files for the inspection and they only randomly inspect a sample of his work. When I sought the guy out and demanded he fix his old shoddy work, he had shut down his company and declared himself to be a new company.
        I don’t think there’s anything magical that happens with certification. If you do it yourself and have it inspected, check for leaks, have a CO detector etc., you’re as well off as rolling the dice with a guy you don’t know.

    • JT November 30, 2015, 6:45 pm

      It’s funny, but every contractor I’ve ever hired to work on a property of mine, repeat, EVERY SINGLE ONE, has screwed up something. And that’s just the stuff I’ve caught, because when an installation pings an alarm bell in my engineer brain I pull the relevant codes, read them, and then apply them.

      Yet there’s no shortage of contractors who are happy to perpetuate the complete MYTH that ONLY CONTRACTORS CAN DO WORK OR ELSE YOUR WHOLE FAMILY WILL DIE!

      There’s only one contractor in a hundred that I’d trust to boil water. I think I’ll keep using the internet and critical thinking skills to do work for myself for a fraction of the price.

    • James December 1, 2015, 10:15 pm

      He spent $1200 on the furnace. Even if you’re right about the warranty, the expected cost of a total replacement can’t be more than about a hundred bucks. Nobody would buy from a company with a failure rate above 10%.

      Carbon monoxide alarms exist and are not terribly expensive.

    • David Solberg June 9, 2017, 8:23 am

      I actually like doing things myself because I usually do a BETTER job than the contractor. It’s not because the contractor is a bad person; it’s just that I will spend the time to do a better job because it’s my house. I’ll also research every part of the process so I know I’m doing it right. A contractor might choose equipment that’s not quite as good because that’s all their supplier offers or because it’s just not worth their time. Additionally, I understand my needs (in this case how the rooms get hot and cold in various seasons) better than the contractor, so if I pick out things myself, I can pick up the best thing for my house’s situation.

      I don’t blame them— they have to make a living, and they usually do a good enough job. My point is that I can do a BETTER job simply because it’s my house and I care more.

    • Mike January 16, 2020, 8:45 pm

      When I moved into my house the gas lines in my furnace water heater area were do poorly laid out a gas line running up against the stack on the gas water heater. About 6 feet of unnecessary pipe . I first removed all the extra and dangerously installed pipe. Then I drew up my plan made my measurements and fixed that rats nest created by that local licensed HVAC guy. I am a mechanic by trade and I can say this with a realistic amount of certainly. If you use common sense double check your work and follow the instructions and code a furnace can be a diy job.Although there should be a fair amount of time spent learning the procedures. I can teach a person how to safely change the brakes in thier car in less than an hour. Skilled labor is great when a person has the resources. Frankly my industry and yours have been ripping of the public for decades. Labor charges are to high. Parts are absurdly priced as well. I don’t know the ins and outs of HVAC companies but u can tell you with absolute certainty that the automotive field the owner is screwing everyone involved from the customers to the mechanics. I work in a highly technical field. I revisit school every year to year and a half. That being said more than 50% of my job could easily be done by a novice. I have installed several furnaces and a dozen or so water heaters because the bids for the install was 800 plus the permit cost. That is a disgrace. Just the same as a 1500 brake job.

  • Rob November 23, 2015, 4:52 pm

    Awesome. Thanks for the great write up.

    Not sure how to phrase this question, so I’ll be blunt. But do you find the inspectors in your county to be competent? The ones that ours sends out seem not to care that much/ don’t know a whole lot. Sometimes I wonder if it’s just a money grab by the county…

    • Mr. Money Mustache November 23, 2015, 5:15 pm

      Yeah, Longmont is a bit of a utopia in terms of relatively smart and effective city services. If they were less fun to work with, I’d be less likely to bother with permits.

      Right next door, Boulder has a more tyrannical building department. The inspectors busted in on a minor kitchen model a friend of mine was doing, simply because they saw a dumpster in the front driveway. Nobody had complained or anything like that – they just have a much stronger desire to ENFORCE everything there.

      • David Robarts November 24, 2015, 1:43 pm

        Strictly enforcing the requirement to have building permits and providing competent inspections are two totally differnt roles. Do the Boulder inspectors sign off on shoddy work? If so, then it really is just a money grab. On the other hand if they have inspectors that know what they are doing and demand the job be done right before signing off then making sure all work that should be inspected is inspected is just part of doing a good job.

  • Kat November 23, 2015, 5:09 pm

    I’m having someone look at my furnace this week. You need permits here (in Washington County, Oregon) to do anything, but my furnace is a 20 year old electric monstrocity that is now blowing luke warm air. I can’t decide if I want to spend $400 to fix it or $2200 to replace it.

    • kristen November 24, 2015, 11:24 am

      If it it 20 years old, it probably makes more sense to replace it with a new, efficient version. The initial cost would be $1800 more than the repair, but it is possible that you could quickly recoup that in energy savings and enjoy much lower bills in the future.

    • ohyonghao November 24, 2015, 5:58 pm

      Hello fellow Washington County resident! I think NW Natural might have some incentives with Oregon Energy Trust that can bring the cost down. Of course so far a lot of my experience with these incentives is they require licensed contractors in order to get, though I was able to blow my own insulation. Might be something to check out. If it’s electric I’m sure I saw something from PGE.

      • Chris I November 25, 2015, 10:15 am

        They do, but I believe the rebates require that the unit be installed by a certified installer. With the rebates and tax deductions, it would have been only marginally cheaper to install my own when I did it last year.

    • Noel November 25, 2015, 10:25 am

      I’m assuming that if you have an electric furnace you don’t have natural gas service at your home. If that’s the case I’d recommend replacing it with an air source heat pump. Those regularly run at 2x the efficiency of an electric furnace. The install is more complicated than the gas furnace MMM talks about here, so I’d recommend finding a good HVAC contractor. I haven’t looked into the details, but Energy Trust of Oregon does offer some of the best rebates in the country for these kinds of things as others have suggested.

    • jestjack November 27, 2015, 2:22 am

      It depends on the unit….if it’ worth fixing. Also a lot of times parts are no longer available. I had a 30 year old forced hot air furnace fail. It was in pretty good shape BUT for the heat exchanger WHICH was no longer available from the manufacturer.

  • Jon Hale November 23, 2015, 5:27 pm

    You might mention in your article that plenty of old homes have heater ducts that are insulated with asbestos that needs to be very carefully handled/disposed of.

  • Chris November 23, 2015, 5:49 pm

    I’d be interested in your thoughts about ductless mini-split heat pumps. I believe a small system with a couple of indoor units can heat a well-insulted house, especially in mild climate like coastal California. I’m not sure if it’s a DIY project or not given the need to inject the refrigerant but other than that it seems like it would be easy enough.

