Our DIY Heat Pump Install – Free Heating and Cooling for Life?

A work of art.

To most of the Internet, Mr. Money Mustache is known as the quirky early retirement financial guy, and this is a blog about Money.

But really, I’m not a finance guy – someone who devotes most of his time to optimizing money. I’m more of a general Life Engineer – someone who tries to optimize everything that is fun and interesting in life, and money is just one of those things.

Optimizing means getting the most good out of something – whether it is money, time, health or happiness, while minimizing waste. This is what allows us to make win/win decisions (for example things that make you richer and healthier and happier), rather than win/lose compromises (giving up something you actually like, just to save or earn more money)

One of these win/win things for me has always been optimizing my own houses and buildings to be more comfortable and stylish, while costing less to own and maintain and heat and cool. After all, out of all possible decisions, your choice of home may have the biggest effect on both your financial and emotional wellbeing. Get a reasonable house that is close to your friends and your work, and you’re off to a great start.

 So anyway, this past summer all my favorite factors of optimizing, learning, effort, saving shit-tons of money and reducing loads of waste and pollution came together in the form of a DIY Heat Pump Installation on our commercial building downtown, the home of MMM HQ Coworking.

Why Are Heat Pumps Super Exciting?

Heat pumps are a technology that has recently jumped into prime time and are about to change everything about houses, just as the iPhone did to the tech industry about twelve years ago and just like electric cars are doing to transportation right now. The reason is that they have these fundamental advantages:

  • Heat pumps do the double-duty of heating and cooling any building way better than our existing systems do, but with only one machine.
  • They are super easy to install, and way cheaper to run. They also allow houses and buildings to be constructed more cheaply (less materials and labor).
  • They eliminate a big part of the world’s pollution that is caused by burning oil or gas for heat (as long as you get your electricity from clean sources).
  • And yes, nowadays they work in virtually all climates (down to -20F / -29C): tech improvements have shattered the old limitation where they only worked in places without a real winter. 

How Does a Heat Pump Magically Suck Heat Out of Cold Air? 

Heat pumps save money and energy because they aren’t generating heat directly like an old electric baseboard heater. They are mostly just  moving heat around – from inside to outside in the summer, and from outside to inside in winter. 

To many people, that second situation sounds like magic, but that’s just because of our skewed perception as human beings – a creature that evolved in the warm tropics of the planet Earth. Really, there is plenty of heat even in winter air – if you view it through the Eyes of Physics:

Every spot on our life-nourishing Earth has loads of heat energy (Kelvins), which means it’s easy to harvest some of it.

So, a modern heat pump can easily suck loads of heat even out of air that feels cold to your skin. It does it like this:

Summer vs. Winter modes of a heat pump. The key to everything – fridges, A/Cs and heat pumps – is that the refrigerant gas gives off heat (gets hot) when you compress it, and absorbs heat (gets cold) when you expand it.

You know what else does this exact same trick? Your own FREEZER! Those things typically maintain an inside temperature of about -10F, which means that somehow it is sucking heat out of the air even at sub-zero temperatures, pumping it out to the coils underneath with a fan blowing past them. And if you put your hand there to feel that airflow, what do you feel? Warmth! 

Show Me The Money

Here’s our gas bill history – Yuck! Most significant is the fact that the monthly fee-for-nothing ALONE had risen to $40. $480 per year before you even get any heat out of it!

Before we get into the real details, check out the quick numbers for the heat pump I just installed. Note that I live in Colorado, which has lots of heat and a moderate amount of cold – right about what you’d expect from our position halfway between Maine and California.

  • Cost of the system including all install materials: About $4500
  • My building’s previous annual gas bill: $951
  • Our new annual electric bill for heating and cooling (estimated): $275
  • Annual savings: $676

Annual return on investment (ROI) rate: 15%


Even better: That $275 annual figure for our electricity consumption is what we would have paid, if we had to buy all our electricity off the grid at 10 cents per kWh. But since we generate a surplus of power from our DIY solar array, our net cost is much less than that.

You could even say that all of our heating and cooling is “free” on an ongoing basis, although we did spend $5000 to build the 5.5 kW solar setup in the first place.

So Is A Heat Pump Really a Do-It-Yourself Project?

Our installation team celebrates at the end of a successful project. To be fair, Mr. 1500 and I are both pretty experienced tradesmen, but this felt like a relatively easy project to us.

In a word: Yes, if you are a fairly competent do-it-yourselfer, and you choose a DIY-friendly heat pump kit. It is considerably easier than installing a gas furnace or a metal roof, but not as easy as putting together IKEA furniture. 

Our first install took about 16 person-hours of work for the main job (two people working a full day). Plus I spent about another sixteen dusty hours upgrading the duct work and building custom metal shapes to route the air because our coworking building was so old that the original asbestos-and-mouse-shit ducts were just not worth keeping.

Hmm.. Okay yeah I think I’ll go ahead and replace these ducts.

The value of doing it yourself is that furnace work is one of the biggest returns on your time as a homeowner. Where I live, even a gas furnace + air conditioner replacement can cost $10,000. And although a heat pump hardware only costs about the same amount as conventional furnace+AC ($4000), the companies like to charge more for the newer stuff (or even worse, try to convince you that you’re stupid for even asking about it!).

In other words, even conservatively speaking, for a basic installation you are saving about $6000 in exchange for doing that 16 hours of work, which amounts to a solid $375 per hour.

But Wait! Don’t forget about Rebates!

Even if you’re not a tinkerer, there are some good programs out there that will help subsidize the cost of an upgrade like this. The US EPA offers federal tax credits for lots of things including heat pumps, and local agencies have their own programs – for example neighboring Fort Collins will chip in $2200 towards a unit like ours, which could cover most of the cost of a professional installation.


So if you are ready to upgrade to a heat pump, you either need an honest HVAC company who will install a reasonably-priced machine for you and charge you a reasonable hourly rate. Or, you need to flex your Money Mustache Muscles on the project and do it yourself.

Of course, I chose the latter approach as always, so let’s get into the details of our install!

Step One: Pick a Heat Pump

There are two things you’re looking for here: physical size and heat output. 

The size and shape of indoor portion (the air handler) of the new system have to be similar to your old furnace, or you need to have a plan for how to adapt the new one to blow into your old pipes. As you’ll see below, I chose to do the adapting.

As for the heat output, old furnace was a “100,000 BTU” unit, which is a measure of the amount of natural gas it can suck in and burn each hour. Since it was only about 75% efficient, the heat output was about 75,000 BTU (the real units here are the archaic “British Thermal Units Per Hour”, but all you really need to know is that this is still more than enough to keep our leaky, sprawling 2400 square foot brick building warm easily through even the coldest winters.)

In the most extreme situation (for us this would be a 24-hour period where the temperature is barely above 0F, and it typically does happen at least once every few years), I measured that our old furnace was running for about 8 hours per day, which means our average heat loss was about 25,000 BTU on a continuous basis (75k multiplied by ⅓ of the total hours in a day)

On the cooling side, we had virtually no air conditioning. Just a few crappy portable units scattered throughout the building, with a total combined cooling power of about 20,000 BTU. This wasn’t quite enough to beat the heat in the event of a fully occupied building on a 100F day.

The solution for me was thus pretty simple: the biggest Mr. Cool “Universal” combined heat/cool system, which I started conveniently seeing Google ads for everywhere once I started my research. This beauty is good for about 60,000 BTU of both heating and cooling, which could also be expressed in the even more archaic form of “5 tons”

So I bought the circled option above. In my case, I placed the order through Home Depot website, with the free “ship to store” option, but you could also try your local Lowe’s, Alpine Home Air is good, and Ingrams now sells this unit (including the required 25 ft lineset) through Amazon.

Step Two: Remove your old furnace

This part was pretty easy – except carrying this old block of iron out of the basement.

Safety tip: Make sure you turn off both the gas and electric supply to your furnace before messing with it, as well as opening some windows and running a fan to clear out any remnants of gas as you disconnect pipes.

