The Radiant Heat Experiment (on a seriously low budget)

The house rebuilding project is going well. We’ve finished all the framing, and the higher ceilings and more open floorplan are hinting at a level of awesomeness that surprises even me. A picture from just this morning:


Here is the new living room and the kitchen around the corner in the back. Old ceiling height was at the bottom of that steel beam. 2 more giant window openings still to come behind those plywood squares.

While I’ve destroyed and rebuilt quite a few houses for other people, this is the first one I have been fortunate enough to create from nearly scratch for my own family, so I am treating it as a bit of a science experiment. I want to build neat energy-saving features into it, but they need to be cost-effective and homegrown whenever possible.

Any old rich guy can hire the top architect and boutique builder to make him the latest LEED-Platinum superhouse to show off in Dwell magazine… at $1000 per square foot. But with energy cheap and skilled labor and high-end home materials expensive, it takes more thought and experimentation to save energy AND money at the same time. And one of these experimental projects is to build my own radiant under-floor heating system.

If you have never heard about this, you’ll want to tune in. The dominant heating method in the US right now is the forced air furnace – a big box in your basement that blows air (and dust) through a huge network of bulky air tubes so it can reach all parts of your house through floor vents. It works, but it is not elegant: they make noise, waste a surprising amount of interior space with ducts and chases, and are a hassle to install or upgrade.

When my small construction company was building some houses from the ground up a few years ago, the architect highly recommended that we use hydronic (radiant) heat instead of forced air. “It is a world of difference”, he said, “To have that silent warmth radiating at you through the floor instead of just blowing around some hot air.”

Unfortunately, when I got quotes from some plumbers for this type of heating system, the cost was astronomical: $35,000 or more, when a full conventional heating system was only $10,000 installed. Since these homes were being built to sell, on a tight budget to compete with other houses in the forced-air price range, I reluctantly decided to skip the luxury option. Plus, the passive solar design in our architecture would ensure that the furnace was used only lightly anyway.

Now, the picture has changed. I have learned to do my own plumbing, and new technologies have come down in price that make radiant heat much more affordable. After quite a few long nights of research and online training videos, I have bought all the necessary parts and we are about to put this sucker in.

What is Hydronic Radiant Heating?

Have you ever walked past a large brick building long after the sun goes down, and felt warmth all over your body even without touching the wall? How about feeling the heat from a hot bed of campfire coals even when sitting some distance away? This is radiant heat in action: a warm surface shines out infrared light (also known as heat), which directly warms your skin. With a hot campfire on a still mountain night, you can feel completely warm even when the air temperature around you is below freezing.

This same concept applies nicely to warming a house with hydronic radiant heat: warm water circulates in tubes under your floor, causing the floor to warm up and shine heat at you from all directions. There are no ducts and no blowing dust, and the system operates silently. And because the system is warming your skin directly at the same time it warms the air of your house, you feel warmer at a lower temperature setting, which allows you to keep the house cooler, saving energy. But the best part may be that you have constantly warm feet, wherever you go in your house.

So how do we build one of these systems? In a nutshell, you need something to heat the water (sometimes called a boiler), a network of tubing under your floor, and a pump to circulate that water through all that tubing:


While the concept is simple, my summary leaves out a lot of detail. When you look at the typical “boiler room” in a luxury house, there are all sorts of valves and sensors, and miles of meticulously soldered copper from the $35,000 plumber.  I mean, shit, does this look like an easy do-it-yourself project to you?


Me neither. This is why I have always gone with forced air furnaces in the past.

On top of that, hydronic heating is an art and science unto itself, with things like ΔT, GPM, BTU/hr, and R-value calculations involved. If you can get through all that, you’re faced with boilers that start at $2000, a complicated selection of parts that nobody except the experts really understands (you won’t be getting advice at Home Depot on building one of these systems), and all sorts of other hurdles.

However, after digging through all this rubble, I found a few simplifications that bring the cost and complexity of radiant heat way down, to make it a DIY-compatible project for the average handy Mustachian. The tricks I’m applying for my system:

  1. Using drinking-water-safe components allows an “open loop” system which requires fewer valves and allows item 2:
  2. Using a single tankless water heater for both hot water and house heating cuts out the $2000-$4000 boiler cost. I chose this extremely efficient Rheem Tankless unit that runs only about $1200.
  3. A single variable speed circulator pump eliminates most of the loss and loop size calculations by sensing the water temperature and adjusting its speed automatically (this also saves energy).
  4. Using a pre-made manifold from Rifeng allows easy multi-zone control and adjustment, without the need to ever mess with the tubing after you install it.
  5. And of course, everything is done in PEX, to eliminate the cost, slow installation, and boiler-room heat loss of copper pipes.
Disclaimer: Like all of my experiments, and indeed my whole lifestyle, there is some unproven stuff in here. I am using myself as a guinea pig, and there may be some trial and error, and even risk involved. Enjoy and learn, but don’t dive in as a beginner just to follow me (another beginner) blindly!

Boiling it all down, the system I ended up with is relatively simple, and I drew it out for you in this picture:


My proposed radiant heat system (click for larger)

So far, this is a work in progress. I have already run this by a system designer and received his nod of approval, and completed some of the installation, so I am sure we can get this to work. But there are surely improvements to be made.

The great thing about this blog is that there are many people reading right now (including professional plumbers) who have already done this, so if you have any suggestions on how to improve or simplify it further, it would be much appreciated and I will update the article as new information is received. I will also publish a second post when everything is done, to show a few of the steps in progress and the finished pictures.

Reader corrections so far:

  • Add the expansion tank before the pump, not after it as currently shown
  • Watch out for Legionella bacteria growth in an open-loop system like this. While rare, the bacteria is dangerous. Exactly the same risk exists if you have a tank-type water heater and keep the water under about 120F. Solution: make sure my tankless unit is hot (legionella dies above 122F, so perhaps 130 or higher), to exterminate bacteria. Also, drain or flush the heating loops during the offseason so the water does not sit stagnant for months.
  • OR, create two-loop system with a heat exchanger in between the two loops, so the heating water never touches the hot tap water. This requires oxygen-barrier PEX and an air eliminator. You can also buy tankless heaters with two independent loops: one for heating, one for potable water.
  • Add a check valve on the 3/4″ return line so cold water cannot sneak back into the manifold instead of going to the Rheem (I guess this could happen when the pump is off)
  • Actually, add a check valve on every loop, just to make sure there are no flow surprises and water goes the direction you want it to. Otherwise, cold water can be drawn through loops unexpectedly.
  • Many tankless heaters (including the Rheem I recommend above) are not warrantied for use in heating systems. This is fine for me, as I find warranties are generally useless anyway. But it is good to note.
  • Further criticism about this experiment showed up here on the forum of the useful site called heatinghelp.com. While the thread almost convinced me that I am an idiot, the thing is that a similar discussion forms somewhere on the internet about every single article that ever appears on this blog. Many plumbers spend their days cursing this site just because I recommend doing some of your own plumbing with PEX, for example. The problem is that my fellow tradesmen tend to use anecdotes rather than statistics to make these safety decisions. The experiment will go on undeterred, but I will make a point of doing some tests with my friend who works at the city’s drinking water treatment/analysis lab.

What About Cooling?

Every house should be designed to suit its own climate. Here in Colorado, we have intense sun nearly every day but much cooler nights due to our elevation 5000 feet above sea level. So the house has loads of South-facing windows to capture heat and more loads of thermal mass to smooth out day and night temperature swings.

In the summer, this picture flips around: the Earth tilts so the sun is nearly overhead (and the large overhangs I built onto the house shade the windows from the rest of it). You keep the windows closed during the 90F days and the interior stays cool. On summer nights, the temperatures drop below 60F, so you run a large fan blowing out the day’s heat to cool everything down and begin the cycle anew.

I find this strategy (along with not being a Giant A/C Wussy) allows us to live happily without turning on our A/C in Colorado. But there’s always a backup: most modern houses without ducts use a ductless mini-split air conditioning system for cooling. These can be more efficient than central A/C systems, because you only cool the rooms where heat is building up. I will add a system like this if necessary, but we will be sure to test out a summer without air conditioning first, since the place is likely to be even more comfortable than our current house, even without cooling.

As the final cheat sheet, here is my shopping cart from PexSupply, my preferred supplier of plumbing stuff. There are a few extra things in my shopping cart for building out the bathrooms, but in general this is a complete system for a 1500 square foot house: about $1100, with free shipping and no sales tax. Add in the water heater and you have a complete heat and hot water system that costs less than a single low-efficiency furnace.


An efficiency upgrade to this system: I also purchased two boxes of aluminum heat reflector plates from Amazon which should improve heat transfer and efficiency slightly. Cost was $2.45 per 4-foot plate ($245 for each box of 100).

Update: After building the system with these, I feel it was highly worthwhile as it makes installation faster and cleaner, and improving heat transfer is a worthwhile goal with wood floors – while they work well, you do need all the heat you can get.


Update: One Year Later

This system is now up and running and you can read the results in the update article here:

The Radiant Heat Experiment – Did it Work?