    • Mr. Money Mustache November 23, 2015, 6:14 pm

      Those things are a great invention, thanks for bringing it up Chris. I actually helped to install one on a new house I was building and the part with the refrigerant was surprisingly simple. You basically need a YouTube video (or an A/C technician friend) and a little pump like this: http://www.harborfreight.com/25-cfm-vacuum-pump-61245.html

      • afox November 23, 2015, 8:55 pm

        Yes, very surprised someone would install anything BUT a mini split in a home that does not already have duct work. The new heat pumps are very efficient down to temps around 1-5 Fahrenheit. Using one of the many calculators on the web based on electricity and natural gas rates in Colorado and the heat pumps are very close to to a natural gas furnace in cost per BTU. Add in the minimal installation costs and the savings in not having to install duct work and heat pump seems like a no brainer. No duct work also frees up valuable (and expensive) interior space. If possible to go without natural gas there are real savings in not having to pay service charges (the first $1-$15 of typical utility bill is service charges).

      • Daniel November 24, 2015, 9:35 am

        I have installed several of the ductless units with a friend of mine who is an HVAC guy (some side work for me). The condensing units are typically primed with the refrigerant already, so all that needs to be done is make create a vacuum in the lines you run (like MM said) and open the condenser lines and it fills itself. Very easy to install. My friend makes a killing putting them in. Ironically in MA you don’t need any licensing for HVAC work unless your working on units 10k lbs or more (however you do ‘technically’ need a licensed plumber to do any gas line running (unrelated to ductless splits).

      • AmicableSkeptic November 24, 2015, 11:59 am

        I’d love to see this article updated to show the installation of a heat pump instead of a gas heater. I thought my 96% efficient gas heater was top of the line until I learned that electric heat pumps can be over 200% efficient (put in 1 watt of electricity and they pull more than 2 watts of heat energy from the air). If you put some pipes in the ground and do a ground source heat pump you can get above 400% efficient, which is incredible. The big problem with ground source is people charge an arm and a leg for installation (10K seems like the low end). I would love to see a blog post where you self install a GS heat pump system (bonus points if you dig the trenches for the pipes with your own muscles instead of a machine).

        The only reason that gas furnaces can compete with heat pumps in terms of annual cost is the current extremely low price of gas compared to electricity (it’s around 30x cheaper per BTU where I live). This is what has kept me from replacing my current gas furnace. But, thinking about our planet’s future a heat pump system powered by a solar array would have a much lower total greenhouse gas emission than a gas setup. As rich retirees we should probably be the early adopters of this new tech.

      • Brian November 24, 2015, 7:17 pm

        Heads up, you will need to get licensed by the EPA before you can work on AC systems. The EPA actually makes it illegal to work on refrigeration systems without a license (called a CFC license), due to the damage that refrigerants can cause to the ozone and global warming if you don’t properly contain them. In fact you cannot purchase refrigerant from a supply house without showing your license. I’m going through this certification process now.

        • Joe Dangberg November 28, 2015, 9:33 pm

          The good news is it only takes an hour to study and $60 to take the EPA 608 cert exam for residential work, and the study material can be found for free online. This is a minor hurdle.

  • Laura November 23, 2015, 5:50 pm

    Great post! My furnace is probably original on my 1950’s house… It still works though, and in San Diego we don’t use it a whole lot during the year. In what way are old furnaces inefficient? Doesn’t combustion of the same amount of natural gase create the same amount of heat? Inefficiency seems to imply the heat is going somewhere other than to heat the house. If so, where does it go?

    • Mr. Money Mustache November 23, 2015, 6:10 pm

      Good question! In older furnaces, much more of the heat goes up the chimney. But in San Diego, you don’t need a furnace so you are wise not to spend money on it. Get an air-to-air heat pump if you ever need a source of heat in the future.

      • Laura November 23, 2015, 7:21 pm

        Thanks, I just learned about something new!

        • Tony November 25, 2015, 2:51 am

          Laura. The newer furnaces also use outside air for combustion. This is much more efficient than using household air.
          The reason for that is that when a furnace uses inside air for combustion it creates a vacuum (lower pressure inside the home then outside atmospheric } of sorts in the home and allows more outdoor (read cold) air to come in through the cracks in the homes doors and windows.

          If we could ever find a way to pressurize our homes efficiently to keep the cold air out we could heat them with candles

          • Julia November 25, 2015, 10:02 pm

            Look into Passiv Haus certification. Those houses can be heated with body heat, sometimes!

  • Charlie November 23, 2015, 6:52 pm

    I was just thinking about this subject but I am also in the heat pump camp, since I live in a one bedroom condo in a midrise building.

    The heat pump has been working poorly for years now, and also has a slow refrigerant leak, and I’ve been kicking the can by having a technician come replace the refrigerant every spring when the weather starts turning hot. I’ve wanted for the longest time to replace the thing with some nice new and presumably much more efficient model, but every time the urge strikes I find that I don’t know how to shop for one. I don’t know whether any given model would work in my particular condo, and when I’ve asked technicians about replacement they tell me it will cost me about five thousand dollars. I don’t know if that’s a fair price of if I would be getting ripped off by doing that.

    Just not knowing the lay of the land here is the biggest obstacle to getting this done right.

    • kristen November 24, 2015, 11:34 am

      You might want to check out EnergyStar.gov’s buying tips and qualified products list: https://www.energystar.gov/products/heating_cooling/heat_pumps_air_source

      Refrigerant can be very expensive, and unfortunately it is also pretty bad for the environment too. Old refrigerants were ozone depleting substances and also greenhouse gasses thousands of times more potent than CO2. Newer refrigerants usually are no longer ozone-depleting, but they are still potent greenhouse gasses…and they are often very expensive. If you care about this kind of stuff, you might want to get a ask a technician to help you install your new one, because they are required to bring equipment to recapture/recycle the old refrigerant (unfortunately, not all contractors adhere to this requirement). If you don’t care about that kind of stuff just make sure you get your refrigerant charge just right and use the right refrigerant for your equipment! Under and/or overcharging your system or using the wrong refrigerant can lead to damage or inefficient operation, not very mustachian.

    • Lucas November 24, 2015, 5:49 pm

      Two brands that are basically at the top are Mitsubishi and Fujitsu. Both make units that heat in as low as -26c/-15f ambient temperature outside. Perfect up here in Atlantic Canada.

  • Tom Bri November 23, 2015, 7:15 pm

    Alpine is just a 30 minute drive from my house.

  • David TK November 23, 2015, 7:36 pm

    Is this article oriented toward furnaces in ventilation-based heating systems only? There’s no mention of radiators. My house has a clunky oil furnace with a steam delivery system and big old fashioned steam radiators in the living spaces. I’ve asked a couple plumbers and an energy assessor about replacing with gas, and they’ve told me that while gas is more efficient for air- and hot-water- delivered heat systems, oil is more efficient for steam-delivered systems. Bearing in sad, sad mind that switching to radiant heat isn’t an option (we’re 2nd floor in a 2 family home), it’s not clear to me whether the best environmental choice is to stick with what I have (to avoid disposing of a big chunk of functioning machinery that took energy to build), or if I should switch to a gas furnace even though it’s steam heat (because producing and burning gas is cleaner than oil on balance?).