But once you have it safely disabled, it is as simple as carefully un-wrenching, unscrewing, and cutting away parts of the old furnace (while carefully preserving your existing ductwork) until you have the old one fully removed. You can sell or give it away on Craigslist, or drop off for free at a metal recycling facility. 

Farewell old furnace, may your steel find a fun new life somewhere else.

Step Two: adapt the ductwork as needed

Top Left: an output air adapter box I made to channel the air out to the right places. Right: A prefab filter/input box I bought off of my neighbor (who is also a builder). Bottom: You can see where the two things fit into place along with the horizontally installed heat pump air handler.

If you’re lucky (the old furnace and new heat pump are almost the same size), this step will be easy. You just connect the return ductwork to the bottom of the machine, and the supply ducts to the top. However, I was not lucky.

Because our basement ceiling is so low, I had to install the heat pump horizontally (it is designed to allow this), and then build some adapters to allow the air to flow the way I needed. On top of that, most of our ducts were falling apart and poorly shaped and useless – so I repaired or replaced a bunch of them while I was in the process. This took a lot of work, but my biggest allies were a huge roll of wide, reinforced silver tape, and simple sheet metal tools like shears, angle grinder, self-piercing screws, a good breathing mask, headlamp and work gloves.

Here’s yet another adapter I made to channel some of the air supply. The curvy box below was salvaged from the old ductwork, but I added the end cap and two 7″ air outputs to break this stream of air off to serve two different parts of the building.

Step Three: Fit in the new heat pump

Duct fitting in progress. Okay, I admit this is looking a bit patchy, but it works great! Work like this is a tradeoff between time, cost, and beauty. Since this is in an old building that is probably going to be demolished and replaced with a luxury mixed-use apartment complex when we sell it, I try to keep things functional but simple. In a high-end, permanent house, you’d take more time to make the ducts pretty.

Aside from the fact that the thing is heavy (ours was around 250 pounds), this connection is surprisingly easy once you have the ducts ready. You just screw and seal the sheet metal boxes to the bottom and the top of the heat pump. And at this point, you should be getting excited because the end is in sight.

Step Four: Place the Outdoor Unit Where You Want It

Since the outdoor unit is another 300 pounds, you’ll want a high quality dolly and some ratcheting straps, as well as a strong friend nearby to help you wrangle it into place. Your goal is to put this thing somewhere beside your house that is out of the way, but also close to wherever you just put the air handler in the basement. Then you need a lineset that is long enough to connect them together – and shorter is generally better for both cost and performance reasons (we used a 35 footer). 

We put our condenser on a couple of sturdy, level concrete pads.

Step Five: Run the Lineset

You need about a 4″ hole in your house in order to feed through the insulated lineset. Since our building is made of brick, I needed this crazy masonry core bit – hopefully yours is easier! NOTE: this is an in-progress pic, later I covered these lines with a protective steel box.

The lineset is a pair of flexible copper tubes that are wrapped in insulation. They are bulky, so even our 35-foot set came in a BIG roll the size of a big-screen television box. You need to carefully unroll and straighten it, and feed it in through a roughly 4” hole you drill in the side of your house so you can connect the condenser outside to the air handler unit inside. 

We had the added challenge of having to punch through an eight-inch-thick BRICK WALL, so I had to spend some good workout time wrestling with this massive concrete core driller, mounted to a high-torque low speed drill.

Wrenching on the lineset before releasing the gas (and then testing for leaks). There are just two nuts at each side of the line.

Once the lineset is in position, the connection is refreshingly easy: you carefully follow the instructions to tighten on the right nuts with a wrench, open some valves with an alan key, and you will hear the refreshing PSSSSssssssshhhhh as the refrigerant is released into the system. (This is the part that an HVAC technician would normally have to do, Mr. Cool gets around the issue by using special valves and having pre-charged linesets. More expensive, but very much worth it for the time and labor savings!)

Final Step: Run the Electrical Wires

Drilling a hole for the electrical wire (which we ran in a conduit, the new 40-amp breaker, inside unit wiring including thermostat, Carl celebrates completion of the outdoor unit wiring.

This will vary depending on the system, but ours called for the following wiring, which I subcontracted out to my partner Mr. 1500:

  • A 40 amp / 240 volt circuit to the outdoor unit (which simply means running a length of 8 gauge wire and adding a 40 amp breaker to the box).
  • A 20 amp / 240 volt circuit to the main unit
  • Standard six conductor thermostat wire between indoor and outdoor units
  • And finally, a run of the same thermostat wire between the indoor unit and your thermostat. We took the opportunity to upgrade to the super-lovely Ecobee Lite smart wifi thermostat, which I now use (and love) in all my projects.

The Victory Lap: Fire It Up!

It’s Alive!

We cranked through all of these steps carefully and then flipped on the breakers with great fanfare: SUCCESS! – The Ecobee lit up and started guiding us through its setup screens. Once complete, we slid the desired temperature way down in hopes of experiencing some much-needed Air Conditioning on this hot July day.

And nothing happened. We ran out to the outdoor unit and found it was just sitting there, with LEDs illuminated but nothing else happening.

We both started sweating bullets. Had we made a foolish mistake and bought a faulty unit? Did we screw something up in the install?

Nope – it turns out there is simply a three-minute delay between that first activation and the time Mr. Cool starts his cooling. Very slowly and with great grace, the big fan blades began to rotate, graaaaadually speeding up, with the hum of the compressor so quiet in the background that I had to press my ear up to the thing just to verify that it was really working.

But boy was it ever working – we ran inside and found that that icy cold air was just blasting out of each of the seven large vents spread throughout our building, and baking hot air was now shooting out of the outdoor unit. We had instantly beat the summer heat and everybody inside raised a cheer to this new luxury.

Epilogue, Three Months Later: How Well Does It Work?

A scene from The Extraordinary Event, a weekend-long set of talks and classes featuring Rebel Business School founders Alan and Katie Donogan. Videos coming soon on my Youtube Channel!

Throughout the rest of the summer, we have had a lot of fun putting this system through its paces, and it has proven itself to be an incredible cooling machine. We had several events with over fifty hot bodies packed in for some of our entrepreneurship and social gatherings while outdoor temperatures were in the 90s – and we were able to maintain comfort effortlessly.

The next test will of course be the winter. Here in early October, we have just turned the corner where the building has required just a bit of heat to start some mornings. With a few taps on the Ecobee phone app, I was able to flip the system over to heating mode and give it a whirl. It worked great – heating the building quickly and quietly.

But I’ll update this article over time as we move through cooler seasons. I expect it to continue to perform just great – but it will be fun to verify and reassuring to skeptics out there once we see it with our own eyes.

Extra Cool Detail: How Much Electricity Does It Use?

Screenshots from the Emporia energy tracker app

Of course, being MMM I was not content to just sit back and soak in the cool breeze of accomplishment just yet. I needed one final bit of data – a record of just how much energy this heat pump was sucking down in both heating and cooling modes, so we can get a better estimate of how much money it is saving us over the years. 

So I installed a system called the Emporia Energy Monitor into the circuit panel, which is currently the best value on the market for such a well-designed gadget. This allows me to track and record the full details of the energy flow – through every circuit in the house if I choose to do so. For now, I just have it watching over the heat pump.

What I found is that in cooling mode, the Mr. Cool uses about 2600 watts on an ongoing basis (about the same as two large window air conditioners), which translates to 26 cents per hour of electricity. On the hottest days with the most people, I found the system ran about six hours, meaning our peak electricity use was only about $1.50 per day!

To me, this was pretty remarkable – this was a 95 degree day with 50 people in the building, roughly equivalent to trying to cool a mid-sized restaurant in Texas. Yet even if we repeated this extreme situation every day, we’d rack up an air conditioning bill of only about $45.00 per month!

I found that the heating mode was a bit more thirsty, with consumption at 4000 watts, or 40 cents per hour. Based on my earlier estimates of heat loss on the coldest possible days, we could be in for about 18 hours of runtime per day, which would be $7.20 of electricity. So, if the Headquarters were moved to an extremely cold climate and plunged into neverending 0F / -18C conditions for an entire month (which would make it colder than Duluth Minnesota or Ottawa Canada), we’d still face a heating bill no higher than $210 for the month. But in more realistic conditions for Colorado, we would expect about half of that level of energy consumption. And of course this is only for the month or two of our short cold season. For the rest of the year, heating is even easier.