  • Mary Longacre February 16, 2014, 12:04 pm

    When you’re designing your system, it will work much better if you create separate zones based on the natural hot & cool spots in your house. When I designed my home with radiant heat, I was told by the manufacturer that I only needed two zones – one for each story of the house. BAD idea! The first story had a greenhouse off the west side and a north facing ell. The heat was never on during the day in the ell because of the passive solar in the front of the house. They shouldn’t have been on the same heating zone.
    Also consider separate zones for rooms you rarely use so that you don’t have to heat them unnecessarily – but of course that’s true with any heating system.
    I loved my radiant heating system! Except for the boiler, it was a DIY project.

    • Free Money Minute February 17, 2014, 6:20 am

      Sounds like a good adjustment so you can control more areas of the house independently.

    • Mr. Everyday Dollar February 17, 2014, 7:56 am

      After dealing with a leaking dishwasher yesterday, and a leaking refrigerator (from the water dispenser) a few months ago, I have come to despise water-based issues. I love the idea of radiant heat but am curious what leak detection capabilities are available? Are they needed?

      • Roch Naleway February 17, 2014, 12:16 pm

        It is possible to do a leak test by pressurizing the system before starting it up. If the pressure holds it is all good to go. Alternatively, it is ok to let water enter the system. Get the air out by opening the hot water faucets. Close the faucets. Then run out to the water meter to see whether it is spinning. If it is not spinning it is all good to go.

      • peter February 18, 2014, 9:12 am

        Much like you, I have learned to hesitate with water. I’ve seen too many old pipes (pex even) give up the ghost in my old house. I’ve seen my “frost-free” outdoor fawcets let go all with really irritating results. None of this work that failed has been my own and I think the previous owner may have consistently gone with the lowest bidder for every job.
        That being said, I’ve often thought that if I were to build my own house I would have a catch for all potential water leaks. Drains in all bathroom/laundry room floors (like every commercial building out there). I even figured it would be smart to run double walled water supply lines as in pex inside 4″ PVC drain pipe. This system has me thinking about installing collection baffles between the floor joists as there are a LOT of joints and potential leak points in that system.
        Maybe a bit paranoid, but as someone who has witnessed a lot of water damaged rooms throughout my travels, it seems a reasonable and relatively inexpensive. What do you think MMM?

      • Leslie February 18, 2014, 1:30 pm

        Yes, there are leak detection services available and you can test it yourself. We live in a house built in 1958 with radiant heat, with water in copper pipes, heated by a boiler. We replaced the older boiler with a new tankless model. Over the years some of these systems have developed leaks–however usually after about 40 years. So far, we have been spared this problem. The solution is to install tile flooring instead of wood. That way, if there is a leak you only have to replace the tiles affected in the area where you have to drill into the slab to fix the leak. Probably, other solutions exist that I am not aware of.

        • ken February 3, 2015, 6:24 pm

          Concrete and copper do not go together very well over time and there should never be a joint in concrete

    • Mr. Money Mustache February 17, 2014, 8:12 am

      Definitely Mary.. I’m splitting the place into six zones based on my best guess of what will be different temperatures. The bedrooms are all along the North, which means they won’t get as much solar heat in the winters. The kitchen/living/dining area has all the sun and thermal mass (plus a fireplace), so it will rarely need heat.

      • Brent February 17, 2014, 12:29 pm

        More zones always sounds better, but (as you’re probably already aware) they add cost– in the three hydronic systems I maintain, the zone valves are ~$110 wholesale each. Add to that: the thermostats, wiring, and possibly a transformer, and you’ve added quite a few percent to your budget, but it’s probably still worth it from a comfort+efficiency stand point.

        One note: For some reason, I always see the pump on the return side between the zone valves and the boiler (pushing water toward the boiler instead of toward the loads). I don’t know if that is the best practice or if it is just typical practice in only my area, or what. Do you have any analysis about the pumps location in the loop?

        • Mr. Money Mustache February 17, 2014, 5:19 pm

          The cool thing about the Rifeng manifold is that you can add individual actuators (zone valves) for about $40 each. Throw in a $40 programmable thermostat for any rooms on their own zone, and you’re good to go – no transformers in the whole system (even the pump can connect to a standard thermostat).

          Note that with multiple zones, I think you’ll need to connect all of them in parallel to the pump as well as their own actuators, to form a logical “OR” function (if anyone wants heat, the pump will run).

          • Maverick February 18, 2014, 1:25 am

            You could also make your own manifold using a larger diameter copper pipe, such as 1-1/2″ dia and branch off to 3/4″ dia for each zone. This is how my radiant system is designed. I also used high reliability, multi-speed, quiet Grundfos circulating pumps; one for each zone (with their own thermostats). I’d also suggest using a larger diameter 7/8″ PEX tubing as it affords a higher heat transfer per foot (to square foot of living space above) and is a lower resistance to the circulating pump so longer lengths can be employed. I used a Polaris 97% efficient hot water tank instead of tankless. Tankless can be great for vacation houses where there are days of no use. But in a primary house where hot water is used daily, the standing loss is small with an insulated tank and the benefits of tankless will not be evident in actual operation. (Much like a turbocharged 4-cyl IC engine; there is no cost savings when your foot is always pressing into the throttle.) And never use a boiler with radiant…boiler temperatures are too high.

            Make sure that no part of the radiant system gets subjected to freezing temperatures after it is filled with water and not operational (such as power outages). You know what happens when water freezes in a radiant system, right? :)

            When you get your system fully assembled and ready to operate, your number one issue will be to get the air pockets out of the system. With this in mind, I suggest using a radiant air vent at the highest location(s) of the system. Trust me on this one point…getting the air out can be a PITA…and the pump(s) will not just push the air out. The pumps in a radiant system are to “gently” move the warm water through the tubing. High pump pressures will only encourage internal piping erosion.

            MMM, I’d be glad to share my system details/photos if you reply to me directly.

            Good luck with your experiment! You’ll enjoy radiant heat…just like the Romans.

            • Frans Slothouber December 7, 2020, 12:46 am

              Hi Maverick,
              Thanks for your posted radiant heat info.
              I’m in the process installing a system myself.
              I would really appreciate if you would share your photos with me.

              With kind regards,

          • Laurel October 10, 2014, 1:45 pm

            You can certainly use a tankless. I have for about 12 years with no issues at all. I often wonder if the Polaris would save me money. My neighbor installed a Polaris. Our houses are pretty similar, and his gas and electric bills are similar. The difference is that when my tankless unit goes out, I find it’s cheaper to replace it than to repair it. No, seriously, it is. I tried dealing with the warranty and all I ended up with was a cold house while I argued. So I replaced it and was up and running in a couple hours.

            I have replaced them twice in 12 years. That seems like a lot, but we run this system 24/7 super heavy, and keep the house super warm because of my elderly mother-in-law, and also because we work at home. It’s a large home. It takes a couple hours to slap in the new unit, the new units cost $750-1000, and it’s done. My neighbor, on the other hand, has been plagued with little burner issues on his Polaris. You can google it. I helped him once. Each repair cost more than $750 for the plumber, and he was often cold until the plumber could come out in a day or two. He learned to do them himself and always keeps a spare igniter/burner handy in case it goes out. The part itself costs $300. And it takes about as long as it takes me to do my tankless switcher. We laugh about this.

            The other issue is space. I redesigned my whole basement around this tankless to gain extra space, so even if I wanted to go with one of the high end combination boilers like Triangle Tube, or just go with a Polaris or Voyager, I don’t have the room anymore. Besides, I have never ever seen an easier thing to install, d-install, and replace as one of these tiny tankless heaters. They are the size of a backpack.

            Finally, the Polaris costs three times the tankless. If the monthly savings were significant, or it was truly greener, I would be all for it. (I drive a prius plug in.) It would be worth it. If the savings aren’t there—they are not.

            Oh, actually, this is my final point. The tankless I replaced last year, I went upmarket to the condensing model, and NOW I am saving about 15%-20% on my bills. So it’s cheaper than the neighbor’s. The condensing feature is definitely something worth paying for if you care about the environment.

            Comments appreciated.

            • Robin November 21, 2014, 11:06 am

              If you can fit a tankless, you can fit an actual boiler like HTP or Weil McClain. I did one of these “do it yourself” radiant systems, and I too went through three tankless units because of the heavy loads. I agree they are cheap to replace.

              Instead of detailing why they are bad for radiant floor heat, I will just say that I recently went through a heavy duty “I gotta be green” phase, wherein I cam into a bit of money and did stuff like buy a Nissan Leaf car, solar panels on the roof, etc. And I decided to switch out my tankless for an actual boiler with a crazy AFUE efficiency rating. It’s a $3,600 boiler with 98% efficiency.

              My heating bills went down by half. Like, $350 per month down to $100-150. Much less electric too. I know that I’m dumping a heck of a lot less global warming gremlins into the air.

              The floor feels 100% warmer, and my thermostat has been turned down significantly. Bottom like, a boiler should be used for the floor heat. Period. Tankless units are a bad idea, unless you have a cheap small cabin you need to heat part time or something. For a real house with real people and real space to heat, go with a boiler.

              Tankless units don’t modulate. They are racecourse that fire up to 199k btus overtime you turn it on. And the real efficiency of them is actually around 75 to 85%, not much better than granny’s old furnace. A boiler, on the other hand, can modulate the temps much better, which is what a boiler needs to do to continuously reheat the heat loop.

              Finally, I know of no locality with building codes in the nation that allows open systems. They are just a bad idea. Google open system and legionnaires disease.