    • Mr. Money Mustache November 23, 2015, 8:18 pm

      I wonder if you could replace the radiators with normal modern hot water units, then use a standard tankless gas water heater and a circulator pump, much like I did in my hydronic system. I’m not sure if you could keep the same old circulation pipes though.

      Oil is typically so much more expensive than natural gas that it’s good to get off of it whenever possible.

      Baseboard heater example: http://www.supplyhouse.com/Base-Line-2000-Baseboard-Heaters-796000

      • Eric December 1, 2015, 10:28 am

        If David’s steam system is a two pipe system, with a separate supply and return line then it might be possible. If there is a single pipe (combined steam supply/condensed water return) into each radiator then it is not possible to convert.

        Even then, converting from a steam to hot water system can be tricky. HeatingHelp.com is a good forum with lots of steam heat experts exchanging info.

  • Rebecca Stapler November 23, 2015, 7:54 pm

    Nicely done! We recently replaced our boiler, so I know how much work that must have been. It took about 2 days for our installation. We got a rebate because our boiler was 40 years old, and we wouldn’t qualify for the rebate if a licensed contractor didn’t perform the work. I still don’t have the DIY confidence to attempt this on my own, but I’m sure that there are many who do, and $1,000 for a new furnace is a great deal — no rebate necessary!

  • Freedom 40 Guy November 23, 2015, 8:11 pm

    Love the message of pushing your comfort zone. Something I try to do as a landlord, but I admit I need o do a better job of trying to do more myself. I guess I’d worry smith something like an HVAC unit I might do something wrong and burn the place down!

  • Jim November 23, 2015, 8:21 pm

    I replaced my electric dryer with a gas unit a few months ago and agree that for all the intimidation, gas work is much less complicated than they would have us believe. In my research for that task, I came across a Gas Test Gauge, which allowed me to pressurize my gas system to 15 psi with air (as opposed to the <1 psi gas pressure). By pressurizing the system before beginning any work, I was able to first locate a leak caused by previous work done by a professional, licensed plumber. After fixing his joints and adding my own line to the dryer, I was able to confirm that my system can hold pressure for over an hour! I am much more confident that my house won't explode thanks to this inexpensive tool. I highly recommend it to anybody who works on their gas system. Here's a link to the gauge:


    To use the gauge, you have to temporarily disconnect your gas meter, in order to pressurize the system downstream of the meter (the part in your house). With a short pipe nipple, the meter threads right into the inlet of your home's system, and thanks to the Schrader valve you can even use a bike pump to pressurize. I was able to find a video on youtube that demonstrated this step.

    I should also note that it's important to secure the air pressure from your appliances (with the ball valves in your gas piping located at each appliance). While this omits the last stretch of the gas system from the pressure test, it prevents damage to your appliances.

    Thanks for the informative post, MMM! Even after my successful dryer installation, I was wary of ever attempting to replace my aged, highly inefficient furnace. But now, it's on my list for next spring!

    • AmicableSkeptic November 24, 2015, 12:11 pm

      I replaced my old gas dryer with a new one a few months ago too. Originally I was going to pay Lowes to do the delivery/install because they price that so low, but then I found an awesomely priced clearance model at the Home Depot. The only catch was that they didn’t offer installation of the clearance model. I hemmed and hawed for days worrying about blowing my house up before finally getting it. I was blown away by how simple the install was. Since I was just replacing an existing gas dryer I simply used he gas shut off valve that was already installed near my old dryer and replaced it. The job boiled down to unscrewing a single gas pipe, 2 screws in the exhaust vent and unplugging he unit. After it was done I wondered at how I could have been afraid of such a simple task in the first place and I got $5 for the old dryer at the scrap metal yard to boot. To anyone who’s afraid of replacing their own gas appliances I’d say stop worrying and just DO IT!

    • David B December 27, 2015, 8:14 am

      Well shit that would be easy. I could just hook up my kegging system to the gas lines and pressurize it with that and I already have the gauges and the way to pressurize with CO2. Thanks for the idea the next time I work on that system.

  • Dave November 23, 2015, 8:28 pm

    Most sites say don’t do this yourself. Some warn you need many specialized hand tools to connect it to the central air unit

  • Norm November 23, 2015, 8:31 pm

    I have thought about replacing hot water heaters by myself. You can even buy those on Amazon. But I wouldn’t know where to start to buy a boiler.

    I wish I had the time to do all of this. But on a related note, I got a $200 lesson in my own stupidity this weekend. Our rental property’s heat stopped working Saturday night. I’ve re-lit a pilot before, so I tried it and wasn’t getting anything. Couldn’t figure it out. I ended up having to call a 24/7 contractor who came Sunday morning. Turned out the pilot was a dummy switch because it was turned into an electrical ignition, and there was an Emergency Gas switch I never noticed before (had only registered to me as “red switch – don’t touch”). We had shown the apartment Friday night and the guy must’ve flicked it off! It is right next to the basement light switches. Still, it ended up being $200 to turn on a switch! If it was my own house, I could’ve spent a few cold days eventually figured it out, but since we had tenants and the temperature is below freezing at night now, I couldn’t afford to spend the time on it.

    • ScubaNewbie December 4, 2015, 9:15 am

      And now you know and you’ll never have to repay that lesson again! Husband and I aren’t great DIY’ers yet but one thing I insist on is when we do call the repair guy, go down there and stand next to him while he does his work. We had HVAC guy come once and all he needed was to clear the drain line (HVAC kept shutting itself off, apparently because water was backed up clear to the unit). When it happened a few years later guess who DIDN’T have to call a guy. We cleaned it out and recently redid the line so it didn’t have an opportunity to kink and create the blockage at all. So yeah, if you were truly MMM you’d have paid the $200 over and over again because you wouldn’t have learned anything.

  • Peter November 23, 2015, 9:06 pm

    I had always assumed that in Canada more specifically Toronto, Ontario area where I am that you had to have a license to do work on Gas appliances. Perhaps I wrongly assumed that the city would not even issue the permit to a non licensed home owner. And I might agree that is a good practice. Not to say I could not figure it out and obviously you did as well, but I am not sure I would want to buy a house from someone who did their own DIY gas furnace install. And yes electrical is the same thing. And I don’t think you could rely on the inspectors to keep the amateurs in check.

    Sure there will be some smart, conscientious detail oriented people who will try and do it right. But the vast majority of DIY home owners will not have that quality. Looking at the DIY wiring and home renos I have come across makes that obvious. Would you disagree? The only flaw in my statement is you can get contractors who are just as bad and inspectors who miss that too. But enabling the home owners is not a fix to that problem.