Conclusion: Heat Pumps Are The Bomb

So there you have it: we dreamed about it for years, finally did it, and I could not be happier. It is such a joy to not even have an account with the gas company, and to know that this part of our expenses will be zero, forever.

And of course it’s even better to know that even the electricity cost numbers in this article are just for your own comparison – in reality, we make more than enough solar electricity run this whole thing for free just from the pretty squares of black glass on the roof. Free heating and cooling for life, with no pollution (with free operation of our laptop computers and beer fridges, and free charging of our electric cars to boot) – This truly is the way of the future!

In The Comments: Do you have any questions about heat pumps or other home efficiency products? And if you have a heat pump of your own, what do you think of it?

  • Austin Perdue October 6, 2021, 5:15 pm

    I’m surprised you didn’t go with a more efficient unit. I looked for a long time at Mr Cool units, but ultimately went with a Fujitsu with notably higher efficiency ratings.

    • carl October 7, 2021, 5:07 pm

      The system we installed is ducted and these seem to be much less common than mini-splits. I googled and I don’t think Fujitsu offers a ducted solution. Please point me in the right direction if I’m wrong here.

      • Efficiency Hobbyist October 8, 2021, 7:39 am


        They all have different names for the ducted units it seems.

        • carl October 9, 2021, 8:15 am

          Whoah, how did I miss this? Thanks so much!

          Unfortunately, they don’t sell direct to consumer. I’d be willing to work with a contractor, but none in my area support a ducted installation.

          However, it seems like heat pumps are about to have their moment. I’ll bet that we see more old-school HVAC guys coming around this decade.

  • Denise October 6, 2021, 8:47 pm

    Great Article MMM!
    I am a relatively new reader, although I have been doing some mustachian things for a while….without knowing it. Like my partner and I decided to build our own house due to ridiculous real estate prices (I am from Vancouver, but we are building outside of Kelowna). One thing I haven’t seen mentioned is how much more efficient your system can be with energy modeling software. When you have that in hand (and I am sure you could do it yourself being MMM!) you can figure out how big a unit you need without waste. Then, get a blower door test, especially for a remodel. Hard to DIY this, but usually not super expensive, and often comes with a substantial rebate. When you do this, take a smoke stick or an infrared camera and find out where all of the leaks are, and plug them ASAP! When you have even small leaks in a building you have major heat/AC loss, and you want to optimize this!!!!! We are installing a heat pump heater/AC unit, and a heat pump water heater in our house – it is super-insulated to BC step code 5. https://energystepcode.ca/
    (Net Zero ready). We will gather data on how much electricity we use for 1-2 years, then use this to right-size our solar array. My partner is a carpenter by trade (now an inspector) and a certified passive house tradesperson. Passive house was too extreme for us – not enough optimization at the very end of the energy spectrum. But they do have some great online social events and learning resources for energy efficiency. Our house was actually featured on the build show Canada. It’s not super long, but feel free to check it out if interested: https://www.youtube.com/watch?v=Q2efBqjmhNo&list=PLbyOS-KdVjwsNeDd8LMebiKuoSQ3Hfj9f&index=6

  • Ken Dart October 6, 2021, 11:45 pm

    Since you use ecobee, you should try the add-on beestat app. It could really help you get the most out of your new system with its analytics of your usage vs weather.


  • Matthew Bochnak October 7, 2021, 4:34 am

    I have a 1 hour long step by step video tutorial on installing a MR COOL unit for those who are interested:


  • Lamont Cranston October 7, 2021, 6:21 am

    A general question to Pete and anyone that can answer.. Why does the heat pump draw more current when it is heating vs cooling? As I understand heating just reverses the cycle, so why does the compressor draw more current? I understand it may run more time while heating, but Pete said the power is higher 2600 watts vs 4000 watts.
    The obvious answer would be the emergency electric heating coils are energized, but I doubt that because it wasn’t mentioned and it wasn’t that cold out that the coil would need to be energized.

    • Mr. Money Mustache October 7, 2021, 12:44 pm

      I’d like to know this answer too. There are NO emergency/auxiliary heating coils on our system, so that would not be a factor. However, the system does have a DC Inverter variable-speed compressor, so it may well simply be running itself more vigorously when gathering heat than it does to handle cold. I am also wondering if it will go even higher when the weather is truly cold. Only a few months to find out!

      • Efficiency Hobbyist October 8, 2021, 1:21 pm

        Most will increase the compressor speed to meet higher loads. Cooling involves a smaller lift because the outdoor air is closer to the temp leaving the blow (say 100 degrees max outside and 45 leaving the coil) vs. 100 degrees leaving the coil with outdoor temps of -20 during the winter.

  • Mark October 7, 2021, 7:29 am

    You mentioned being a tradesman. I most certainly am not, but after watching several videos on MrCool mini splits being installed, I ordered one. The lazy part of me got an HVAC guy to give me an estimate so all I would do is write the check. He wanted $5650 to install a SEER 22, 12000 BTU, which I bought and installed myself for just under $1600 including pouring my slab to put it on. It wasn’t that hard and it works just fine.

    • Mr. Money Mustache October 7, 2021, 12:42 pm


      And also, WTF!? Is that number correct? 12,000 BTU is equivalent to the output of pnly a single window air conditioner, definitely not worth paying $5650 for.

      But with your new skills, you can now add affordable heating and cooling to this and all future houses, and help your friends do so too. So I’m very happy to hear you took the plunge!

    • Stephane February 26, 2022, 2:12 pm

      Oh lolz. I’ve done that too… Call them and ask them what they’d install, or even get an estimate… and do it myself. If they’re installing it, it must work reasonably well..

  • Joe Zlotek October 7, 2021, 7:36 am

    I’m not sure what refrigerant your heat pump has? You got the unit from a home improvement store.
    Don’t you need a license to buy that type of equipment?

    • Mr. Money Mustache October 7, 2021, 12:40 pm

      Like most modern ACs/heat pumps, this machine uses R-410A, which is the not-too-harmful kind. I think you still have to get an easy-to-get refrigerant license if you are doing manual pumping and filling of standard linesets. However, since these DIY kits feature pre-charged linesets, it is not necessary. More on the Mr. Cool website here:


  • Jen October 7, 2021, 8:12 am

    I am curious how easy the heat pumps are to service and maintain. We had an HVAC contractor out just yesterday as we want a mini split for a bonus room that only has baseboard heat and no air conditioning. His main concern was that each manufacturer has proprietary systems and they can be difficult to service. I’m wondering how valid this is if anyone has experience to share.

    • Mr. Money Mustache October 7, 2021, 12:37 pm

      Yeah, that is definitely a valid concern. I think that the bigger/more expensive and more widely sold an item is, the more important it is for it to be serviceable/repairable and not just disposable.

      From my own experience so far (and reading their user support forums), Mr. Cool seems like a well-run company that actually supports what they sell, and can ship you replacement parts if you need them. Carl (Mr. 1500) made a couple of calls to their tech support and was surprised to get real, detailed technical answers right away.

      The stuff is also very simple in its layout, so it looks like it would be easy to swap a control board, blower/compressor motor, etc. if you really needed to.

      Meanwhile, if you buy a $400 mini-split system from a random Amazon seller, there is a lot less chance of easy repair. It can still be a good gamble though: if you start with a low initial cost, easy install, and a relatively high probability of it being reliable (as most manufactured things have these days), it’s okay to take the small risk that your experiment will fail and you’ll have to try a different brand/machine for attempt #2.

      As I often say in these blog posts: thing of EVERYTHING as an experiment, and the two possible outcomes are “Success” and “Valuable lessons”. It’s really not a big deal, even if you make mistakes sometimes.

  • Miguel Hughes October 7, 2021, 11:30 am

    Pretty awesome!
    free heating & cooling… does really feel like a movie from the future where energy is free and plentyfull.

    I thought heat pumps where the ones that actually have a coil that does the heat exchange into the ground instead of to the air, like the one frugal touque installed some while ago.