              Other than that, I do agree, radiant is the way to go! Anybody who complains about the price of it maybe has never lived with radiant heat. Once you go radiant, you don’t go back. It’s like spending the extra money on a solid Mercedes or Toyota with heated leather seats that will last you 20 years, vs a Kia or Ford Pinto with no FM radio that will be junk in 5 years.

              Sorry. My fat opinion. ;-)

            • Mr. Money Mustache November 22, 2014, 4:58 pm

              Hey Robin, glad to hear you are enjoying the boiler. Just a couple of tech corrections, since I now have quite a few hours of run-time on my system:

              – tankless works great. It probably depends on which unit you get – mine is a higher end commercial Rheem that does indeed modulate and run efficiently, whether the flow rate and temperature rise is low or high. Taking before/after readings on the gas meter, I find the system can keep the house warm through a subfreezing night for under $1.00 in gas. (Then the sun usually takes over around 7AM in my region and heats the house through the solar wall).

              – Legionnaire’s is not a concern at all in this system. As it turns out, I keep the loop temps at 140 to get a nice heat transfer, so the water is never cool enough to allow the bacteria to form. On top of that, when you run the domestic hot water, you are pulling it out of the loops and drawing fresh water in. Not only will this prevent stagnant water in the off-season, it will actually provide water-based cooling to the entire floor system all summer, while pre-heating water before it hits the water heater!

              So far, it’s proving to be very effective and lots of fun too.

            • Chris January 19, 2015, 3:48 pm

              I have been installing these type of open loop systems for over 10 years, of clients as well as my personal homes. I have never had any issues with leaking. As most of you know radiant is best utilized in a concrete slab operation but can also be effective in staple up scenarios. I have had tremendous success with Takagi tankless heaters (with the exception of the earlier TK-1 models, although the did replace it for free.) Other than that they have been pretty bullet proof and they are very economical. I recently bought a new house and we will not be doing radiant rather utilizing mini-splits, as soon as I have time to install them. I did install a heat pump hot water heater (The $1,000 rebate from the electric company was just too tempting, considering the $1,200 cost) and I am really impressed its probably 10x more efficient that hot water coil coming from oil fired boiler. It serves as a dehumidifier in the basement and can even be ducted into living space to provide some cooling in the summer. Its peeked my curiosity if one of these units could be used in the same open loop or heat exchanger to run radiant. If anyone has feedback on this I would appreciate it.

            • Frans Slothouber December 7, 2020, 12:55 am

              Hi Robin,

              Question do you use a heat exchanger or have two separate heating devices?

              Thanks in advance for you response.
              With kind regards,


          • Christine October 10, 2017, 9:57 am

            I am a mother helping my son install radiant floor heat in the tiny house that he is building. I have it set up to match what you have done. We have 2 zones, and I am trying to figure out how to set-up the controls to operate the system. From the picture in your follow-up article, I see where you have the temperature sensing leads attached to the system; but I am unsure of how to connect actuators and thermostats for each zone. Any help that can given in this area would be GREAT! Am I correct in saying that I only need a 2 wire actuator for each zone and that a simple non-programmable thermostat for 1 heat pump would be sufficient? Thanks in advance.

        • David W February 18, 2014, 2:33 pm

          Perhaps so the pump is moving slightly cooler water? Temperature and MTBF are directly correlated. Just a speculation, there could be other factors I’m not thinking of.

        • ken February 3, 2015, 6:27 pm

          Best practise is to have the pump push to the load with an air elimination valve before the circulator.

      • David February 17, 2014, 12:31 pm

        Would love to help/see this installation. I’ve been thinking about doing the same thing for my house, but can’t afford it yet. I’d like to get the experience and see how it’s done though. Hit me up if you need help!

      • Kamil February 17, 2014, 3:25 pm

        Hi MMM, thanks for this article. We have radiant heat in our bathroom and kitchen which were recently remodeled. Both have tile/stone floors. Are there any other floor materials that work well with radiant heat? Our house is 100-years old and has wood floors throughout, so I am wondering if I would have to replace them with tiles or continue with wood or a similar product.

        • Sarah February 19, 2014, 10:19 am

          From my reading, tile is the best because of its effective heat transfer abilities. That said, my uncle installed a radiant floor heating system in his house and his floors are bamboo over slab. I am looking at the feasibility of retrofitting our next house (it has a crawl space) with radiant floor heating. I know that for a wood floor, the aluminum heat reflector plates are an important feature and I will need to insulate from underneath. Wood floors can also warp under certain circumstances.

          • ken February 3, 2015, 6:29 pm

            Tile and stone have more mass so they hold and radiate the heat longer

      • Paul March 19, 2014, 8:39 pm

        I enjoyed reading your plans, and especially like the SS adjustable plenum to fine tune zone. I have researched this at length and have a few items for you to consider.

        1. The heat exchanger in an on-demand hot water is designed to consume a few PSI, not a problem starting with 40 or 50 psi. However, your pump maxes out a head of 12 feet of water (5.2 psi) if you want 6 gpm. You may have a pump that is too small for the job. I cannot find a pressure drop curve for any on-demand heater, but suspect that at 6 gpm it may take 3-5 psi.

        If you have 2500 ft of half inch tubing, flow of 0.25 gpm/100 ft, you need 6 gpm. Example: 8 loops, 300 ft/loop, each 3/4 gpm.

        2. The problem of stagnant water in an open loop system (bacteria growth) is addressed by adding the cold water into the floor system, and then going through the heater, as shown here

        3. In addition to the circulation pump possibly being too small, running heated water back into a heat exchanger (as found in an on-demand heater) can lead to fouling, further constricting flow.

        The solution that looks best to me is included here:

        It uses a small storage tank (6 or 12 gallons). The tank is well insulated, consisting of a small electrical unit, heater disconnected, and the thermostat controls a second Taco pump. In addition, an auxiliary strainer is added to protect the on demand heater.

        4. Your floor heat may require an inlet temperature greater than 120 F. If so, a mixing value should be added to cool the heated tap water.

        Looking forward to project updates!

        • Mr. Money Mustache March 20, 2014, 8:35 am

          Awesome research Paul – thanks very much and I’ll incorporate it.

          (Building out the rest of the system has been delayed a bit because I’m focusing on electrical/insulation/drywall so we can move in, and we’ve reached the warm season in Colorado so heating won’t be required for another 7-8 months. Woohoo!)

    • cynthia February 18, 2014, 12:59 am

      Great Idea MMM–but one word of warning to readers!: we have this heating system in France, it’s very common here. BUT it works best in climates like yours in CO and Northern-ish climates, and is not at all recommended for more southerly climates because, as our architect friends here have explained to me: it takes a while to warm up and cool down, so if you live like say in Florida or Georgia or California, where you may have a few cold days then a few warm days, you can’t regulate the system quickly. Sure you can turn it on and off, but the radiant heat in the floor and pipes stays awhile. So it’s perfect if you have a real winter and need heating from say November to April/May.
      So our sister put this in their house on the Mediterranean (wrong climate for this!) and they have terrible problems getting their house the right temp, because some days its cold (5-10 C) then the next day it’s warmer with sun (15 C) and it doesnt work. They didnt listen to their architect who knew southerly climes better. By the way, for those climates they use here what they call ‘Canadian wells’ which are pipes that go fairly far under your house to where the ground temp is constant and thus keeps the house temp fairly constant.

      Another thing they do here: in the summer you can have those pipes circulate cool water for ‘air-conditioning.’

      So just a word to the wise from experience!

      • Zac February 27, 2014, 7:13 pm

        The cool thing about radiant systems is the many additions you can add to them. Add a small amount of ducting, an air to water heat ex-changer with a blower, a relay and a thermostat. and you can pull the heat out of those lines close to instantaneously. I did this addition with a portion of my house so I did not have to wait for the pipes to warm the house up. Kind of like hooking up a car radiator to your lines. It pumps the hot water through the radiator and a fan kicks on and pushes cold air through the heat ex-changer the cold air passes through the hot water and becomes warm and out into your home. The thermostat controls the fan.

      • Tania Moreno February 14, 2019, 1:09 am

        Hi! I will be moving to South Colorado. The idea of using it for AC/heat would be an excellent idea!! I know in Europe my family uses this since before I was born. Would they know how to do that here in the US? Thank you!-Tania

        • Joe the plumber February 24, 2019, 12:32 pm

          In the U.S. these systems go by the name of heat pumps, or geothermal systems (geothermal uses the ground’s constant temperature to regulate your house temps). Heat pumps work well to about 20-25 degrees Fahrenheit, below that you may need an auxiliary gas or electric heat system.

    • Jeff February 18, 2014, 11:42 am

      I’m disappointed you’d spend $500 for the aluminum reflectors. On Builditsolar website it shows you how to make them cheaply using aluminum flashing. They are easy and cheap. They have a lot of DIY solar collectors too that work very well out west.

      Unfortunately I live in the Great Lakes area where we have mostly overcast days in the winters or I would build a system. I did design and built myself my house with a lot of southern facing windows to get as much passive solar as I could. When building my house I did all but the concrete work and the drywall. I saved a ton of money and have a very well built house.

    • robert blake October 16, 2014, 6:54 am

      we want to use an airtight wood burning stove for our heat source and incorporate the in-slab radiant floor heating system. How can we accomplish this. Cost and being green are our two considerations in choosing this design/system. My thoughts are a closed system with non-toxic glycol to heat our place…………now I am considering the use ability to utilize hot water for household use. Please comments and ideas for our successful design.