    • Bill December 1, 2015, 10:02 am

      I guess the homeowner DIY’s that we notice are the terrible ones. Competent DIY’ers do a job indistinguishable from the pros. It’s important to know your own limitations. In my current house, there is a switch in the guest room which turns on the ceiling fan. The switch next to it turns on the light, at which point the ceiling fan goes off. I haven’t had tome to resolve the problem yet, but I did disconnect the ceiling fan completely, because that was the switch which ran the hot neutral (!) to the bare ground wire for return (!?!?!).

      In a previous house, the guy ran out of wire, so he substituted green for everything at the service end. It made it difficult to install GFI’s to get up to code, to say the least. At the other end, I hired an electrician to replace the notoriously flammable Federal Pacific panel with a new one, and he saw white wires coming into the box and assumed 220v. The sawzall was not happy with that.

      In both cases, homeowners who obviously know even less than me about electric tried their hand at it. It’s kind of frightening. Know your limits, do more research than you think is necessary, and go to town, or hire out what you don’t know.

  • Danny November 23, 2015, 9:12 pm

    I had a similar experience this past summer when my air conditioner stopped blowing cool air. It was low on refrigerant, and I wanted to attempt the repair myself. I was really surprised how difficult it was to find clear instructions for adding refrigerant, and of course every forum post where someone asks for information is followed up with replies cautioning that this should never be attempted by an “amateur”.

    Turns out, it’s a relatively simple process. I was able to purchase a lifetime supply of R-410A and all of the gauges/tools to add it to my unit for less than the cost of having a professional out just once!

    • David B December 27, 2015, 8:28 am

      Hey Danny! Could you give more details on purchasing R-410A? I need to do some work on my AC system (moving the whole furnace to a different part of the attic)

  • longwaytogo November 23, 2015, 9:24 pm

    Nice job! My father and I replaced the nearly defunct inefficient 1940ish oil furnace in my great grandmothers old house so me and my buddies could live in it for a few years post college/pre marriage. ($500 a month split 4 ways! Wish I had those housing costs again :)

    It took the two of us less than 8 hours and carrying the new one in was the hardest part!

  • Jim Grey November 23, 2015, 10:15 pm

    I get it: going fully Mustachian, this makes full sense.

    Yet I’m not there yet. And when I decided that the 42 (yes, 42) year old electric furnace in my house was nothing but a ticking time bomb, I paid a heating and cooling company to install a new Rheem heat pump and air handler.

    That thing ended up being faulty in a whole bunch of ways — ways beyond my ability to cope with. The installing company replaced the air handler twice at no cost to me.

    I am moving toward full Mustachianism. But while I get there, I am so glad I paid this HVAC company to handle this. It has lowered my stress considerably.

  • Ben E. November 23, 2015, 10:16 pm

    Thank you for posting this. I never would have considered doing a project like myself. Now I will! One question: I noticed that the heater you chose is described as very efficient but it isn’t Energy Star-rated. I share your views on energy efficiency, and to make purchases simple, I generally insist on an Energy Star rating. Am I missing something? Could you share your thoughts on this? Thanks again.

    • AmicableSkeptic November 24, 2015, 1:24 pm

      The Goodman gmvm960805cx is energy star rated, but costs $600 more at Alpine. As far as I can tell the only difference between that unit and the one he installed is that it is a two stage unit. A one stage unit can only turn on at full blast while a two stage unit can do either full blast of some lower mode (like 65% of full blast). The two stage unit will run it’s high stage to warm the house up when your heater kicks on in the morning (because you’re a good mustachian who turns down the heat over night) and then use it’s low stage to maintain that temperature. A two stage unit isn’t inherently more efficient in terms of gas consumed but it will probably keep you more comfortable by providing a more constant low heat during the day instead of bursts of high heat followed by periods of cold. Two stage units also generally have more advanced electric blower motors that can be 40% more efficient than the blowers used in older designs. This means they will likely use less electricity and save you some money that way, but probably not enough to pay for their extra cost. You can read a more detailed scientific comparison here http://aceee.org/files/proceedings/2006/data/papers/SS06_Panel1_Paper16.pdf

      Before you read that though, if you’re thinking about efficiency no gas heater can EVER beat a good heat pump. This is because a heat pump pulls heat out of the air so it can be more than 100% efficient. A 96% efficient gas furnace loses 4% of the heat created by burning the gas to exhause outside your home. A heat pump sucks over 2 watts of heat out of the surrounding air for every 1 watt of energy you put into it and thus can have an efficiency of over 100%. Your total efficiency for a heat pump depends on how efficiently your electricity is generated and transmitted to you, but with solar prices dropping it is now economically feasible to cut out most of your draw from the utility by installing solar panels on your roof.

      Financially the extremely low price of natural gas means gas furnaces are still the cheapest to operate, so if you’re limited financially it would probably make sense to install a gas furnace and then spend the money you saved on improved installation. But, if you’ve reached FI and want to be as efficient as possible a ground source heat pump powered by solar is probably your most efficient option. Here’s some more in depth analysis on the efficiency of heat pumps http://aceee.org/files/proceedings/2006/data/papers/SS06_Panel1_Paper16.pdf

  • FormerFrontRangeGuy November 23, 2015, 11:06 pm

    For some folks it may be worth it to go to a fully modulating furnace, with a variable output burner, variable speed blower, etc. From your supplier, a modulating version of your example unit is about 50% more costly and is available from them in only in a 97% efficiency version. Other manufacturers make fully modulating versions in efficiency ratings down into the medium (80-something percent) range.

    One reason to choose the fully modulating unit is that it usually runs at a very low level and is very quiet. That can be a big deal in some houses where the furnace is somewhere in the main living space. At full speed, the main blower and draft induction fans can be rather loud, and sometimes cause duct noise. Our modulating furnace, in contrast, is almost never audible, though it is in a closet in normal living space.

    One reason to choose a unit that is medium and not high efficiency is that you can use the existing flue arrangement. High efficiency furnaces are usually vented with plastic or stainless, horizontally to the outside, and this may be difficult in some houses, requiring the creation of chases or soffits, and drywall surgery and paint.

    Lastly, some municipalities prohibit DIYers from doing their own natural gas work of any kind, even when they allow them to do other plumbing. I don’t like that, but IIRC it’s the situation where I live. Otherwise, I think this is a good DIY project for anyone who is willing to learn and do careful work.

  • Maverick November 24, 2015, 2:24 am

    I completed a three A/C unit installation myself consisting of a 3-ton, 2-ton, and mini-split. I had an online source who performed the load calculations and size ducts for me using proprietary software. The more difficult part I found was doing all the custom sheetmetal design for transitions and finding a local fabrication shop to work with me. I used Sketch-up. The fab shop also helped me by recommending duct sealant that eliminates the use of silver foil tape (which professionals would not use). The only part I had to sub-contract out was the installation of refrigerant lines as I do not have the specialized brazing, nitrogen purge gas, charging tools, or refrigerant purchase license.