    BTW I’m seeing some images not loading. anyone else seeing this? the one for “Step One: Pick a Heat Pump” and the one for the Rebel Business School event .

    Thanks writing this! I hope this continues to spread the idea of efficient lifestyle

    • Stephane February 26, 2022, 1:57 pm

      There are at least 3 kinds:
      1) Extract heat from the air
      2) Extract heat from a nearby body of water (sufficiently big river or lake)
      3) Extract energy from the ground that doesn’t get all that cold (below the frost line) – a much longer line is needed here. If you don’t have enough ground to do it horizontally, you have to go down, and that costs a lot.

  • European_Frugalist October 7, 2021, 9:40 pm

    I’m not sure about weather during winter in Colorado, but here – around 50degrees north in Europe – is photovoltaic near useless during winter. It can cool you in the summer, help with heating during spring and fall, but the power output during winter is too small, because of cloudy sky.

    You can suck air to the outside unit through long underground pipe (it may be plastic one). The air will be heated up a bit from the surrounding soil during winter and cooled down during summer. It’s using Earth as thermal accumulator.

    And if you’re in Europe, you can ignore all those BTUs ang AWGs and things like that. Power, heat and energy is rated in Watts (kW, kWh) for electricity, motors and heaters together. Cables are measured in mm^2 (milimeter squared) – use about 6-8 Amps to one mm^2 of the copper unless the cable is in some thermal insulator (styrofoam, rockwool, wood, etc.).

    • Alistair Twi October 13, 2021, 1:48 am

      Brussels is about 50 degrees north and that’s plenty warm enough to use a heat pump , and will still generate some solar energy

      The point about the heat pump is that even if you aren’t using solar power to get the electricity, it’s still more efficient that normal electric heating by a factor of 3 or 4. and if you live in a country which is reducing its reliance on coal and oil to generate power then it’s going to be increasingly green over its lifespan.

      I think most of sweden uses heat pumps for heating.. for example

    • Stephane February 26, 2022, 1:55 pm

      If you have net metering – and Google seems to say yes – it doesn’t matter that you don’t produce any power during the winter. The surplus during the summer should carry over to the winter. The fact that the grid has to make up this power is not your problem, not yet anyway.
      We have heat pumps in Ottawa, Canada, and it’s probably colder here than there. The only difference might be insulation (probably have more here), but you can make up for that, and it will help regardless of your heat source.
      I read an article from Passivhaus installers that they were kinda giving up on the underground air pipe – it produces the wrong temperature too often.

  • Biggsie October 7, 2021, 10:30 pm

    I love this. I’ve been watching the promise of heat pumps for years. We just bought a place in Tahoe complete with a 20 year old propane powered furnace (and 40 year old water heater) and thought, wow, this is a perfect time for a new heat pump!
    I simply don’t have the time to do this myself and calls to heating professionals were met with blank stares. I love this not-at-all-new tech but finding someone to do the work is impossible (though, I could probably get a coal furnace installed in about 20 minutes. Love ‘merica.)
    Will likely suffer with propane until it breaks down and then move to natural gas. Love that you figured this out though — and excellent write up! I might just send it to some local HVAC guys!

    • Efficiency Hobbyist October 8, 2021, 7:46 am

      There’s zero air conditioning in Lake Tahoe? Those are the guys to talk to, not the heating pros. Manufacturers often have special certifications for some installers, so try the manufacturer website (Carrier, Mitsubishi, Fujitsu, Trane, etc.).

      • Biggsie October 12, 2021, 12:48 pm

        Thanks for the tip!

    • Kristel October 20, 2021, 10:28 am

      Seems that HVAC installers everywhere charge completely insane prices for installing a heat pump – which is why I purchased a DIY Mini-Split system, and installed it myself with the help of an electrician friend. You can google any number of youtube videos on installing these systems and see the whole process, it really truly is very easy!

    • Stephane February 26, 2022, 1:49 pm

      It’s not that much better here in Ottawa (Canada) despite there being a federal grant for heat pumps. I had one try to make me worry about the cost of the electric heat backup (maybe 6 times it came on for a few minutes this winter), and they had no idea what they needed to sell me even and had to amend the quote. Most places didn’t even offer them.
      I finally found two different models – one for Mitsubishi (seems like an awesome unit) and Carrier (doesn’t seem to work so well in the extreme cold) so I went for the Mitsubishi Zumba, it seems very good so far.

  • Tyler Tervooren October 8, 2021, 8:39 am

    Fun read. Did the same project at my house a few years ago, but bought a Mitsubishi system after being convinced by numerous HVAC techs that they were built better than the rest of the industry. 3 warranty parts replacements later, I’m not so sure!

    If I could do it again, think I would go with Mr. Cool, just like this so there’s no need to hire tech to purge lineset. Mitsu proprietary controls are also awful. Think I paid $350 for their thermostat and it feels like it’s from the 90s and doesn’t do half of what I thought it would.

    One fun thing I did learn on this project is that most heat pumps have different cooling and heating capacities, so I bought a 3.5 ton unit that actually does 4 tons of heating. Where I live, that allowed me to size the heating big enough to totally do away with electric backup without oversizing the A/C.

    • Stephane February 26, 2022, 1:44 pm

      I got a Mitsubishi Zumba this December, and the unit has been working flawlessly so far, but now you’re making me worry! Still, warranty repairs are much better than no warranty. But I have to really agree – their thermostat is a total piece of junk. It’s apparently their top of line product, but it feels like some cheap flimsy product. It does everything I want, well almost, I wish I could force it to not use the backup electric heat, and what is it with the temperature scheduling has to be in 1C increments (but we can set the temperature in 0.5C???). We need to complain more to Mitsubishi.

  • Jason from NZ October 8, 2021, 2:00 pm

    I’ve had a few North Americans and Brits over the years complain about the heat pumps we have sticking on our walls in most NZ living rooms. It’s really great to hear that maybe we got it right and those big central heating systems aren’t as efficient as they make out. Most of our electricity here is hydro and wind. If anyone from NZ is reading this, we switched to OurPower in the Waikato a few years ago and our bill is never over $40 a month even in winter.

  • John October 8, 2021, 8:35 pm

    Hi MMM,

    I was looking at the specs on the unit you purchased and I’m curious – on the website it says Min/Max Outdoor Temp for Heating 22°F-75°F

    But under the features it says: 80% BTU output at -4°F outside temperature

    Do you know where one has to look to be certain that this work in temps around 0 degrees Fahrenheit?


    • Alistair Twin October 13, 2021, 1:35 am

      essentially the heatpumps become slightly less efficient as the difference in temperature between inside and outside increases.. so if you are expecting -4F then you would just have to oversize the system to account for this.

      Or add some other source of heating to help on these extreme days. like IR panel heaters or resistive heating.

  • Eric Peterson October 12, 2021, 1:05 pm

    Interesting article.
    However we have a) a “high-velocity” AC installation, one that uses small ducts that fit in a wall cavity, and b) a gas boiler for heat.
    I don’t think there is a heat pump product that would work with either of these configurations.

  • Alistair Twi October 12, 2021, 3:55 pm

    simply because nobody has posted it, this is an excellent technology connections video about heat pumps and why they are awesome and how they work https://www.youtube.com/watch?v=7J52mDjZzto

  • PeterB5377 October 12, 2021, 4:57 pm

    Hola MMM,

    What are your thoughts on the concept that was recently announced, City of Telosa, which aligns to your overall mindset with regards to simple green living?

    • Mr. Money Mustache October 15, 2021, 9:55 am

      I’ve read their little promo releases/videos so far and I like the idea so far! Will definitely be keeping an eye on the project to see if it really happens.

