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?


  • Jon B March 3, 2014, 8:58 pm

    You could also run baseboard heaters for some rooms in the house. They will save you money over running PEX in floor. PexSupply.com sell some nice covers for baseboard: http://www.pexsupply.com/Baseboarders

  • Filmotaku March 4, 2014, 3:20 pm

    Hey MMM,

    I’m not sure if someone else has brought this up or not but what about McMansions. A lot of people are complaining that your open system is a giant death trap for bacteria and other dangers to lurk. But what about the McMansions out there. I’m pretty sure that these 15 bedroom 10.5 bath monstrosities have a shit ton of piping running through the house. How is your radiant floor system any different from all the pipe running through a McMansion. Seems to me that your system will be comparable with the added benefit of heating your house at the same time.

    • Mr. Money Mustache March 5, 2014, 5:00 pm

      Yeah, I don’t mean to minimize the seriousness of Legionella bacteria, but there is a reason it is a rare disease: it is rare for the bacteria to multiply to dangerous levels.

      When I think about all the second houses in Florida that sit unused for half of every year, the millions of water heaters that are in the temperature range where that stuff grows, the old tall apartment buildings with their own unregulated water tanks, and then look at the stats for the disease – even if you multiply them by 10 to account for any under-reporting.. it is just not a significant danger compared to, say, sitting on your ass watching TV for an hour a day.

      However, I will still set up my own system so the water can never stagnate in those pipes. They will be constantly refreshed with fresh chlorinated city water.

  • The Idiot March 16, 2014, 7:41 am

    I was reading about these the other day in a local Australian forum and needless to say it was all about who was installing them etc. I’m constantly struck with how much you’re allowed to do in the US. I swear in Australia it won’t be long and you’ll need a ticket to change a lightbulb and washer. You can’t do anything electrical and plumbing, pretty much no additions. Gas – forget it.

  • Mark March 20, 2014, 10:46 pm

    I’d worry about temperature swings in your shower whenever the pump starts/stops.

    Separate zone pumps would be preferable to valves, and a tank-style water heater wouldn’t hurt your efficiency much. The tankless style can be a real PITA if you have hard water.

    All those twists and turns could also cause a problem with the water off-gassing in the heating loops, leading to air bubbles coming out while you’re in the shower. An air trap with a bleeder valve installed downstream from the heater would help to prevent some of those issues.

  • Mike Beaver March 29, 2014, 1:04 pm

    I built a house in the Bay Area (CA) a few years ago and agreed with the architect to go radiant heat. Starting from dirt, left a lot of choices. The first was to use a sub floor system designed for radiant heat (Warm Board). This is just 1-1/8″ plywood with channels routed for PEX and a layer of aluminum formed on top. This puts the tubing on top the sub floor for lower thermal resistance and the aluminum spreads out the heat. It has performed well. I started with a tankless water heater, but after a couple of years, switched to a high efficiency conventional heater. Both were rated for domestic hot water and radiant heating. If your building inspector is on the ball, this will be required. The reason for the switch was that my wife demanded an end to the “cold water sandwiches”, where the water heater turns off when the flow drops below the minimum. This is inconvenient when washing dishes (and encourages wasting water), and not nice in the shower.
    My system has 8 zones, and about 12 loops of approximately equal length. I built my own manifolds, but would have preferred pre-built. Cost and availability were issues at the time. I have a plate-type heat exchanger to separate the radiant and domestic water systems, and this works well. It requires an additional pump, but I don’t have to worry about bacteria. I’m a bit surprised that your building department allows a combined system. With a separated system, you can add propylene glycol to the radiant section to control bacteria and corrosion. You also need another expansion tank, and a pressure gauge is nice. Using a variable speed pump on the input side of the heat exchanger allows you to get a consistent input temperature.
    On your system, it looks like you need a tempering valve on the domestic water outlet, especially if your heater is set above 120 degrees.
    The system performs well, but this type of system responds slowly. Mine will heat the house at about 1 degree per hour.
    When I was doing my DHW plumbing, I installed return lines so I could do recirculating hot water. I put a flow sensor before the input to the water heater and built some simple electronics to control the recirculation pump. The result is an on-demand system with no wiring except in the utility area. We just turn on the hot water for 1 second to start the pump. It runs for 45 seconds at high speed, then drops to low speed until 10 minutes after demand stops. I waste much less water and have hot water fast.
    I have a second system in my workshop, where I have tubing in the slab. It is now warm enough that I have opened two windows. This system is 100% solar heated, using the slab itself for heat storage. It only has one pump and 1 temperature sensor. I’m going to have to drain it for the season fairly soon.