    • David B December 27, 2015, 8:36 am

      I wish i could find a professional to do a the refrigerant parts of an install. I hired a guy this summer to do AC work but it quit after a week and he won’t come back out to work on it again after taking my $700 to simply hook up (no running, just braze this to this) then charge lines to the condenser. Any suggestions on finding a good person/company to do this? He is the first guy I’ve hired to do anything around my house as I normally DIY everything, but at this point I’m looking up how to get EPA certified so I can just finish the install myself

  • Mr I. Accountant November 24, 2015, 3:57 am

    Great to see that you found the DIY project to be far easier than most people would have expected – if only people would try these things (or at least research them) before pulling out their wallets they could save themselves a lot of cash!

    I love your attitude of self-sufficiency and personally get a lot of satisfaction from attending to these sorts of things myself. I replaced the bathroom heater light myself the other week as an example, and plan to install the heating system in my renovation/extension myself also. And I’m an accountant that sits in an office all day!

  • Josh November 24, 2015, 4:34 am

    Seeing articles like this and comments like Maverick’s are reassuring – turns out there is still a contingent of meat eating people out there willing to combine thought and effort to improve their lives. Ayn Rand would be proud, if she wasn’t too pissed off about Amtrak.

    • AmicableSkeptic November 24, 2015, 12:17 pm

      Some of us DIYers don’t even eat meat!

  • Dean November 24, 2015, 5:31 am

    I believe here in Australia (at least where I am) it’s illegal for much of that stuff (gas, water, sewer, electricity, etc) to be installed DIY, it has to be done by a licenced plumber/electrician/etc.

    Still, nice effort on getting it installed. I’m sure so many other people use crappy old inefficient appliances without even knowing how inefficient they are. Fridges are a major culprit.

    • longwaytogo November 24, 2015, 6:01 pm

      I find that hard to believe, though I’m in US. It’s illegal to do most of what you mention on someone elses home without a license. But you can do whatever you want on your OWN home. You still have to follow codes and get it inspected but you can do it.

      • Kip November 25, 2015, 6:33 am

        I’m in Australia as well and yes it is illegal to do those things DIY, even if it is your own home. The penalty is up to AUD$40,000 for individuals and even more if someone is hurt.

        Australia seems to thrive on making many things illegal, such as riding a bicycle without a helmet.

    • Bill December 1, 2015, 10:20 am

      Not sure about install, but our Texas town requires a septic inspection three times a year. This costs $250 per year, and takes literally about 5 minutes. Alternately, there is a class you can take for about $200 one time, that certifies you to do it yourself. Of course, then you have to put your head in the shitter three times a year, so for me this one is worth it. I stick to indoor plumbing jobs, even though those are gross too sometimes. I think for most of the things you are talking about, you get a permit and you can do the work, or a contractor registered with the city can do the work.

  • Jim Wang November 24, 2015, 6:21 am

    There’s value in understanding a system and doing it yourself, I don’t know if I’d replace my own furnace but understanding what the various parts are, where to get replacements, etc. can be extremely valuable when it comes time to fix something. Not only do you save money, but you save time too, it sucks to learn you have to wait two days before someone can come out to diagnose a problem.

  • Karen November 24, 2015, 6:40 am

    I had my furnace and A/C replaced a couple years ago. Doing it myself is beyond my basic (yet improving) DIY abilities. I think knowing your own skills is important before taking on something like this.

    Nonetheless, I was able to still replace it and save several thousands of dollars because I replaced them during the time when the Ontario Government was giving money back for eco renovations. Essentially it worked out that the government reimbursed me for half of the overall costs of the units and installation and I now have a high efficiency HVAC system and the low bills that go with it.

  • The Lazy Electrician November 24, 2015, 7:14 am

    You forgot one important step: bonding the CSST to the ground in your panel. CSST is notorious for developing pinhole leaks due to lightning strikes, so take a piece of #6 copper and run it from your panel to a pipe clamp on the black metal pipe at the point where the CSST begins..

    • Mr. Money Mustache November 24, 2015, 7:59 am

      Excellent – thanks for the advice Lazy E.

      I am confused though: I thought gas meters already had to be grounded (and both arms connected together electrically as well) – wouldn’t a grounding of the black pipe at the switchover point just be repeating the same ground connection?

      • Florida Mike November 25, 2015, 8:02 pm


        Do some quick research on CSST and the specialized bonding\grounding for it. As Lazy said, CSST has some weakness with regards to lightning hence the need for additional bonding\groudning points.

        • Bill December 1, 2015, 10:39 am

          Another issue with CSST in my area is roofers. They are notorious for putting nails through that stuff and having the house catch on fire. There was a lot of it used in the next town over, and their fire department is huge.

  • kaz November 24, 2015, 7:29 am

    have you checked with your insurance company that they will cover your work? In case you find that they wont pay out if something goes wrong with it and it blows up the house or makes someone sick because it wasnt installed by a licenced plumber/gasfitter.

    • Mr. Money Mustache November 24, 2015, 8:04 am

      Another good question. If you have your work permitted and inspected, the insurance company usually does not care who does the work (from my experience so far).

      But another thing to consider: if you ever buy a used house, especially one that is many decades old as they are in my neighborhood, you are inevitably getting LOADS of haphazard, unpermitted work from past owners along with the deal. Plus, construction standards were very low in the olden days to begin with, so even a completely stock house will have problems far greater than this well-done DIY gas furnace.

      Insurance companies know this and they still cover older houses, because it’s still not all that risky. You do get a discount for a newer house however.

      A single family house is just a simple shelter for humans – a glorified cave. Not all that expensive and not very complicated, so nothing to be afraid of.

      • FromerFrontRangeGuy November 24, 2015, 9:22 am

        Years ago an insurance industry representative on the Hometime radio show (hosted by Dean Johnson) addressed this in connection to a question on electrical work. I guess gas work would be the same.

        If memory serves, their position was that they would cover damage related to work done by homeowners if it was done under a permit, whether it met code or not. If there was damage related to DIY work that was unpermitted but still met codes, that would also be covered. The danger was DIY work that was unpermitted and where a code violation was related to the damage. They could refuse to cover that.

        As far as municipal requirements for a licensed person to do the gas work, it may be part of the legal position that the main purpose of permits and inspections is to protect the public in general and not the homeowner specifically. Bad DIY plumbing may be seen as mostly a hazard to the homeowner, while bad gas work can endanger others/neighbors/tenants. A supreme court case in our state a few years ago dealt with this issue, but that’s only one state.

        Your comment about all the haphazard, unpermitted work already out there is spot on. For grins I used to browse around the “owner boners” thread at misc.consumers.house. Hilarious stuff!