      Meanwhile, check out Culdesac in Tempe Arizona – it’s smaller but it’s real and getting built RIGHT NOW. (and they have big plans to make entire cities in the future)

  • James Sobieski October 15, 2021, 8:29 am

    So glad to see some real usage numbers on a Mr. Cool install. A few years ago, Mr. Cool did an install of their 2/3 ton Universal system in Grand Forks, ND on a 1940s home of about 1500 sq ft. It performed wonderfully but in the YouTube video you briefly see their electric bill was 2200 kW-hr (!!!). Here in metro Detroit, nat.gas is very cheap (.87/ccf) and electricity is pricey (.14/kW-hr). Nonetheless I eventually want to add solar to our 1952 brick bungalow (1381 sq.ft) and replace our nat.gas furnace with a Mr. Cool 2/3 ton. I think a lot of people get a nasty shock when the summertime delta-T (what, 20 deg?) shifts to winter and now you’re looking at 50, 60, maybe even 70 degree delta-T across the envelope; stands to reason you’re gonna be running harder.

    I’ve been following your stuff for a couple of years now. Currently shoveling out of debt, building some investments and then yes, I’ll have the funds for this. In the meantime we run gas, keep it at 62 and wear a sweater. Keep up the good work!

    • Stephane February 26, 2022, 1:39 pm

      We have similar electricity price (.12kWh) and similar bungalow (1000 sq feet), but I suspect our natural gas is much more expensive (I think someone had figured it was about 4 cents / kWh, which is not the measure you usually use for natural gas, but the conversion can be done). The cost to heat with my high efficiency Mitsubishi Zumba was about the same as the natural gas furnace, perhaps cheaper now that gas has gone up.
      The Zumba is a pretty expensive heat pump though, so if being frugal is the goal, it might not be the best, but it does appear to be a very performing heat pump.

  • Mr. Frugal October 15, 2021, 8:52 pm

    Is there a viable heat pump solution for really cold climates – places like Alaska where you might see temperatures well below zero for weeks at a time – or has the technology just not progressed that far yet?

    • Stephane February 26, 2022, 1:34 pm

      Tough question to answer without knowing all the details or knowing someone who has done it. But from the point of view of carbon emissions, it’s very clear: A heat pump will significantly reduce your emissions.
      My aunt had one installed in combo with her gas furnace in Winnipeg (where temperatures do dip to -40C / -40F) and hers is setup to stop at -15C and then the furnace takes over completely. So your best bet would be to look at how many days need heating and are above -15C, likely that’s a lot of them – those would be the days you save on. Assuming you’d get 3 kWh of heat for each 1 kWh of electricity.
      If you install a more performing unit, and have really good insulation, you may be able to get to -20C, -25C, maybe -30C. The more performing units (such as the Mitsubishi Zumba) cost a lot more though.

  • Stephanie October 18, 2021, 8:36 am

    Hi all! I am about to make an offer on a condo in a new construction building. The offering doc says “Cooling and heating of each residential unit shall be provided by VRF heat pump split system.” Is that the same type of system MMM installed? I was previously in a building with steam heat that never provided even heat throughout the building, was plagued by water hammer and similar issues, and definitely wasted tons of fuel due to prior owners installing a too-large boiler, so I am very attuned to our next place having a modern system that I hope will be energy efficient, quiet, and work really well! Any thoughts or advice would be greatly appreciated for this non-trades-gal :)

    • Mr. Money Mustache October 18, 2021, 11:38 am

      Hi Stephanie! Yes, that sounds like a modern setup – VRF just stands for “variable refrigerant flow”, which means the machine can adjust its heating and cooling speed to meet the temperature conditions – hopefully to run more efficiently.

      The Mr. Cool system we used is described as “variable speed”, which I *believe* is the same thing, although I’d love for someone else to chime in here. From my understanding, the word “inverter” means it uses a more efficient type of power supply and motor (DC in this case), which allows the motor speed to be smoothly controlled. If this includes the compressor motor as I think it does (as opposed to just the fans), then Mr. Cool would be VRF as well.

      Anyway, I’m glad to hear your new home is using a heat pump!

      • Marcus Hay November 24, 2021, 8:11 pm

        Hi all. MMM, you are partly right in your explanation.The term Inverter refers to systems with variable speed compressors, that are able to vary the refrigerant flow to match the cooling or heating requirement. Some of these will have variable speed indoor and outdoor fans, but not all of them.

        A VRF or VRV system also uses an inverter compressor (or multiple compressors) in the outdoor unit, coupled to multiple indoor units via a refrigerant piping network consisting of one lineset running inside that branches off to each indoor unit. VRF systems can go up to very large sizes, 50 Tons and more.

        There are also systems called multi-splits that also use an inverter compressor. There are two general types. Multi-pipe systems have a separate lineset running from the outdoor unit to each indoor unit. Branch box systems have one lineset that runs indoor to a branch box and from the branch box multiple linesets run to each indoor unit.

  • Kristel October 20, 2021, 8:37 am

    MMM – I am slightly concerned! First – I love it that you finally installed a heat pump! They are AWESOME! But…unlike a resistance or fuel-based heater, their efficiency & BTUH output is not constant, it varies with the outside temperature – I hope you took the following capacities into account when you sized the unit!

    https://hvacdirect.com/hvac/pdf/mrcool-universal-operation-limitations.pdf – your unit I believe is the last one shown.

    It could greatly help other readers if you would include a graphic like the above linked one (or sometimes I’ve seen them in a pleasing graph format) directly in your post, in case any of them follow suit in getting a heat pump! It’s critical to consider not only the peak unit output of your particular unit, but also the output at the “typical” high & low outside temperature points, and at the extremes.

    I’d wanted a heat pump for a long time, bought a MrCool DIY unit a few years ago and FINALLY got it installed (me plus an electrician neighbor) this past January. I intentionally ‘slightly’ undersized mine; by my estimates there are probably about 5-10% of the days most winters, where I’ll have to also burn a fire in my wood stove. Which is fine, because I love the wood stove anyway, and we have enough power outages that keeping it was necessary regardless.

    • Mr. Money Mustache October 23, 2021, 2:58 pm

      Yep, I certainly did take this into account Kristel, and we will be fine because the Boulder area of Colorado pretty much never gets below 0F. On an *average* basis, the coldest average daily high here is 43F / 7C, in early January. So we will definitely see high electricity consumption during the coldest cold snaps of the year, but the unit should still keep up.

      Also, thanks to the link to that useful chart. It provides more information on the efficiency at different temperatures than I had earlier – will add it to the article.

    • Stephane February 26, 2022, 1:28 pm

      Wow, that’s a nice chart, wish I could have found that for the systems I was considering last fall. I was lucky if they said anything about -15 C, never mind the -30 C on this chart. I don’t understand why there isn’t a legal requirement to show such performance numbers.

  • Doug October 22, 2021, 8:44 pm

    I live in Ontario where it can be quite humid in the winter, which can cause the outside evaporator coils to ice up. If the temperature is above freezing, it can be solved by stopping the compressor briefly but keeping the fan running. If the temperature outside is below freezing, it will require reversing the cycle periodically to defrost the coils. Wouldn’t that significantly reduce the efficiency? For conditions of high humidity and below freezing, I wonder if it would be more economical to use a backup like gas or resistance heating.

    • Stephane February 26, 2022, 1:24 pm

      I can’t say for where you are, but my Mitsubishi Zumba works fine in the Ottawa cold. I didn’t really notice much difference between when it is defrosting, but it seemed to be more related to the amount of heat it had to move than the humidity outside. While it is defrosting it shuts off the air circulation, and frost can be seen rising from the condenser outside… it’s pretty short, maybe 30 seconds. Of course this affects the efficiency but I believe it’s taken into considerations in the calculations. I have electricity usage monitors hooked up to the heat pump and electric backup heat, and I also have temperature sensors in the ducts, but since I don’t know the airflow I can’t really calculate the efficiency. I do know it cost about the same to operate as my high efficiency natural gas furnace, but now I don’t have the connection charge.
      When the temperature dips below -24C the electric heat will come on every so often to keep the house warm, but it’s not a lot. We’ve had some cold temperatures this year, down to -28C, although it never stayed there long, and the heat pump worked great. I highly recommend it.

      • Doug February 28, 2022, 8:38 pm

        I think you’ve answered my question. I live in London, similar climate but not as cold as Ottawa. I notice they have a heat pump with 2 separate units side by side at a bank near where I live, and the gas line is disconnected so it’s obviously providing adequate heat. It looks like the technology has improved a lot over the last 30 years. I lived in Timmins years ago, which gets colder than Ottawa, and I’d be curious to see how well one would work in such a climate.