      • Douglas Merkley December 9, 2015, 1:48 pm

        I have an outdoor wood boiler (Heatmor) to do this now. It heats a glycol/water line to my house, then the manifold splits the lines to the hot water tank, the furnace coil. Now I am adding infloor heating lines for the cool rooms.

  • Miss Growing Green February 16, 2014, 12:05 pm

    Wow, awesome post! We’re in the middle of a big remodel and writing DIY remodel blog posts too- it’s nice to see this one from you (*loved* your Pex one by the way). Couple questions, coming from someone who has never installed or owned a radiant floor system, so bear with me:

    * So you’re heating your house with a water heater/boiler instead of a traditional furnace… what’s the energy loss factor associated with each of these? I.e., is the water heater more efficient? It seems like you would have heat loss in the tubing much like you do in the ducts for a traditional furnace.

    *Do you need to insulate the tubing/pipe delivery system to prevent heat loss in the crawl space areas?

    Pretty awesome that you can get all the parts for around $1,100! The next time we do a whole-house remodel to the point where we have access to all the floors I’ll definitely be considering this!

    • EscapeVelocity2020 February 17, 2014, 11:04 pm

      I really wish you would go into the details on electric vs. natural gas. We had radiant heat in Norway. Granted, hydroelectric power generation certainly skews the equation in that part of the world, but it also makes installation and control incredibly easy. We rented an ancient house, and the floor heat was incredible. For all of the circuits that had burned out, there were still plenty that made lying on the floor our favorite winter past time :)

      • Mr. Money Mustache February 20, 2014, 8:27 pm

        Electric heat is indeed much easier to install. If our power weren’t generated by 50% coal in this country, it would be cleaner environmentally too. Actually, I buy 100% wind-credit power for my own place so it is theoretically clean.

        But electric heat is MUCH more expensive. 10 KWh of electricity costs about a dollar here and is good for 34,000 BTU of heat. The equivalent amount of heat via natural gas is 26 cents at today’s prices.

        So electric is four times more costly. If gas doubles and electric slices in half, then we’ll be talking. This could actually happen someday in the future, if our fracking supply runs out and solar electric continues to drop.

        • Douglas Merkley December 9, 2015, 1:52 pm

          It’s way cheaper to heat with wood (Heatmor), especially when I can get wood for free!

  • Micah February 16, 2014, 12:07 pm

    Fascinating. So are you doing away with all forced air? What are you doing for cooling?

    • mrs.m180 February 16, 2014, 2:17 pm

      Maybe the water temp can be lowered in the summer so you’d have constantly flowing cold water cooling the floor? If I know MMM though, his answer would be something like “take my shoes off and enjoy a cold beer, that’s how!”

    • Mary w February 16, 2014, 2:21 pm

      You must be a new reader if you think the MMM family is wimpy enough to require air conditioning!


      • William Murphey February 17, 2014, 7:58 am

        My sisters lives in Colorado Springs and she too needs no air conditioner. I’ve visited during the summer and we open the windows and/or turn on the ceiling fans.

    • MIke Avery February 17, 2014, 6:32 am

      When we were fortunate enough to live in Colorado, few houses had air conditioning. Ours didn’t. There were probably less than a dozen days where we felt any need for it.

      The locals at the higher altitudes complain when it gets above 80F, and have few occasions to do so.

      When we did need cooling, we found a portable evaporative cooler (i.e. “swamp cooler”) worked wonderfully because the air in Colorado had such low moisture content.

      All that said, this would be a very real consideration for people in less fortunate parts of the country. In the southwest, air conditioning is not a luxury, it is a necessity.

    • Jamesqf February 17, 2014, 12:17 pm

      In most of the mountain west, air conditioning is simply not needed if you have any sort of decent insulation. Even on the hottest days, the outdoor temperature drops to the low 60-50 degree range at night. You open the windows at sundown, the house cools off. In the morning, close them again, and it stays cool until late afternoon, at least.

  • Brendan Long February 16, 2014, 12:20 pm


    > And of course, everything is done in PEX, to eliminate the cost, slow installation, and heat loss of copper pipes.

    Isn’t heat “loss” the goal here, since you want heat the leave the pipes and go into your rooms?

    • lurker February 16, 2014, 5:12 pm

      good point but may be a typo!

    • Cid47 February 16, 2014, 6:53 pm

      I was thinking this exact same thing. Curious to see what the engineering/logic behind it is..

    • Shawn February 16, 2014, 11:32 pm

      I believe he means the heat loss in the runs, from heater to floor. The available area of heat transfer will easily get the heat loss into the floors with copper or PEX – but this will limit losses getting to the floors.

    • LL February 17, 2014, 3:04 am

      Sounds like some heat radiation (“loss”) is the goal for tubing under the floors, but I’d think that less heat loss means the heat dissipates in a more controlled manner. That, in turn, allows the variable speed circulator to pump water slower and the tankless water heater to be on less often.

      You definitely want the tubed routing in the boiler room to have the lowest heat loss at that stage before it goes under the floors.

    • Roch Naleway February 17, 2014, 12:04 pm

      Ok. There are two thing to consider: heat loss and heat transfer.

      MMM’s system has a low amount of heat loss, since it is using pex, which will efficiently transport the heat via the water that is pumped through the pex lines. Water is a much better conductor than air. Less heat is lost while being transported via water than air. The only liquid that is conventionally used and better than water: refrigerant. With that said the heat losses will be further reduced when the floor gets insulated. The insulation will minimize heat losses into the crawl space and maximize heat transfer into the living space.

      Instead the heat will be transferred via the metal plates to the floors in the living space. The more biomass in the floors the better the transfer.

    • sig February 17, 2014, 4:06 pm

      I wondered the same thing, Brendan. Since the goal is to transfer heat from the water through the conduit to the floor, which material is best suited? Without properly researching it, I assumed copper would actually be better for this than PEX. PEX seems like it would be a better insulator.

      It would be interesting to see a side-by-side comparison. Comparing with and without the aluminum reflectors would also be interesting.

    • jestjack February 17, 2014, 4:24 pm

      I’m thinking that’s what the $500 in reflector plates is for…to aid the release of the heat in the pex to the floor above. i’m wondering if if there will be insulation with the pex and if so what kind…

    • ken February 3, 2015, 6:40 pm

      You do heat loss calculations for your windows ,walls etc. then size your system to compensate for those losses

    • Jeff September 21, 2016, 11:40 pm

      Copper would lose the heat too quickly. Pex slows down the transfer which means a length of conduit can travel farther. This is why you have a manifold, to distribute the heat into branches. Also you would use less energy reheating the circulating water as it would stay warm longer.
      But in reality, the copper is heating the concrete. The buffer will eventually build up enough energy that there will be a returning warmth.

      My concern is the cost of heating water with gas. I could understand if you used gas as a back up when sunlight wasn’t available. There could also be a wood stove involved. But the guy really should incorporate some kind of free fuel source as well. Even if just to provide the room for expansion later, so it’s easy to tie in.

  • Eric February 16, 2014, 12:20 pm

    Great post. Have you considered integrating a solar water heat collector, or how you might retrofit one in? You could preheat the water going into the gas heater for further gas savings. What are your plans for home cooling?

    • Roch Naleway February 17, 2014, 11:48 am

      It is possible to integrate a solar thermal heater with this system. The system cost is pretty expensive though. MMM would save $250 per year. The material alone would cost $3,000-$5,000 and it would take up some space.

      The payback with the existing system is not that attractive with the efficient gas tankless hydronic system in place: 10-20 years.

      There are better ways to spend the incremental dollars.

      • Mr. Money Mustache February 17, 2014, 5:27 pm

        Yeah.. we’ll do a solar experiment later on, but it will probably be a simple one like a solar-heated outdoor shower. Solar electric will come in the future, especially if grid-tying becomes profitable in my area, or if I end up with an electric car someday.

        • JT February 26, 2014, 10:11 am

          With the amount of sun in colorado, a passive solar shower would be a cinch.

  • Jason Merrill February 16, 2014, 12:21 pm

    How does the transferring-heat-to-the-floor part work? It sounds like PEX is a decent thermal insulator (more so than copper), which is great for piping hot water around the house, but not so great for applying the heat in the places you want it. One of your pictures appears to show some copper plates attached to the underside of the floor with the tubing running underneath it, but I don’t see any description of how exactly that works.

  • shadow February 16, 2014, 12:22 pm

    If you haven’t already, check out Passive House design. It’s the way to go.

    • Corey February 16, 2014, 3:32 pm

      x2! I just took a Passive House training course and was blown away – totally the way we’ll all be building (hopefully) in 20-30 years.

      I was surprised actually that MMM has never mentioned it, given its “invest up front for insane savings later on” approach.

      • LennStar February 17, 2014, 3:32 am

        I hope we all start now – in germany (near) passiv standard is required for new (stand alone) houses since 2 years I think.

  • Andrew February 16, 2014, 12:29 pm

    I didn’t even know this was a thing and it sounds awesome! but i have a question.. you mention the PEX having the advantage of less heat loss compared to copper pipe. but in this case wouldn’t that be a good thing as it would heat your floors better? obviously PEX is better for a number of other reasons but ideally the more heat transfer to the floor the better, right? but I suppose the heat transfer plates will help offset this somewhat.