      • kaz November 24, 2015, 3:29 pm

        I was looking at a house to buy and noticed that they had installed a shower without obtaining a permit (advice to home buyers, always check the contents of the house against its original plans and that any additions have the appropriate council consents). When I asked my insurance broker if they would cover the work they said no – so any damage done by a leaking shower would be my problem. So please, make sure you get all necessary permits, otherwise you leave a very expensvie problem for someone down the line.
        The problem with gas fittings is that if they blow up the house it will be nigh on impossible to prove that it was installed according to code (if unpermitted) or that you had not made a mistake in adjusting it post install. NZ has a decade’s worth of properties that were built according to code and signed off by Council, but turned out to be leaky (due to the treatment of the timber framing) – and there is no insurance coverage for any of it. Insurance companies usually use any excuse to not pay out. Bearing in mind the extent of damage to other properties and people caused by house explosions it could result in the loss of your entire cash stash in one lawsuit, turning you into a very poor unemployed person overnight. So I recommend that you get written consent from your insurance company prior to doing any gas or electrical work so they don’t have grounds to deny a payout.

  • Billy November 24, 2015, 8:28 am

    Re: DIY furnace repair, if you’re hesitant about jumping in, you can always get a licensed pro to diagnose the problem, which can be anywhere from free to less than $100 for the trip charge. Get them to tell you exactly what the problem is and how they would fix it. Most HVAC techs I’ve met are willing to answer questions like this.

    I did that when my gas furnace blower motor went out, and once the problem was pinpointed, I just got a replacement blower on eBay, found a YouTube video on how to switch it out, and saved $500 over what the pro had quoted me to do the job. Like MMM says, once you open these things up, they’re not that complicated or scary.

    • Val November 25, 2015, 9:00 am

      And most furnaces have an error code system that should be pretty obvious (a series of blinks indicates error 17 – insufficient airflow for induced draft blower, e.g.) Look up error codes for your brand online, and figure out how to read them. Then you might even save the $100 trip charge. For mine, there was a dead bird in the outflow PVC flue, and the motor was stuck. Remove some piping and out he fell… I don’t know if someone professional would have ordered a new motor before checking for instructions, but I did because I’m cheap…

  • Bob November 24, 2015, 8:30 am

    After the Radiant head experiment I was inspired and took upon myself to replace the boiler for my house. I had amazing experience with Alpine Home Air. They have technicians that will help you and they really know their stuff.

    Even if you don’t want to do the work yourself, buying the equipment yourself will save you from the contractor markup. Here in DC contractors mark up the cost of the equipment up to 200% above the wholesale price you can find online.

  • frank November 24, 2015, 8:53 am

    When we added on to our old house ( and drove every nail ourselves in true MM style) we added gas to the house and installed a new 94% AFUE furnace.

    Like you when I hear the words “qualified installer” it pisses me off too. I work on the principle that as I have a PE license (retired this year) and have worked in mechanical infrastructure (building wafer fabs) for 30 years, I am more qualified than just about anyone!

    But like you I got the same old crap about how “complicated” it is.. Geez, String theory and Quantum physics is complicated, not installing a furnace!

    • Zac November 24, 2015, 1:32 pm

      I understand string theory and quantum physics much better than plumbing and HVAC/R thanks to the wonderful University of Michigan… but I’m learning quickly how to do these more practical things for myself. It truly seems like nothing is beyond comprehension and eventual competence if you make it your goal to learn and do.

      Thanks for another great post, MMM!


  • BMG November 24, 2015, 9:10 am

    I’m a carpenter, but love to learn new skills and use them where I can. I was afraid to tackle HVAC until I found out that a buddy’s dad had taught HVAC at the local vocational school. We installed all the duct work and two new furnaces, air handlers and condensing units for the A/CC in our 100 year old gutted house.

    The process was straightforward and very enjoyable. The only thing that may have been tricky was connecting the copper line set to the condensing unit and the freon side of setting up the A/C.

    I have propane and did all the piping, checking for leaks with soapy water. All the intake and exhaust was PVC. Just like plumbing a DWV system.

    One may be able to find a retired HVAC guy or teacher in the area by posting on craigslist or asking at supply houses. In all the trades I’ve learned there is always someone who has the knowledge to share but isn’t in business anymore. Just make sure they are comfortable with newish technology. A few 20 dollar bills or some beer is usually more than enough to solicit some expert help.

  • MJB November 24, 2015, 11:32 am

    With winter upon us, the frugal masses might appreciate tips on avoiding service calls ($$$) for mechanicals. With furnaces, there’s lots of DIY fixes (flame detector cleaning, resetting limit switches, for example) that are safe to attempt with obvious precautions (turn off power to system for starters). Lots of good YouTube videos for learning this stuff. Same with hot water heaters. You can fairly easily replace a thermocouple (common failure point) for 12 bucks, in about a half hour, with a screw driver and a pair of pliers. Love these DIY posts!

  • yyz guy November 24, 2015, 11:54 am

    I would just add…”winter is coming”. I wouldn’t dream of starting a first time DYI furnace project days before the temperature is going to drop below freezing. Please wait until you don’t NEED the thing during the time it will take to do the job (and double your estimated time and number of trips to the supply store). I’d wait until spring or summer before starting, but that’s just me. When the impending temperature drop arrives (american holiday weekend too), there won’t be anyone to bail you out if things don’t quite work out.

    I would really like to try this project myself too. My concern is my furnace located in the attic in very tight quarters and awful working conditions. I’d be a lot more inclined to try it if it were located in an easy to access location.

  • Steve November 24, 2015, 12:40 pm

    How do you go about evaluating if this is a ‘net positive’ for the environment? Obviously, throwing out an old furnace and associated materials has to go somewhere. And there is buying and shipping in a new furnace. This isn’t being done on the scale of a new housing development… And the reduction in gas consumption due to efficiency, as you point out in the article, takes years to make financial sense, so how do we know if it makes ‘environmental sense’?

    • Stephane November 24, 2015, 3:02 pm

      My biggest problem is I suspect gas will go the way of the dodo soon, so getting a high efficiency furnace might not make any sense. Add to that they are very expensive, and you could add a decent amount of solar heating for the price.

      • Chris I November 25, 2015, 10:24 am

        What makes you say that? I’ve read that we will have a glut of natural gas for decades because of fracking, and I don’t think there will be political will at the federal level to properly price carbon emissions at any point in the near future…

    • Eliza November 24, 2015, 8:02 pm

      You would need to look at the lifecycle analysis for furnaces to figure out if the embodied energy (the materials, manufacturing, delivery etc) outweighs the energy savings. Generally, because appliances use energy during their lifecycle, the environmental impact during the use phase is more significant than the embodied energy. For example, there’s a rule of thumb that replacing a fridge that is more than 10 years old is good for the environment because the efficiency of new appliances outweighs the embodied energy. That said, while energy efficiency gains might make environmental sense, it doesn’t always make make economic sense as it depends a lot on the cost of energy.