  • Tim Matthews November 1, 2021, 3:37 pm

    Financially not sure it makes sence in the UK. Just moved to a house with an Air source. We used 400kwh last month just on the AS. 50% of our total usage. And they are about 8x the cost of gas boiler installation. And that assumes you don’t have to change out all your rads.

    • Mr. Money Mustache November 2, 2021, 2:09 pm

      Yeah, the cost situation is worth watching – mainly because fossil fuels are still so cheap that it can be hard to compete with them unless you’re efficient about it.

      In your case: 400 kWh is only $40 worth of electricity at US prices, which is not a big heating bill. But the equipment cost is a problem: there is no reason a heat pump (which is just an air conditioner) should cost much more than a gas boiler. There is a bit more copper/metal involved, but the installation is easier because you don’t have to worry about air intake and venting toxic fumes. So I hope the prices keep coming down everywhere.

  • Tom Coony November 1, 2021, 6:46 pm

    When you write an article that includes the following (chosen randomly), then you are in Dilbert engineer comedy territory.

    “Once the lineset is in position, the connection is refreshingly easy: you carefully follow the instructions to tighten on the right nuts with a wrench, open some valves with an alan key, and you will hear the refreshing PSSSSssssssshhhhh as the refrigerant is released into the system.”

    I have no idea what that means (I’m a math and computer science person), and neither do ~99.5% of the people on earth.

    I’m just going to wear warm clothes inside, keep my thermostat low, and read old MMM articles. Cheers.

    • Mr. Money Mustache November 2, 2021, 2:13 pm

      Haha, sounds good Tom!

      I agree that this is a fairly advanced home upgrade task. But at the same time, the concepts are a LOT easier to learn and understand than the math and computer science you use every day (speaking from experience since that was my degree and my former field of work as well).

      And if you own a house, it is an extremely good idea to learn how to maintain and upgrade it – so much more satisfying than being at the whim of “professionals”. They (we) do good work most of the time, but it’s hard to find a good one, and keeping them on task is like herding cats. So, next time something needs doing around the house, dig into some YouTube videos and give it a shot!

  • Steve November 14, 2021, 7:42 pm

    Inspired by this article, I am in the middle of a 2-3 ton Mr. Cool install. The air handler comes set up for vertical up flow, or horizontal left installation. However, all the metal screws (except for 4 of them) are the same size and I just started dis-assembling the air handler and moved the drip shelf for my horizontal right application. Now the next trick is building plenums to mate the air handler to the existing duct system. The other trick is maneuvering these units into position as the compressor weights 220 pounds and the air handler 150. I opted for the 2-3 ton unit not the 4-5, as some have noted, sometimes less for cooling condensation.

    With heat pump water heaters, they heat up slowly, so one trick is to oversize to a 60 gallon. You do anyway need a lot of space around these since that’s the buffer it dumps the cold into (extracts the heat from).

    Mr. Cool and HVAC Direct are a bit unresponsive, but I suppose in November they are busier than blind les****s in a fish market.

    Existing HVAC contractors in my (SF Bay) area seem offended by projects like these. There’s a YouTuber who had to call 7 of them to find one willing to run an old school line set (after he messed up his pre-charged refrigerant lines and let them leak – he noticed when his electric bill went way up). Even the supply houses here seem to want me to use the back entrance lest a real contractor see me. But the HVAC mafia here is like “well we might return your phone call, in 2 weeks, we can’t do the install for 4 months, and the price is $25,000” so I am now DIY.

    • Steve December 6, 2021, 10:16 am

      Mr. Cool has a number of videos (as do various people on YouTube) about the install. Of both the mini-split DIY systems, and the ducted air handler systems. On one of their videos, they say that the non-DIY systems are not warrantied unless they are installed by a professional. One video does not show the torque wrench for the pre-charged line-set install. And you need an open-ended wrench torque wrench (though there are adapter sets sold to convert a socket torque wrench to open-ended, and these should get you within 10%. Also one of the videos shows that there’s a coupler sold if you need to tie two pre-charged line-sets together to run more than 50 feet to the compressor. I phoned Mr. Cool with a tech support question, and it took them over.a week to return my call. They also offer support via an email form.

      • Steve December 15, 2021, 10:33 am

        A few more thoughts about the torque wrench. Most torque wrenches out there in the wild are socket ratchets. Typically for working on cars. Your local O’Reilly Auto Parts might rent them out. But we need an open-ended wrench here, and one of the lines needs over an inch in size. They sell kits to adapt socket ratchets over to open-ended, but I didn’t. find any that had this larger diameter over an inch.

        Proper open ended torque wrenches like BlackMax or Yellow Jacket brand, cost $160 – 180. Amazon has. SupplyHouse has and delivers faster. It seems like a lot for a tool you’ve never needed for 30 years and which you’ll now use exactly 8 times for this install, but there it is. This tool is pretty much mostly used by HVAC professionals.

        I suspect a lot of people just wing it. You can convert the Nm in the manual to foot-pounds. Its about 50 foot pounds, which is about like when you use a tire iron to tighten on a lug nut on your wheel. Tight. But not too tight. YouTube has videos of Guerrero Lopez installing this system. Its not the only video that does not include any torque wrench, not even a cameo. And what happened in his case was, he noticed his electric bill creeping up, which paralleled his refrigerant leaking out. So then he called. 7 HVAC pros, and the last one broke from the HVAC pro code of omerta, and installed a proper line set (Or maybe its possible to just cut and recharge the leaked out pre-charged line set). For $1400. Which seems expensive but they have to make up for how you didn’t buy your equipment from them.

        In conclusion, I know just enough now to be dangerous, but I hope this helps. Also consider the suggestion above to use Nylog Blue. And, just get 250’ of 18/8 8-wire for the thermostat. You may only use 5 or 6 of the wires, but you’re loaded for bear.

  • Nick Campion November 18, 2021, 2:55 pm

    Have you heard of a Heat Recovery Unit (HRU). Upgrade any air conditioner, large cooler or freezer, or heat pump system into a source of free hot water. My HS science teacher shared this with me. Wondering if anyone seen, used, or heard of one of these?


  • Michelle November 27, 2021, 8:55 pm

    Interesting article and comments.
    How does the heat pump differ from a VRF system? Sounds like similar technology since it’s heat exchange?
    If not the same, what are the pluses of a heat pump?
    I am currently researching a new system to install in my 1915 home that currently has a high- efficiency natural gas system that heats hot water to cast iron radiators. Heating costs are fairly low but I’d love to get away from gas.
    Does the ductless option with the heat pump require mini split units? Any options for small diameter high velocity tubing?

  • Miley November 28, 2021, 11:15 pm

    Longmont must be incredibly mild if you consider -20F “virtually all climates.” several of my coworkers and I recorded temperatures below -40F a year or 2 ago in southwestern IA. That cold snap only lasted a couple days but those are the days you need this equipment the most.

    That said, I know someone who uses a heat exchanger and their “outdoor unit” is actually a ways underground where temperatures are more steady so that set up worked fine for them even in that cold snap.

  • Erin November 30, 2021, 8:14 pm

    We installed a heat pump in March, hoping to cool our home efficiently as well. We were using a swamp cooler before so I didn’t have a basis for comparison, but between low use months and the peak of summer, the difference in our electric bill is $100, so we still spent $100 on cooling in our peak month. I was expecting better than that, but we are a family of 8 so maybe that is why.

    • Mr. Money Mustache December 3, 2021, 2:00 pm

      Yeah, in a big house / hot climate / low cooling setpoint, that could happen. But it would imply about 500-1000 kWh of electricity depending on the electric prices where you live, or 200-400 hours of runtime for a system like the one I describe in this article. In other words, the A/C would have to be running between 7 and 14 hours per day, which is definitely rare.

      When really calculating how much energy an appliance uses, I encourage people to install an actual meter instead of just comparing the use to past periods, because there can be so many other factors that change a household’s energy use as well (clothes dryer, hot tub/pool, oven, electric car charging, any non-LED lighting still in place, fridge, computers, cable boxes, etc.)