    • Joe February 16, 2014, 1:03 pm

      Regarding heat loss, you want enough heat loss that (as you mention) heat can escape the pipes and get into the floor. But you don’t want so much heat loss that all of the heat escapes before the water gets to the end of the circuit (causing uneven heating throughout the house). So there’s a balance.

      With a recirculating system, the heat that doesn’t escape into the floor is sent back to the floor again. So it’s not wasted.

    • Money Saving February 17, 2014, 6:43 am

      I had the same thought. PEX sounds good from an insulation standpoint, but it seems like the exact opposite of what you’d what from a heat transfer a thermal body standpoint (low thermal mass)… I’d be real interested to see how it works out.

      Also, the photo of the living room looks simply awesome! Much open space – I’d kill to one day have a living room like that :-)

  • John February 16, 2014, 12:31 pm

    Looks great…

    The one thing I see missing from your system is a method of descaling. I.e., a way to flush out your tankless water heater. You may want to consider adding a couple of valves to enable this yearly maintenance…

    • Roch Naleway February 17, 2014, 12:09 pm

      MMM has some valves installed. You are right: definitely always install a tankless heater with easy flush valves. Much easier annual service that is required to ensure a long lasting system.

    • Huskinator February 17, 2014, 2:53 pm

      The Front Range communities have access to LOW levels of calcium in the water–in fact most draw first-use water from the continental divide as primary, and secondary from sandy aquifers–I never saw scaling on any fixture when I lived in Colo Spgs, and Boulder has similar quality water. That’s ALMOST enough reason on its own to move there.

      Here in the mountains of southern NM, the exact opposite is true–industrial strength softeners are needed to get some control of scaling.

  • Mark February 16, 2014, 12:32 pm

    The described system is the preffered system here in the Netherlands for new homes or homes that are fixed up. Here we insulate the floor, poor in a first layer of concrete, put in the piping, cover with concrete. Voilà, a highly efficient heating system that saves serious money. We even make sure to insulate between the floor and the (outside) walls so that the floor does not directly connect to the walls to prevent energy leaking outside. Highly efficient and comfortable way of heating that is becoming the dominant way of heating here in NL.

    • Andrea February 16, 2014, 4:54 pm

      That sounds good but very difficult to work on. What if you have a leak?

      • Dirk February 17, 2014, 11:49 am

        You won’t have any leaks. The system is put under high pressure first to check for any leaks.

      • Roch Naleway February 17, 2014, 12:21 pm

        Pex is super durable. It is built to last 50 years. Very unlikely to break down. If it leaked you would find some wet insulation on the underfloor. Shut off the system. Drain the water. Install a new fitting or section of pex pipe: done. Pex is similar to Lego. If you can play with Lego you can work with pex.

        • Kenoryn February 18, 2014, 11:29 am

          I think the question was with regard to a system embedded in concrete, no the between-joists system described. The usual answer seems to be that the pipes used will last a lifetime. I guess they figure that after a lifetime, when they start to fail, someone is going to either tear down the house or tear up the concrete floor. Seems a shame. I guess for the most part most people figure it won’t happen in their lifetime anyway so they’re not concerned.

          • aitorbk March 9, 2014, 10:03 am

            The solution for that is using water -proof concrete.
            That way, even if the pipe corrodes in 50 years, the concrete will act as pipe.

            So he pipes should last more than 100 years.

            The problem is not completely solved… as the structure might move a little bit, and the pipes can’t really bend well as they are embedded. they will then get hairline cracks (and also the concrete). I had that problem less than one moth ago in my flat.

  • Jamesqf February 16, 2014, 12:39 pm

    Couple of questions. First, are you doing baseboard heaters, or underfloor heating (the updated version of the Roman hypocaust)? If the latter, what about insulation & access?

    • Roch Naleway February 17, 2014, 12:22 pm

      He is doing underfloor heating. Accessible via the crawl space.

  • Andrea February 16, 2014, 12:40 pm

    Wow. What a helpful post. I bet you could ebook this whole affair, charge 30 bucks a pop, and people would still thank you for the valuable hydronics info. I hope it works out!

  • Joanie February 16, 2014, 12:40 pm

    Just wondering if this could also be linked to geothermal energy? My parents heat and cool their home in Ontario for “peanuts” with a geothermal forced air system. (No more reliance on oil!)

    Wondering on the next renovation of their country home, if they could do radiant heating too? I have radiant heating in parts of my toronto townhouse – a sweater and warm floor is all we need, mostly (save this past crazy cold winter maybe!)

    I wish we had a government policy that all new homes have geothermal systems. Looking forward to more updates/photos on the house!

    • Garrett February 16, 2014, 3:24 pm

      All you’d have to do is heat a water tank using your geothermal system, then connect that water tank to your boiler’s inlet port. Then the boiler would only ever kick on if the geothermal wasn’t getting it hot enough.

      The cool “used” water from your house then dumps back into the water tank to be reheated before it starts the cycle again.

    • Jamesqf February 17, 2014, 12:24 pm

      “My parents heat and cool their home in Ontario for “peanuts” with a geothermal forced air system.”

      No, they don’t. What they’re using is a GROUND-SOURCE HEAT PUMP, which is a much different thing from a true geothermal system, which requires a hot spring or similar. They certainly aren’t bad systems, but the way the sellers manage to go on preying on customer ignorance is shameful.

      • RetiredAt63 February 22, 2014, 11:44 am

        That depends on how the system is set up. My last house was exactly that – a ground-source geothermal unit (closed loop, using coolant instead of water and transferring the heat/cool via a heat pump) that heated the hot water for the house, and heated/cooled the air that went through the air ducts. So it was geothermal and forced hot air/air-conditioning.

        • len February 3, 2015, 6:54 pm

          What did they use for backup heat?

  • josh February 16, 2014, 12:48 pm

    I’ve been thinking about doing something similar. You will attach the heat plates directly to the sub floor and twist the pex through the joists as shown? What is the thickness of your floor? Will you insulate from below?

    Am I correct in assuming this system operates at a fixed temperature set at the Rheem? Is this normal for residential boilers or do they do temperature modulation? What changes did you make to the design of the radiant loop to run at DHW temperature (120F?) ? Did you consider a mixing valve to enable different space heating/hot water temperatures?

    Presumably your renovation will increase the tightness of the envelope, will you have dedicated ventilation?

    • Roch Naleway February 17, 2014, 12:30 pm

      MMM has a Rheem tankless that can be adjusted to temperatures between 120-140 degrees. The model can be upgraded to run as a commercial heater with 150-180 degrees. A wall mount thermostat is also available.

      In really large system a second heater (or more) can be easily connected via an EZ-link cable. It coordinates the operation of two or more heaters. It offers a lot if flexibility due to the modularity.

      We recommend the installation of a continuous running Panasonic bathroom fan or Panasonic ERV for fresh air supply. Cannot tell yet how tight the MMM house will be when finished.

    • Becky February 18, 2014, 2:26 pm

      I am also curious about additional ventilation. My home currently uses this system, and in the 10.5 years we’ve lived here, we are fighting an ongoing battle with dust. While you don’t blow dust around with vents, you also have no opportunity to filter it out, either. We have no venting besides bathroom fans and the fan over the stove, and we have excess humidity and relatively stale air here in midwinter.

      We have a dedicated boiler, but it does use the drinking-water for the system, topped up as needed. As we live in Manitoba, the idea of having the house heat and “hot water” coming from the same source seems like it would never work, but in CO it’ll probably be fine.

      Love the blog! Being in Canada, I’d love to hear from Mr. Frugal Touque. I can’t seem to get my groceries (including paper/cleaning supplies) for 4 down below $1000/month, even buying in bulk and and making most things from scratch.

      • Douglas Merkley December 9, 2015, 1:57 pm

        I live in Canada (North Bay, Ontario), I have 5 kids a wife and a dog, and we don’t pay $1000/month for groceries.

  • William R. February 16, 2014, 12:51 pm

    Fantastic post. What I love about your blog is the fact that I not only come to read about resourceful financial advice, but I’m educated on other areas of life as well.

    I never heard about “Hydronic Radiant Heating” before and now the whole system fascinates me. As someone who constantly searches for alternative forms of energy to create a simple, energy efficient home, this is great information.

    Thank you and keep up the good work. I’m looking forward to the future posts detailing the installation process and results.

  • Joe February 16, 2014, 12:58 pm

    I’m planning out my basement remodel, and was researching this last week because of the space taken up by ducting in the basement. Now that we have insulation in the attic (the previous owners would upgraded the furnace but neglected to blow in $1000 of cellulose), it seems like we can get away with a lot less.

    Regarding insulation for this system, I’ll probably research moisture issues and put some XPS board in the joists. Maybe a half inch at a time, so I can play around with letting some heat into the basement area. Maybe I’ll try to rig some flexible metal tab system to hold the board in place, for easy removal if I need to get at the pipes.

    • Roch Naleway February 17, 2014, 12:34 pm

      Consider a ductless min-split heat pump if ductwork is takin up too much space. It is very efficient and easy to install.

      • Joe February 17, 2014, 6:31 pm

        Many thanks. I will look into that.

  • Mark February 16, 2014, 1:04 pm

    Oh, in diy stores here electric as well as water systems are sold for radiant heating purposes. The ones that use water are most energy efficient, the electric ones the easiest to install. Latest trend here is radiant wall heating.