    • Luke December 5, 2015, 8:33 am

      An old furnace is completely recyclable. You may even get $30 for it by taking it to the scrap yard.

  • Bob Derek November 24, 2015, 12:49 pm


    Where I live almost everyone has forced air cooling but baseboard heating so this does not help us that much. And, if it involves gas, thanks but I will leave that to a professional. I don’t mind paying for good work, and you must not live in a place where houses blow up because someone decided to add any kind of gas appliance on their own.

    Think BOOM! So in your lexicon “NO BOOM” is worth a lot.

    • David B December 27, 2015, 9:19 am

      I just wish I could find a contractor that would do a better job than me, so far I’ve struck out finding people who do a decent job at… their job. I guess I’m a bit of a perfectionist when it comes to plumbing/electrical/HVAC and I’ve read the building codes for all of it.

  • Steve M November 24, 2015, 1:23 pm

    Hi MMM, Great post, I replaced my furnace myself several years ago. One thing I spent a fair amount of time calculating was the size of the replacement furnace. I replaced a 30 year old unit which I figured was around 54% efficient. As far as I remember, the BTU rating was the gas consumption on the input (as labelled on my old furnace)… Either way, this is the time to assess the sizing of the unit. If you oversize the furnace expecting that bigger = better, you’ll end up with less efficiency and a shorter lifespan for the unit due to the rapid cycling. If you’ve increased the efficiency of your home in other ways (upgraded windows, insulation, etc) you may actually need less furnace than you had. There are many calculators online to help with the sizing, and the folks at Alpine Air are quite helpful.

  • JD November 24, 2015, 1:25 pm

    Thanks for the write-up. One aspect I question, though, is your recommendation to use the same size unit as the existing furnace. This advice is problematic as most older units are over-sized already, especially if you have made improvements to the building envelope such as insulation or air sealing.

    While the effects are not as bad as over-sizing A/C equipment, over-sizing a single-stage unit like yours results in short-cycling. Short-cycling causes needless wear and tear and prevents the furnace from reaching its rated efficiency. Anyone installing new HVAC equipment should do a proper load calculation (such as ACCA Manual J), not use rules of thumb or base on existing equipment.

  • shadowmoss November 24, 2015, 1:26 pm

    Sigh. Mom needs a new fan in her gas furnace in her mobile home. She found the make and model for me. She will hire a handy man(woman) to install it, but I may have to get off my butt and do it myself just to prove (to myself) that I can still fix things. Being a 61 yo female with a bad back shouldn’t keep me from doing this much. It is just the fan/blower assembly.

    After I do that I should be more ready to coat the roof of my own mobile. I come from a long line of DIY folks. Mom (84yo) was asking for a ladder to check her roof and was going to coat her own, but I put my foot down and said no.

  • Scoop November 24, 2015, 2:11 pm

    I did this about 10 years ago in Ontario. Some things I learned is yes this is a really, really closed industry but I was able to get both a very high efficiency condensing furnace and AC unit from what was USA Manufacturing and is now Surplus City Liquidators. You have to keep checking over and over for stock on something that works well in terms of size and efficiency (it’s all surplus/overstock), in my case a furnace, A coil, condenser and condensate pump. The whole thing was really well priced and I had it shipped to warehouse in the US and I picked it up and brought it to Ontario, note: the furnace must have Canadian approval stickers for gas connection here or nobody will touch it, my Amana did. Customs guys asked all kinds of commercial goods questions both ways but no big deal, it’s unexpected as not many people do this stuff as a DIY. Note that refrigerant is controlled and can have excise tax imposed. I drew up plans for all the transition ducts and had them fabricated locally, not very expensive, also had neoprene gaskets built into the transitions to limit noise transmission. Some stuff like the exhaust for the furnace and hot water(replaced at the same time), fresh air intake and a nearby window created some placement challenges, there are a whole bunch of rules one must follow there. I found and paid a local gas guy some cash to hook up gas connections to the new furnace and hot water tank and properly tag them which is important here. He called and verified that no separate inspection was required, he as a licensed guy was allowed to do a replacement, on new installs the gas company sends a different contractor to inspect the other guys work, that will be region specific. I also got him to braze, purge and leak test the refrigerant loop for the AC. The pre-load of refrigerant in the condenser was very close to what was required. In all I paid about $200-$300 for that work and he also provided the gas flex connection materials. A few issues occurred over time, fan relay broke on the furnace logic board, ordered another board off of eBay and bypassed it to run the fan full time until the part arrived, condenser on the exhaust blower failed, just swapped the condenser and the condensate drain plugged and backed up some water into the fan housing. All of this stuff was easy to fix myself, yes I gave up any warranty but I saved thousands on installing all of this stuff and the high efficiency furnace really is quite efficient so the savings continue. I keep a few common spare parts around for emergencies, the old semi working logic board, a spare igniter, condenser and jets etc. If I were to do it again I would drop the size of the furnace a bit more, even though it’s probably at least 30-40K BTUs smaller than the original, the duct work in older houses like mine is a big bottleneck and the fan has to run at fairly high speed to keep the heat rise within spec. That’s an exceedingly difficult thing to fix in a two story house without rebuilding half the house. Generating less heat and running longer with lower fan speeds might in theory make things more efficient. Sizing the furnace is a tricky thing, there are some calculators out there, definitely don’t go by what was installed, stuff from the 50’s/60’/70’s is way oversized relative to modern stuff. In Canada also you will often need funky transitions from the A coil to furnace, more heating requirement than cooling e.g. a boxed coil could be much smaller than the furnace plenum. This whole thing really can be done yourself and you can self support it after install IF you plan properly and have a very good range of mechanical, plumbing and electrical skills. No I am not worried about CO poisoning or the house exploding, I have a gas detector and 10 interconnected dual smoke/CO alarms in all of the appropriate places, you still need that stuff even if a “pro” does the work, things break. BTW some gas alarms are very prone to false alarms, my current Universal one seems to be better than the others, so far anyway, look at some reviews before buying.