  • LJ December 4, 2021, 5:45 pm

    How does the permitting work on a project like this in your area? I looked into this myself and this is permitted project in my area–both a state and county permit is required. (My area is admittedly draconian: I need a permit to replace an interior door.) And failure to get a permit can waive your home insurance. I would really love to read your DIY guide to permitting. Frankly, I have opted against doing many home projects that I know that I could do because the permit application process seems onerous especially for the inexperienced.

  • Steve December 8, 2021, 10:48 am

    Details on connecting pre-charged refrigerant lines. Mr. Cool does say to use a torque wrench. https://www.achrnews.com/articles/137337-pre-charged-line-sets-save-time-money-when-installed-correctly

  • DS December 9, 2021, 5:52 pm

    I always thought that heat pumps got less efficient for heating as the outside temperature drops. Makes sense to me since there is less heat to suck out of the frigid air, and the HP has energy wasting defrost cycles. The way it was explained to me was that if your HP was rated to say -10, this means at -10 an electrical resistance heating element in your furnace would be equally efficient. So at my house I use my very efficient woodburner well before the outside temp drops to the lowest rated temp for the HP. What I really need now is to get that Emporia energy meter so I can measure at what temperature using wood with a continuous blower is more energy efficient than the HP.

    PS> No living trees are ever cut down for heating my house – standing dead only.

  • Grant December 10, 2021, 9:02 am

    The described setup is an air/air heat pump setup. For efficiency and comfort an air/water heat pump will be much better, so it will be more costly to install (in an existing building). You then use heated floors and heating elements where the water is circulating through.

    Much lower electricity consumption and therefore much better for the climate.

    • Mr. Money Mustache December 10, 2021, 8:19 pm

      You’d think so, but it depends on the machine and the average annual climate in which you’re installing it. If you look at the COP (coefficient of Performance) for this Mr. Cool versus a typical water-source unit, as I did when researching this setup, it’s not as different as you might think.

      Also, the money (and diesel fuel) spent on digging out a yard to bury water pipes is also a significant pollution factor as well. I’m a big fan of just pushing the technology to get more efficient with air source pumps. The easier the install (and fewer permits, less red tape, less specialized skills), the more people will do it.

  • William December 10, 2021, 1:18 pm

    I installed a Mr. Cool this summer for the second floor of my house in Seattle, which used 230V Cadet wall heaters previously. One thing to keep in mind is that if you install the air handler inside (anywhere other than the basement), you need to drain the condensation (when it’s running in a/c mode…as others have noted the outside unit condenses in heat mode). The main advantage of a ducted unit over mini split for me was that it’s really hard to make water go uphill, and each air handler requires a condensate drain. In my house it wouldn’t even be possible to put them on exterior walls. A ducted unit can also be useful in a situation where there are some very small rooms and very large rooms since there’s more flexibility.
    Also, if you’re installing one of these systems, be sure to buy a long enough lineset to allow for a really large radius bend. It’s possible an HVAC professional could get the lineset to bend to the 4″ minimum radius from the documentation without kinking; I could not. So even though my inside and outside units are 35 feet apart, I had to buy the 50-foot lineset. Measure twice!

  • Steve December 20, 2021, 10:58 am

    On family vacations to NYC, or Taipei, or other cities with skyscrapers, I like to take my wife and kids to the observation deck of tall buildings. We marvel at the view, and I point out the houses, buildings, roads, cars, bridges, wires, and the millions of people they support. And then I say, a little loudly, “Remember kids: all that you behold was built by men”. Today, I’m feeling my oats as a man, having got my heat pump working and keeping my family warm, in time for Christmas.

    This project was definitely a degree or two of difficulty beyond assembling IKEA furniture, in size, depth, and cost. Its not one thing, its more that there are many little details to the project, for which you are often on your own. You need faith, perseverance, braun, brains, and Google.

    I’ll mention a few of those details, but let’s start in general with Mr. Cool. My estimation is that their business model is, to patent, manufacture(?) and sell their pre-charged line set invention. As part of a larger plan as one of many importers of the Midea HVAC gear manufactured in China. As such, they’re in for spending money on sales (to distributors), marketing, and support. (Some say Midea is pretty solid, and used by Carrier.)

    In the end I found Mr. Cool support to be lacking. They need more videos on YouTube. They need to have and actively manage an online support forum. As it stands, they seem overwhelmed and engaged in triage for the support demands. I put in a ticket and its been 2 weeks without a reply. Calls to support go to voice mail. I called several times and it took over a week to get a return call. Finally I stumbled on one employee’s email while Googling, and he helped by sending me the wiring diagram. In other words, they are relying on Midea installation manual. There are several places where Mr. Cool really needs to add detail.

    Some people and some videos wing it, but I bought a proper open ended torque wrench, and these are $160+. That got hung up for a few extra days by UPS. Meanwhile Fedex sent my pre-charged line set around Cape Horn and that took an extra week. Meanwhile temperatures are dropping. (I heard FedEx and UPS are merging… new company will be called Fed-Up). (Amazon delivers more reliably, they will put FedEx out of business one day, mark my words.) Note though that when you crank the torque on the line set adapter on the (Universal, not the mini-split) condenser unit, you can end up bending the mounting bracket.

    With the refrigerant lines, I went with a few strategically placed drops of Nylog Blue. No POE oil, and definitely no teflon tape. The A/C wiring requirements, and the thermostat wiring requirements, really need to be spelled out more explicitly in the manual. The final fix for me, the Nest thermostat has a slightly obscure setting for *O/B. I think I set it to O and at last the heat started blowing into my cold house.

    • Steve December 20, 2021, 1:42 pm

      Also, I screwed one of these Honeywell Electronic Air Cleaners onto the air handler intake.

      Honeywell Home F300E1027 Electronic Air Cleaner, 20″ x 20″ $591.82 each



      • Steve December 22, 2021, 9:53 am

        Wanted to clarify the actual support guys at Mr. Cool are pretty um, cool. My criticism was just that over the last month or two, it takes a week or two to reach them. You get voice mail and they don’t call back. They must be busier than… nevermind… and meanwhile its getting cold enough here to make a fox sh** copper…

        At least for mini-splits, there are many brands. But manufacturers know that if they open up direct sales to the end user, they’ll alienate their existing installers and the HVAC mafia. So not many have broken rank, but here’s a second one that has https://www.pioneerminisplit.com/

  • RPC January 3, 2022, 1:07 pm

    So here we are in January 2022 – how’s the heating performance?

  • peter stock January 5, 2022, 9:56 am

    An excellent DIY reuse of the huge fan from an old decommissioned furnace is the build your own “blowerdoor” depressurizing fan for finding weatherproofing leaks in your home.

    this page (not mine) explains things and shows the commerical vesion of a fan versus the DIY vesion


    I scavenged the fan from a discarded furance and built this one.


    When you hire an energy audit company their first step is to set up a huge blower fan in your open front door. It effectively depressurizes the house so that outside air will be sucked in through any gaps and leaks. Fill or insulate those leaks and you save money.

  • Michelle January 20, 2022, 9:03 am

    Nice work – awesome to see. Can I just give a big thumbs up from a fellow home builder and happy heat pump owner from here in the UK!

    When we built our place the only options in town were electricity or oil – ouch! Being green minded we went for the heatpump even though it wasn’t very well known back then, about ten years ago now.

    We paired it up with underfloor heating and it just runs and runs. No cold spots anywhere, no hurried dressing n the morning! It’s so cheap and efficient, just love it.

    The funniest thing was we ended up qualifying for a government scheme after someone mentioned it to us after we had it up and working. Ended up getting more back than we paid for the entire thing! Crazy but good.

    I’m so pleased to see them finally getting the attention and support they deserve. They really will make a huge difference to the world.

  • kruidigmeisje January 24, 2022, 8:52 am

    Translating for the people doing SI units (The world minus VS): 100.000BTU/h is a 29 kWh heatng unit. That is a capacity for a normal family home heating unit?