  • Brandon February 16, 2014, 1:17 pm

    Where the cold water enters the system you show a pressure regulator valve. If you do not have one already, you will also need a backflow preventer to prevent pressurized water from your pump pushing water into the municipal water system.

  • Tristan Hume February 16, 2014, 1:20 pm

    One thing you might have to watch out for is how the variable speed pump deals with the “0.26 GPM minimum flow rate, 0.40 GPM minimum activation flow rate” of the water heater. If your pump tries to send water through your heating loops slower than that it will simply waste energy pumping around unheated water. This may or may not happen depending on how quickly your pipes radiate heat and how small 0.40 GPM is, I haven’t done the calculations.

    Another thing to double check would be how this kind of usage would affect the water heater. I was under the impression the tankless ones were designed for very bursty high flow usage, remaining inactive most of the time. It might be bad or inefficient at constant low flow heating. Depending on how robust it is constant low flow use may also shorten its lifespan.

    Disclaimer: I am a high school student, not a plumber, my concern is entirely based on intuition.

    • TMoney February 16, 2014, 2:40 pm

      That may be a good point regarding the use of the tankless water heater for this application but I will be interested to see how it all works out in the end.

      As far as the variable speed drive pump matching up with the water heater flows, most VFDs/VSDs allow parameter settings to give a min/max flow rate custom to the application (usually set in Hertz). So in this application you would set the minimum VFD Hz parameter to limit turndown to no less than the minimum flow of the water heater.

      I don’t know where your design for the house is at this point (I’m relatively new to the blog) but if the sidewalk/driveway is not done yet you may want to consider extending PEX through them as well…with possible valving/control combinations you can use it to provide free snow melting in the winter (we did something similar with a municipal hospital design that used steam boiler condensate that was normally being sent back to the utility- Just a thought!)

    • Grant Q February 17, 2014, 9:42 am

      I had the same thought about the tankless water heater running all the time; it will be interesting to see how this works out. I wonder if a higher-efficiency tanked or hybrid model like a GE Geospring would work better for this type of application?

      • Mr. Money Mustache February 17, 2014, 10:51 am

        It will probably run only an hour or two per day for heating – less than most houses use for showers and laundry. Will let you know actual stats once the experiment is up and running.

      • Kenoryn February 17, 2014, 4:11 pm

        A few years ago when I replaced my water heater, I was trying to find a condensing tank water heater – super high efficiency, actually higher than tankless, I believe, but also expensive (about $3000) and no one seemed to know they existed at the HVAC companies I was contacting! I gathered they’re primarily used for in-floor heating. I bet they would be awesome for this application, but a higher up-front expense. They also have the advantage of being able to heat water as fast as you use it, like a tankless, so you never run out of hot water.

  • Skidder February 16, 2014, 1:42 pm

    In the Netherlands (where I live), water-based heating is very common. As far as I know, they are all closed-circuit. I guess this is because the amount of calcium and oxygen is then limited to the quantity of water in the system, so descaling is not needed and the radiators (usually placed under the windows) do not rust internally. Also, the amount of air is limited so after venting the system it operates without bubbles.

    I have never seen such an open-circuit design, it looks efficient to use the same boiler for hot water and heating. However, at this moment I have a so-called ‘high yield’ boiler which combines an open (for tap water) and closed (for heating) system, they sell at 600 euros (800 USD). There even exist boilers with a Stirling engine, able to generate ~1kW of electricity while also heating your house, achieving very high energy efficiency. Note that the Netherlands is sitting on a natural gas bubble, so we use a lot of gas-based heaters.

    I guess the hot air heating has blocked innovation on water-based heating in the US.

    As an aside, when leading tubes through ‘non insulated space’, be sure to put proper insulation around the tubes (don’t want to loose that precious heat…)

    • Roch Naleway February 17, 2014, 12:40 pm

      Yes, circulating hot water is definitely tougher on the water heater than heating up cold water and not having it recirculated. It is important to maintain the water heater annually (flushing). If there are a lot of minerals in the water a water filtration/treatment system is needed: drip phosphate or water softener.

  • The Doug Log House February 16, 2014, 1:44 pm

    Here in New Zealand, these systems are becoming more common, but we generally bury the PEX within in the concrete slab that the house is often framed on. The slab is insulated underneath (and optionally on the perimeter) with polystyrene, and then a geothermal or air-source heat pump is often used to heat the water that gets pumped through the PEX pipes.
    Mr MMM couldn’t be more right about what a pleasant type of heating radiant heating is.
    I’ll be very interested to see another article on passive solar design.
    It can be quite daunting to work out a good design. “Thermal mass” is the other term to investigate in relation to a good passive solar design. The concrete slab we built our log house on is a good example of using thermal mass (along with the logs the house is built of) coupled with a good passive solar design to minimise heating costs even in a high Alpine environment. Orienting your house and windows to maximise the winter sun falling on an exposed concrete (or tiled) slab is a great way to heat your house. We supplement that passive solar heating with a large radiant wood burner for days when it’s not so sunny.
    I used Google Earth to work out sun angles in the high summer and mid-winter to work out how far into our house the winter sun would penetrate to provide passive solar heating.

    • CTY February 16, 2014, 7:40 pm

      We nearly did this heating in our old house–but we ended up relocating. That house would have been easily retro-fitted, because the pipes would be installed in what was essentially the basement ceiling. This set up would also allow for space to work/trouble shoot for repairs (which are inevitable). What I am having a hard time with is the concept of burying the pipes in concrete. It seems that concrete would greatly complicate any repair(s) needed later on–especially for the DIYer.

  • Bilgefisher February 16, 2014, 1:46 pm

    I would like to recommend a website that may peak your interest. Its called builditsolar.com They don’t sell anything and I’m not associated with them. He has some really cool step by step guides for solar hydronic heating in Montana that works quite well at 30 below zero. He built his system for 2k I believe using the side of his shed and a homemade 500 gallon water tank. He has also used it for cooling in the summertime. His website it to the DIY solar world what your website is to the financial world.


  • Max Power February 16, 2014, 2:18 pm

    Is there such a thing a radiant underfloor cooling? i.e. Could you run cold water through underfloor tubes to cool rooms in the summer?

    • TMoney February 16, 2014, 6:40 pm

      The closest I’ve seen to this is a technology called a chilled beam design, where a heat exchanger installed in the ceiling has chilled water flow through it to produce cooler air below. But this still relies on convective heat transfer (like forced air heating except the buoyant forces of cool air provide the air flow rather than a fan) and not radiant heating.

      • LL February 17, 2014, 3:33 am

        My school in Hawaii had this cooling system set up in its computer lab using cold deep ocean water running thru coils in the ceiling. Worked pretty well. It was never hot in there. Even if outside temperatures were consistently in the range of 78-90 degrees F.

        Their water fountains also employed a coil of cold deep ocean water for cooling the fresh water we drank.

    • Garrett February 16, 2014, 10:51 pm

      Theoretically, it seems like it would work but from what I’ve heard, if you try to run cold water through these systems, you can end up with condensation under your flooring which causes mold.

      • Tmoney February 17, 2014, 8:13 am

        This is true and is why critical environments like hospitals generally do not allow them to be installed

  • Kyle February 16, 2014, 2:46 pm

    Does the pump block the flow through the heat loop when it’s not running? If not, you might need to install a check valve so cold water doesn’t flow backwards through the system when you’re using the hot water when the heat isn’t running. Before the first freedom taco.

  • el-d February 16, 2014, 3:07 pm

    Can that Rheem unit run constantly? I thought that those were made to be on-demand water heaters. Just wondering if they’re built for the (relatively) high duty cycle you’re setting up.

    • Roch Naleway February 17, 2014, 12:44 pm

      Yes. This model can do it. They can easily be retrofitted for commercial use, too.

  • nathan williamson February 16, 2014, 4:03 pm

    Hey MMM, I’ve used that Amtrol tank and wouldn’t put it in an open system. Not designed for potable water, and you don’t need the hi temp rating anyway. They sell one for use with drinking water. Many states won’t allow open systems, make sure yours does.

    Love the blog dude! Keep up the great work.

    • Mr. Money Mustache February 17, 2014, 10:54 am

      Hmm.. I bought this tank specifically because it was rated for potable water (acting on advice of an amazing service rep at pex supply). Will double check and change article if needed.

  • tim February 16, 2014, 4:11 pm

    A number of the items on your list show pack quantities of 10 or 25 yet you list only (1) in the quantity that is priced out (escutcheon plates being one of these items) are you really getting 25 for $4.75 or do you only need one?

    Thanks cool project. We visited friends inDenmark and this is common there.

  • Alicia February 16, 2014, 4:54 pm

    I don’t have any advise, but wanted to tell you that you’re house looks awesome!! Way to go. Can’t wait to see it when it’s done.

  • Nick February 16, 2014, 5:09 pm

    Hmm, I guess I am missing something. How come it has to be a tankless hot water heater? Wouldn’t a regular hot water heater on a closed loop bring all water to whatever the set temp on the water heater was and maintain it? I guess there might be a duty cycle I am not thinking about, but I don’t understand why an element that is submerged would have a duty cycle. Standard water heaters are super cheap. You would be limited to whatever wattage (5000?) the water heater puts out. Isn’t that about 20000 btu?