    • Stephane November 24, 2015, 3:00 pm

      My understanding is you need a license to touch the gas. And if the gas furnace doesn’t have some licenced installer’s name on it, you could be in trouble, particularly with insurance and others…

      • Scoop November 24, 2015, 5:50 pm

        That’s why I paid a gas tech to do the final connection to the existing piping and properly tag both the furnace and hot water tank. There was a ton of labour in this project, no previous AC, all new venting and transitions to very old duct work connected to a gas burner/oil conversion. I did 95% of the work and the gas guy did 5% but I paid him a reasonable amount for that part so it is legit. I really wanted the proper tag on there, besides the insurance claim issues, my insurance company comes in and does full appraisals/takes photos every few years and the gas company could inspect at some point and red tag/shut me down. This is more about protecting myself from bureaucracies that could cause me future pain than an issue of safety, I have no doubt that I could have made the connections safely myself. Bureaucracies scare me more than gas explosions, failed car brakes, electrocution or any number of other bad things that could in theory harm me by doing stuff… In the end the whole install is as safe as it would be if someone else expended all the effort and arguably it’s much cleaner than a number of “professional” installs I have seen because I have more vested in the end result and I had the time to do it right. I also don’t need to pay someone top dollar to haul refrigerant lines through a tight crawl space and deal with other annoying time consuming things like dismantling and removing the old furnace etc. There is a ton of FUD around this stuff and a very protective culture in this and a few other trades so it can be tricky to find someone to do the legitimate hookup, I did it by networking with other handy people that do this sort of thing. Trades people can be found to do these things on the side, most companies will want the whole job on something like this for $5K-$10K so I wouldn’t even go there. Also on the refrigerant line side you need too much specialized equipment to make it a practical DIY, just get everything in place and have a pro deal with the line connections as the final step.

  • Stephane November 24, 2015, 2:58 pm

    The problem is, at least in most Canadian provinces, it is illegal to mess with gas appliances without the proper certifications. So most people cannot do it, though you could certainly shop around for appliances, but generally installers will only install the brand they are familiar with, unless you are really friends with someone. Personally, I think it is another reason to kick the old fossil fuels to the curb. When it is so dangerous they don’t want you doing it on your own, it might be too dangerous for my house.

    • Call 911 November 24, 2015, 4:21 pm

      And in New Jersey/Oregon, it’s illegal to pump your own gas.
      “When it is so dangerous they don’t want you doing it on your own, it might be too dangerous for my (car)”
      I guess you drive a Leaf?

      There are any number of rules/laws/regulations that exist either for historical reasons, or because some people can’t chew gum and walk at the same time. Governments the world over have decided they must protect the idiots from themselves, and mustachians get caught up in their very broad nets.

  • KY November 24, 2015, 3:44 pm

    So, I moved into this house about a year ago and this article got me thinking, “Hey, how old is my furnace?” Looking inside, I think this furnace was manufactured 12/85. Could I really have a 30 year old furnace? BTW: Looking at it, I wouldn’t be surprised if it had been installed without a license/permit. It looks amateurish with a couple of obvious flaws.

    • longwaytogo November 24, 2015, 6:09 pm

      Yes, it’s defintley possible you have a 30 year old furnace. I’ve seen plenty older; my parents still have their original from when the house was built in 1980.

      Also just because it’s shoddy does not mean DIY, plenty of house built cheap/quick by “professionals”

  • Call 911 November 24, 2015, 4:09 pm

    I haven’t been a poster here in awhile, but I’m still a reader.

    Those last 3 sentences are the reason I’m still excited to be here.

    I bought a 2012 Triumph Daytona 675 that didn’t run. The owner didn’t know why either. I low balled him and he took it.

    I have never successfully taken an unknown failed engine powered machine and fixed it. But “This is possible, and plenty of people with fewer advantages than me have accomplished the same thing many times in the past”

    So I started simple. Spark plugs, fuel pump and injectors. I got it running. Very, very badly, with a horrendous ticking. So I dropped the engine and pulled the head. No obvious head gasket/head/valve problems. But one cylinder didn’t move right. I opened the block and found a spun (missing) bearing. Parts are on order currently.

    Before starting, I didn’t really know what a “spun bearing” was, what it meant or why it happened. Now, I know all of those things. It isn’t running (yet). But I WILL fix it!

    Because I “get to work, read the instructions, tinker, make mistakes, learn, and succeed. And continue to build on that success, forever.”

  • Bill November 24, 2015, 4:38 pm

    That’s the way my dad taught me, by example, when I was a kid. Just try stuff and figure it out. Do that enough and you build on it. It’s probably the reason I’m an engineer today. Recently I needed to run 220v from the box, and did the whole project myself, including installing the breaker. It was easy, and I learned a lot and had fun. I also did it to code, which has changed since the house was built, so it’s the only circuit in the house that is up to current code (staples on wire every 4 feet).

  • Steve November 24, 2015, 8:58 pm

    MMM- Great post- love these DIY posts about projects people are terrified to tackle themselves. When we moved in our house several yrs ago, the prior owner had a “professional” HVAC company put in a high efficiency boiler. Thing leaked 3 times before I finally figured out the HVAC company that installed it was clueless (yeah, I’m a slow learner and apparently my town doesn’t inspect these installs too well or was never called in). Bottom line is it was leaking because they used copper pipes for the acidic condensate (rather than plastic tubing) and an inappropriate condensate pump. Pretty simple fix – corrected the condensate pump, used plastic tubing and a neutralization kit. Neutralization kit or aggregate limestone is needed because the acidic condensate can corrode drain pipes and septic tanks.

  • Mike November 24, 2015, 9:00 pm

    It seems that provided a reasonable conceptual understanding, good research skills, and an attention to detail, there are very few tasks (across all disciplines white color or blue collar) that can’t be figured out in a matter of days or weeks. The only challenge is when a project requires 10s or 100s of different tasks, since you have to weigh the months or years to learn and complete versus the value of time.

  • PurduePete November 24, 2015, 9:42 pm

    Great article MMM, I actually replace my own furnace with a help of a friend who works in the HVAC industry. We order a Goodman furnace just like you guys did from Alpine for about $500, after the installation, Goodman requires you to have it inspected by a HVAC contractor to have the warranty in place which you can ask any friendly local HVAC technician to do for a small fee…per my friend. Of course he helped me and out and I end up paying him his small fee in a form of a lunch. The hardest part was getting the old furnace out of the attic which was a bit heavy.

  • tlars699 November 25, 2015, 6:25 am

    I have read through my city’s permit system rules, and from what I understand of it, the city has cited specifically for HVAC and Electrical that in order to *get* a permit, you have to have a Master Electrician/HVAC consultant sign for it. (Plumbing also has this catch for big work, but puttering around your house with no significant value upgrade is allowed.)But they specifically list that for gas work you absolutely need a Master/Qualified technician to handle it for you. What do?


Leave a Reply

To keep things non-promotional, please use a real name or nickname
(not Blogger @ My Blog Name)

The most useful comments are those written with the goal of learning from or helping out other readers – after reading the whole article and all the earlier comments. Complaints and insults generally won’t make the cut here, but by all means write them on your own blog!


welcome new readers

Take a look around. If you think you are hardcore enough to handle Maximum Mustache, feel free to start at the first article and read your way up to the present using the links at the bottom of each article.

For more casual sampling, have a look at this complete list of all posts since the beginning of time or download the mobile app. Go ahead and click on any titles that intrigue you, and I hope to see you around here more often.

Love, Mr. Money Mustache

latest tweets