    That is mindboggling to me. Here in NL most of us burn gas in a heating unit that is usually around 10 kWh (max capacity) for a family home (200m2 living area). What building materials do you use for a home over there? Sieves, tent poles and loose cloth?
    I am in the process of upgrading to heat pump, and I am getting quotes for a 4, 5 or 6 kWh sets. Which is still way oversized, once the insulation is all in our old (1928) house, but let’s err on the safe side. And yes… all the electricity for home use plus the heating will be generated from solar panels on our roof (60m2 on the ground floor), our little roof in the middle of the city.

  • Stephane February 26, 2022, 1:14 pm

    I had a Mitsubishi Zumba 2 ton installed to heat my 1000 sq feet bungalow house. It works fine up to -24 C, at which point the electric heat will occasionally assist it. So far we’ve only had -28 C, so I don’t know if it works below that though I believe Mitsubishi says it does (of course, the house loses more heat as it gets colder, and the heat pump extracts less heat, so the electric heat will come on more).
    Also, I believe only licensed technicians are allowed to modify the lines with the refrigerant, so I do believe it is possible for a homeowner to install heat pumps here, at least not the kind that can’t be preloaded.

  • Reader March 14, 2022, 6:57 pm

    After the Cold Snap that happened in February I was wondering how well the heat pump worked.

    • Dave May 20, 2022, 11:32 am

      I’m hoping for an update as well as I’m considering a heat pump and just up the road in Fort Collins

  • Flaviu May 1, 2022, 2:34 pm

    It’s surprising to see the Emporia Vue mentioned here! It’s a great device, and I’ve helped develop open-source firmware for it so that it can be brought into a home automation system (like Home Assistant)!

    Instructions can be found here if you are so inclined: https://gist.github.com/flaviut/93a1212c7b165c7674693a45ad52c512

  • Steve May 23, 2022, 7:27 am

    Video of installing the Gree unit that MrCool uses. Video uses traditional line set and not pre-charged line. https://youtu.be/ZPilWCsLcdc

  • Johnny Money July 16, 2022, 7:29 pm

    I’m about to tackle a similar project on my rental home – It’s getting really hot here in Denver! I do have a unit, undersized for this home, but that’s what I’d rather, a minimal system as opposed to arctic cold in a rental. Aiming for tolerable and sleepable, despite the weather and the climate and all that other stuff.

    Osha – positive pressure ventilation for asbestos – yes, cartridges may have ratings like P99 or P100, but that’s not counting 1/3 leakage around your face, making it likely you will accumulate a dose in your lungs over time. Without positive pressure, a p100 cartridge ( 100% particulate) is actually 66%. How do you feel about 1/3 lead paint, asbestos, mold? As little as possible, and certainly less than 1/3!
    -Water sprayed on that greyish paper they wrap on ducts reduces it’s friability, a measure of dustieness.
    -Don’t ask, don’t tell. There are legal ramifications, so choose words carefully, and think about what you are doing. A suit resulting from sloppy removal could get costly! Act with integrity. Would I live there and am I realistic in evaluating hazards?
    -Encapsulation is often a strategy, as demo raises lots of dust. Paint, humidity, water, etc will keep dust immobilized.
    -The dustier / more friable, the more likely you need a pro.
    -most old tile tar mastics also contain asbestos. Old 8″ linoleum tiles are almost certainly asbestos. Furnace linings and old attic insulation should be suspect. Grey paper around ducts, old electrical wire, etc all has the potential to be the bad asbestos. As long as it’s not airborne, zero problem. It’s your lungs.
    If you choose to tackle it, I recommend a painters hoodie tyvex suit, yellow and pink cartridges on a 3m respirator, and treating it like decontamination, don’t wear the tyvex through anyones living space, take it off after work, wash, etc. I do the same for toxigenic molds.
    -I contract out an all clear test after remediation to prove the outcome / justify the cost to clean. You can get both asbestos and mold self service kits instead of an expensive tech to come on site.

  • Doug Sprague September 26, 2022, 3:54 pm

    Great project and article, so well it inspired me to do the same, my oil furnace is now in the corner of the basement, the Mr Cool 2-3 ton universal is connected and running. It was a good project, took me a while to install and it was challenging. It is taking me a while to get used to how a heat pump works in that it is slower than my oil furnace in heating/cooling. I expected blasts of cold/hot air coming out of the ducts but its more mild than that and when the winter comes on I am hoping it will keep up. I am trying to use a Nest thermostat with this unit but I get low battery messages and wires not detected errors. Ingrams Water and Air where I purchased the unit said the nest does not work with these units. I guess I should buy an EcoBee Lite?? I have called Mr Cool support and was not able to reach anyone, voice mail circles, hopefully they will get back to me and I wont have made a mistake in buying this if I have a problem with the unit. I am keeping the oil burner in the corner in case I have to re-install it.

    • Mr. Money Mustache September 26, 2022, 9:02 pm

      Hey Doug! First of all, congrats on getting through the install. A long as your house is not too big (or in a moderate climate), I’d expect the 3 ton unit (36,000 BTU) to be able to keep up with winter. 36k would handle a fairly-well-insulated 1500 square foot house here where I live in CO.

      If you need more BTUs, you could always add a second source for the coldest days. I’ve noticed standalone mini-split systems now on the market now that look like the old mini-splits but also do heat. And they’re like $800 on Amazon nowadays – an intriguing fix for houses where only one zone might need extra heating or cooling.

      As for the wires and the thermostat: these things do have the full 6-wire setup including the C wire and all of that. Normally if you have battery messages, it’s because the C wire (24 volt supply) isn’t hooked up correctly. And there is an extra wire as well with a heat pump – typically brown, and used to reverse between heating and cooling.

      I’d expect it all to work with a Nest thermostat, but if not the Ecobee Lite has a drastically better user interface anyway (and costs less), so it would be a nice upgrade and that’s what I have used on two separate Mr. Cool installs at this point (and soon one in my own house because they work so well).

  • Tom October 3, 2022, 11:03 am

    Thanks for the wattage quotes from your Emporia and the detailed write up. Maybe I missed it but you have this configured as the 5 ton option? And the 2600w running includes the air handler also?

    Have you tried the 4 ton setting?


    • Mr. Money Mustache October 3, 2022, 8:31 pm

      Hi Tom,

      Those figures do include the air handler (1.5 – 2.6 kW in cooling mode, 2-4kW+ in heating mode depending on outdoor temperature). And, we configured the unit into 5 ton mode.

  • Brandy November 30, 2022, 10:49 am

    Can you tell me more about your solar panels? Perhaps you already address them in a separate post, so I’ll be sure to look for it just in case. How much did that cost and did you do it yourself too? Where did you buy them from?
    We lose power on occasion during bad winter storms, so currently I am grateful we still have gas for heat whenever the power goes out, but if we could rely on solar power first, then investing in a heat pump would be the next step!

  • Speqtre June 27, 2023, 10:07 am

    Hey Mr MM,

    Please update on the Mr Cool setup! How’s it working out? Any problems?


    • Mr. Money Mustache June 27, 2023, 7:40 pm

      Still working great as of June 2023! I haven’t really updated this article, but thankfully there isn’t much to report.

      I liked the machine so much that we have installed several additional ones at the homes of friends, and I’m going to do my own house soon too.

      • Scott February 2, 2024, 9:42 am

        Ah, thanks for the info mmm, i some how missed this and posted a question below.

    • Douglas January 18, 2024, 7:05 am

      I have all kinds of problems and the company does not stand by the product or warranty. Check the BBB site and you will see many of the same complaints.

  • Douglas January 18, 2024, 7:04 am

    DO NOT BUY A MR COOL UNIT, check the BBB site for reviews with a 1.4 rating, I Installed a system and the company is NOT standing by the warranty or providing any useful support.

  • scott February 2, 2024, 9:38 am

    Hello MMM, All,

    For those who are looking to DIY their own heatpump install for anyone including MMM who did, how are their heat pumps holding up. What brand did you install, when and any feedback on how its been functioning.

    Mr. Cool has good ratings on that large online retailer and seems like the easy pic.

    kind regards


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