    • Mr. Money Mustache February 17, 2014, 8:49 am

      Yes, a tank heater would work too – just less efficient than tankless, and takes up more space. With tankless, I was able to squeeze the whole thing into the crawlspace, freeing up more interior space.

  • Andrew Alexander February 16, 2014, 6:13 pm

    Mr. MM, will you please be sure to write an article detailing your amazing ceiling destruction and re-struction? I mean, I’m sure it’s on your list, but seeing at least a partial picture of the roof makes me so curious!

    • Mr. Money Mustache February 17, 2014, 8:48 am

      Oh man, that was a war zone, taking off the old roof. Over 10,000 pounds of plywood-and-shingle sandwiches and old trusses, manually cut off with a circular saw and heaved into a dumpster. Then all the drywall and powdery insulation showering down inside. I will try to sneak some pictures into this blog in the future, or make a dedicated page just for true DIY-heads.

      Framing the new roof, on the other hand, was easy and pleasant. Building new is much easier than fussing with old.

  • Lucas February 16, 2014, 6:27 pm

    Very cool. Thanks for taking the time to share, and to the leg work on distilling a project like this into something that many of us can attempt! I have another part of my dream home mapped out now ;-)

  • Liam G February 16, 2014, 6:53 pm

    I design a lot of these systems. What MMM is proposing will work. There are some advantages to spending a little more money, but not much more money.

    The issue of descaling is mentioned above. Installing a few boiler drains to descale the unit would be quite helpful.

    Depending on your local water’s hardness, you may opt for a water softener, OR to use a separate heat exchanger for the domestic water, rather than run the domestic water through the boiler. We have incredibly hard water where I live (State College, PA) and I have seen boilers fall apart within 2-3 years when running potable water constantly through them. With the addition of a pump, a head exchanger, a little pipe, two boiler drains and two ball valves, you would have a separate domestic water heating system that you can descale when necessary.

    I would recommend pressure testing the system prior to filling it with water. It’s much easier to fix a leak when air is in the system, than water.

    We have installed these systems in basement slabs, so there is no future access. You have to take some precautions (PVC Sleeves where you have expansion joints, air test for 24 hours prior to pouring cement, etc). Other than that, just don’t put a nail/screw into the pipe once the cement is poured.

  • Rural February 16, 2014, 7:01 pm

    I’m fascinated to see how this goes. We looked at radiant heat for our (earth-sheltered, on slab) house, but, given that the biggest challenge in underground houses is moisture, and since there’s no working on any potential leaks in radiant heat systems in a poured slab without a jackhammer, we decided we just aren’t that brave. If we’d had a crawl space, definitely. As it is, our heat is passive solar augmented with window unit heat pumps, but my feet would have loved for all this concrete to be warm! It’s insulated, so it’s never cold, but it isn’t warn, either.

    Good luck!

  • Kirsty February 16, 2014, 7:04 pm

    Underfloor heating is used a lot in northern Europe as it’s considered the most efficient way to heat a house. Water is a lot more cost effective than electric underflloor heating.
    I have underfloor (electric) heating in my kitchen/dining room/sitting room – it was already installed when I bought the house – and there are three thermostats for the three different zones.
    One thing I have to say it’s more hygienic (no dust blowing about), Also the floor is tiled and the tiles hold the heat long after the heating has been turned off. I also find its a lot warmer than the traditional central heating system we use in the UK.
    I’ve not heard of anything going wrong with the water underfloor heating and so far my electric underfloor heating has been fine but apparently if anything does go wrong with it there are companies who can come out and locate the fault to the exact spot so any repair work is minimal.

  • CTY February 16, 2014, 7:46 pm

    BTW thanks for the discount codes and bartering on our behalf–I won’t be needing them–just thought it was very savvy.

  • Ed February 16, 2014, 7:47 pm

    Mr. MM. Glad to see you doing this. Growing up my Dad GC’s his own house I I did a lot of misc work for him when he did it. We put in about 8000 sqft of radiant heating. 15years later… very comfortable although if everyone is comming on a cold day and a bunch of cold air comes in it takes a while for that air to warm up. Leak prone…had many issues with leaks over the years. Make sure each room has two home runs back to the manifold. If one leaks you can abandon it and keep using the other. Also we abandoned a pressureized system and put the water/antifreeze in a resivior in the attic to create just a minimal amount of head pressure on the inlet side of the pump. Put the thermostat in a non drafty non sunny place. It takes hours for the warmth in the tubing to heat soak the house.. the thermostat can overshoot and then you will be in a hot box..if you get this right one zone will be fine. Make sure you have some valves for each room or get a manifold with valves on it…its a must to balance the different areas of the house.

    Save room for one of these for when you get tired of spending $ on gas: http://www.miamihp.com/store/HPHWW%20Series.html


  • Kevin Leclair February 16, 2014, 8:03 pm

    I’ve been reading this blog for quite some time, this article is close to home I also build a DIY radiant hot water floor, it’s awesome. The cost of the heat transfer plates were cost prohibitive. I ended up getting a roll of aluminum from the HD and making a jig out of some plywood and an old hinge and a rounded dowel. and I pressed all the heat transfer plates with a sledge hammer. saving a bundle.

    • Mr. Money Mustache February 17, 2014, 8:44 am

      NICE!! I was wondering about that, after my $500 of aluminum plates arrived and they were only two 4ft boxes, weighing a total of maybe 50 pounds. The spot price of aluminum is about 80 cents a pound, so I’m pretty sure someone is making a bit too much profit.

      • Maverick February 18, 2014, 12:35 am

        Been there, done that. MMM, the AL plates you purchased should be, I assume, annealed AL such that you can easily conform to the PEX tube diameter. That’s why the cost is so high. AL trim roll as suggested by Kevin is far cheaper…but is NOT annealed, so it springs back when trying to form it and may make noise during expansion/contraction. In the end, you likely won’t need the aluminum emission plates anyway. Given enough time, the PEX will radiate the heat to the surrounding building materials of your home. I have built my own radiant heating system from commercially available parts and the human comfort is unmatched by any other heating system I know of.

  • Doctor Vacation February 16, 2014, 9:54 pm

    Here’s another way to get heated floors (and walls) – live in a condo in a modestly-priced building (as long as it’s not a top floor or end unit); your neighbors on all sides will help keep your place toasty warm! Spoken from experience in Avon, Colorado, at the base of Beaver Creek Resort.

    And MMM – if you and the family want to come to the Beav for a day of skiing, we have coupons for $50 lift tickets that have your name on them!

    • LennStar February 17, 2014, 3:47 am

      Especially if the people around you are heat-loving old people. I rarely have to switch on the heating if its above the freezing point.

      • Gerard February 17, 2014, 6:45 am

        Or if all your neighbours have immigrated from a hot country! My condo building in Toronto is mostly people from Bangladesh, and I rarely have to turn on my heat in the winter. I also have (electric) radiant in-floor heating there, and I absolutely love it. I find I can keep the thermostat turned down way lower than in my forced-air-heated house.
        Which brings up a different issue… I get the science-experiment motivation, MMM, but even in your not-fully-optimized current house you use very little heat. Would it make more sense for most people in your situation, with the new super-optimal house, to go for a cheap-to-install but maybe expensive-to-run system, given that you’ll so rarely need it?

        • Mr. Money Mustache February 20, 2014, 8:18 pm

          Yes Gerard! That would totally make sense.. if I didn’t have this blog that motivates me to do these science experiments.

          This way, others can either laugh and learn from my failures successes, I get to promote the idea of a better heating system than forced air, and I learn more things too.

  • JayP February 16, 2014, 10:02 pm

    Eventually everything old becomes new again. Boiler systems with radiators were in every home in the 20’s and 30’s. They’re wonderful. The forced air systems dry out the air, causing your skin and eyes to dry out. I have seen boilers 60 years old work with no problems. I think the radiators were eliminated because of the high cost of them – they’re iron and weigh a ton.

    • John February 17, 2014, 11:50 am

      I was wondering if a radiator or two could be included in a system like this. Seems like a much more effective way to get thermal mass than aluminum plates.

      Perhaps you could find and old radiator at a salvage building materials site or through craigslist…

      • Conrad November 19, 2014, 1:01 pm

        I just bought a house built in the 1920’s with radiant heat run off an oil boiler. Any reason I couldn’t retrofit such a system to run in the manner MMM is talking about? I would love to get rid of my oil tank, my boiler and the costs associated with maintaining them every year.

        • AMJ November 19, 2014, 1:23 pm

          I’m creating a thread over on the forum. It is too hard to keep track of the where the comments are in this big mixed comments section.

  • Garrett February 16, 2014, 11:00 pm

    Have you considered which thermostats you’ll be using? We had hydronic baseboard heat in our old apartment, which is similar but with a baseboard radiator instead of the under floor tubing.
    These systems can take quite a while (several hours) to heat up the house but we were fortunate that we had a thermostat that attempted to be smart about when it turned on the heat.
    Basically, you just set the time that you want the house to be warm, and the system figures out how far in advance it needs to turn on the heat to bring the house to that temperature.
    It worked pretty well, if the outside temperature was relatively consistent from day to day. Of course, it also helped that we had regular schedules.

  • wordygirl February 17, 2014, 12:04 am

    I read up a lot on passive solar heating as well as radiant in-floor heating when we were researching building a house. One thing I haven’t seen you mention along with your lovely south-facing windows is the notion of thermal mass.

    You can capture all that sun coming in during the day and have it radiate out at night, just like the brick walls you talked about in a previous post remain noticeably warm even after the sun goes down. If you haven’t already, consider placing some thermal mass to help reduce your heating costs even further.

    Cooling is helped by having roof overhangs that block the high sun in summer, but let it in during the sunny days of winter when it hangs lower in the sky. There are online calculators to help you determine what that overhang looks like depending on your location on the planet.

    I’m looking forward to reading more about your project!

    • Mr. Money Mustache February 17, 2014, 8:09 am

      Hi Wordygirl, I am definitely a big fan of thermal mass. The new house has quite a few tons of it in the masonry fireplace and some other features (and I’m adding more): http://www.mrmoneymustache.com/2011/09/01/what-is-thermal-mass-and-how-can-it-make-you-money/

      • Tyler February 18, 2014, 5:10 am

        I’d love to hear more about this masonry heater. Were you able to DIY any of that? I hear they’re a bear to try and make, unless you go the RMH route — and that does not look like a rocket stove to me.

      • crazyworld February 18, 2014, 6:39 am

        I need to understand this a bit more. We moved into a brick home(built 1929) last year, and the internet kept telling me the brick will hold heat and keep warm, but the reality is it is always freezing here and our utility bills are double what they were in our previous (newer built) home. It is always uncomfortable in winter in here. Makes no sense. Oh, and it is quite hot in summer, but we deal with heat better, so that is fine. Bottom line, it is hot in summer and cold in winter.

      • 5inatrailer February 19, 2014, 6:16 am

        Hey Dude, love the blog. I don’t have time to read 218 posts so I’ll try and get your attention here.

        We are planning a similar system to our house build this summer.
        The “open system” has been banned from the building code here in alberta. My friend designed his exactly like yours and it seems ok. He used an inline backup heater also (stacked them)

        make sure you include timers to cycle the water- legionairres disease builds in standing warm water.

        What are you doing for air exchange? Passive – I doubt it, you’re going to make that sucker air tight. An air exchanger-> still need ducting.
        Just run a super efficient fan on all the time -> panasonic
        Where is the new air coming from?
        Do you need a humidifier?

        There are things we had to consider and in the end went with a high eff. boiler “combi” unit that heated water and had a heat exchanger coil on it to warm the air in the home.

        ok ttyl. off to work.

  • Mariah February 17, 2014, 12:05 am

    I read up a lot on passive solar heating as well as radiant in-floor heating when we were researching building a house. One thing I haven’t seen you mention along with your lovely south-facing windows is the notion of thermal mass.

    You can capture all that sun coming in during the day and have it radiate out at night, just like the brick walls you talked about in a previous post remain noticeably warm even after the sun goes down. If you haven’t already, consider placing some thermal mass to help reduce your heating costs even further.

    Cooling is helped by having roof overhangs that block the high sun in summer, but let it in during the sunny days of winter when it hangs lower in the sky. There are online calculators to help you determine what that overhang looks like depending on your location on the planet.

    I’m looking forward to reading more about your project!

  • Anonymous February 17, 2014, 12:31 am

    Very impressive work! Two questions come to mind:

    First, how realistic would it be to install a system like this into an existing house? Is it even possible without a massive retrofit?

    And second, if you’re in a climate where air conditioning is actually required and not optional, does this kind of system still make sense? What mechanism would you use for cooling, or does this system only make sense if you have no plans for cooling at all?

    • Roch Naleway February 17, 2014, 12:53 pm

      If you have access to the floor joists and underfloor it is doable to install it. You can get a ductless air conditioning unit to cool the space in the summer.

  • Mustanaamio February 17, 2014, 1:26 am

    How do you prevent that temperature in the loop doesnt go under 65 celsius degrees and that Legionella won´t start to grow in the loop?

    I suggest that you make basic heat exchanger build. So get those loop separate to make sure that no one gets sick.


    • Chris February 21, 2014, 9:01 am

      Good advice.

  • Tom February 17, 2014, 2:33 am

    a new remarks:

    1.) maybe you should to use a closed water circuit for the heating nd ideally fill it with purified water. having freshwater heated up and then use it for food is not a good idea.

    2.) depending on the location it maybe would make sense to look into such a solar heater (free energy from the sun) like this http://www.instructables.com/id/Solar-panel-air-heater-made-of-pop-cans/

  • Richard February 17, 2014, 3:43 am

    I installed UFH into my house here in England about 12 years ago.

    The ground floor has a concrete subfloor, 100mm polyurethane insulation 12mm pex pipes at 150mm spacing then a further 70mm of concrete on top. Each room has its own zone which is controlled via an individual room thermostat and zone valve on the manifold. I run the water at 35 degrees C and 2 litres a minute.

    The 1st floor which is suspended timber has the same pex pipe laced between the joists. These are fixed to aluminium spreader plates and have the same 100mm polyurethane insulation below them. I run the water at the same flow rate but a slightly warmer 40 degrees C. Again each room has its own zone.

    Because I am running the floors with low temperature water I use my boiler to heat a 200litre buffer tank to 55-60 degrees C (insulated with 200mm polyurethane insulation) which then supplies the ground floor and 1st floor manifolds. Each of the manifolds have a thermostatic valve which lowers the temperature to the desired temperature. The buffer tank enables the boiler to cycle for a reasonable time then switch off for around an hour before beginning the process again. To heat my house (and hot water) which is 1800 square feet costs £450 per year. That is using an oil boiler at 65p a litre for oil ($4.11 US gallon).

    I would definitely recommend zoning your system so that you are only heating the rooms that need it and to the individual temperature you want. The buffer tank (as long as it is super insulated) also provides a significant saving with the added advantage of been easily adapted to take solar, heat pumps etc.

  • Fiona February 17, 2014, 4:19 am

    We had sub-floor Hydronic Heating in our rented apartment in Sydney. All I can say is that it was like living in a high-end hotel all winter. Absolutely divine! To get out of bed on a cold winter’s morning and step onto warm bathroom floor tiles is a kind of luxury that never gets old!

    Our only problem was that the system in our rented place was electric. What a disaster for running costs. It was criminally expensive to run (our kWh rate for electricity here is – I think – about double yours in the US.) I see your boiler is (of course) natural gas so…enjoy those toasty floors to come!

    • Mr. Money Mustache February 17, 2014, 8:05 am

      Thanks Fiona,

      In Sydney’s climate, where it is warm year-round and the all-time-record low is not even freezing, I’d probably keep an extra pair of wool socks around as my only winter heat source :-)

  • Emilee February 17, 2014, 5:25 am

    I’m wondering if your hardwood floors are quartersawn? I’ve done research into retrofitting radiant floor heat in my house and have read that unless your wood floors are quartersawn (which is inherently more stable and less prone to warping), the radiant heat will destroy wood floors (read so much shrinkage and warping!), which is what has made me shy away from doing this.

    • Kenoryn February 18, 2014, 11:49 am

      Good thought. We are preparing to saw the floors for our future house and I guess we should look into this first!

  • Dburt February 17, 2014, 6:08 am

    I would recommend switching the pex over to an oxygen barrier type. That way if you ever decide to use a dedicated boiler the system will be ready and you or a future owner won’t end up with a nasty rusty surprise! I have baseboard hot water heat and it beats forced air anytime! I would personally make it closed loop and keep the potable water out of my heating system.

    One more thing, if you are going to use a Taco circ and changed to a closed loop solution, I would look at the bumblebee. It costs a hundred bucks less and uses less power to do the same thing as the pump you selected. Take a look, it is the way to go with a Taco for closed loop. I don’t know why Taco hasn’t released a stainless version. Grundfos might build an alpha in stainless…

    • michelle May 2, 2019, 9:40 am

      My ex and I replaced the baseboards in living room, dining room and kitchen with in floor radiant heat… well, we ran the pex (oxygen barrier) tubing and hooked it up to the boiler the same way the original zones had been attached (STUPID). This is stressing the boiler and it will no longer run this zone. I am very interested in hiring out the fix to this as I am from California and it gets cold here in Colorado, however I’m not sure where to look. Would a standard heating company take on the installation of another pump to the system? Is that even the right solution? I found some down pants at a thrift store but I don’t want to have to wear them all the time. Any help is appreciated!.
      – Michelle

  • Trianom February 17, 2014, 6:10 am

    I really like your DIY approach and admire the drive to find the best solution for your Home!
    Here in Germany these systems ar more or less the standard. Beeing an engineer i installed some of those systems myself (although permits and other regulation are on totally different level). Some remarks and potential improvements:

    1) i would put in a second measuring point (maybe even an thermostat) in the way of the cool water back to the water heater. If this temperature is to high your flow is probably to fast. At least it gives you more insight to improve your system.

    2) at the highest point of every loop put a small valve in that you can let air out of the loop – otherwise effincy might suffer

    3) keep the water inflow flexible enought that you later on either can integrate a solar heater or a wood burning device with intergrated water heater in

    4) In your actual design the need for hot water is trigered by the heatig system – i do not see how the shower or other devices would start the water heater – probably an oversight by me

    5) underfloor heating sometimes creates trouble with some Floors. Sometimes it dries out hardwood or the hardwood is to good of an insulation to have effective heating

    Greetings from Germany Trianom


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