    • Three Wolf Moon May 4, 2014, 11:27 am

      We had the “cold water sandwiches” after moving into our first house with a tankless gas hot water heater also. I told a plumber friend of mine about it who has the same unit and he said exactly the same thing, the flow rate was below the minimum to turn on the unit – but he added the reason was the previous owners had the temp control set to 140 deg F and when we showered we had to mix this with so much cold water to be bearable that the flow in the hot lines dropped to much. He said the easiest (and most efficient) solution was to set your temp on the unit to put out water at the temperature you like to shower at – for us that turned out to be 110. Now, we shower with only the hot water valve open – and we only use the gas to heat the water we are using, not to 30 degrees higher.

      The only drawback he mentioned is some people like to have hotter water going to their washing machine and dishwasher. Since we find “warm” water perfectly fine for clothes washing, the first one was not a problem. Luckily when I checked the specs on the Bosch dishwasher our house came with, I found that it comes with a heating element included that will boost the water temp to the desired level if the incoming water isn’t hot enough. Granted it uses a less-efficient electric resistance element to do that, but given how little we use our dishwasher compared to our showers it seems to be a better solution overall.

  • MikeG April 4, 2014, 11:38 am

    I found this PDF that others might find useful as well:


    It’s the most comprehensive guide I’ve found to explaining the science behind radiant heating, as well as covering about every type of application and construction style out there.

    I’m trying to install a radiant system over an existing concrete slab. The issue I have is keeping the floor as “thin” as possible but also filling the space around the tubing with some good thermal mass. I have read about sand being used (awesome for cost and simplicity) but apparently it also has insulating properties because it holds air between the particles.
    If anyone knows of another good alternative or something to be used in conjunction with sand (some sort of mixture) please throw it out there. I would like to avoid pouring concrete and I have read that a 1 1/2 inch slab is not a good idea (this is how much space I am trying to fill).

    MMM, I’m excited to see how this all turns out. This type of system is something I’ve been interested in for awhile and this post gave me hope for it! Keep it coming as I am planning on using whatever “mad-scientist” design you create as the blueprint for my system!


  • Ed April 9, 2014, 7:25 pm

    I’ve had radiant heat for several years and it does not excite me. Go away for a week or two and turn your floor off……and it takes a long time to heat the home up. My house heats at roughly 2 degrees per hour. So, you don’t want to turn it down too much in the a.m. and go to work, as it takes so long to warm the house up…I do like the nice simple design of mmm….Also, I find it expensive to run. I have a hot water heater with a heat exchanger in it, as I have a small house and a boiler is not neccessarily made for a small foot print. I have a radiant slab btw…. Poor mans way of coloring the slab is with a 5 lb. box of iron sulfate for $5. put it in a bucket of water and mop. Way cheaper and inviromentaly friendlier than acids….and it looks great :) My next home will have a ductless heat pump….GO MMM! Great site you have here!

  • Matt June 26, 2014, 9:20 am

    MMM, are you installing the PEX in a slab? I’m curious if you are planning on pouring a new slab to install this system.

    My wife and I were considering purchasing a mid-century modern ranch on a slab recently. The owner told me that his baseboard hot water heat had two leaks in the slab that needed to be repaired. (Numerous leaks in the slab have recently been repaired according to him.).

    If I were to purchase the home I was considering converting to a radiant hot water heat system, but that would most likely require re-pouring a slab.


  • Monkey of Austria August 1, 2014, 5:07 am

    Here in cold Austria, radiant heating is by far the most common method. I was surprised to learn that Americans are used to fan around hot air in winters. Although we always have one cycle for drinking water and a separate one for heating.

  • Joe Kato August 11, 2014, 7:42 am

    Hey MMM, Any update on installation progress of your heating system? Anxious to hear if it worked out OK?

    • Mr. Money Mustache August 14, 2014, 10:31 am

      Coming soon! The tankless water heater works great but the actual pump/pipes for heating are still partially assembled, waiting in the crawslspace as I’ve been away all summer. I guarantee it will be working before the Colorado heat season begins ;-)

      But so far, everything has been extremely easy to work with.

      • AMJ November 10, 2014, 9:31 am

        Still hoping to see how your system worked out for you. Your post inspired me.

        We bought our house in April and it came with a big Oil burning boiler for baseboard radiant and a rusting out electric water heater. With Natural Gas in the street that all had to go. I just finished the install of a Natural gas boiler and indirect tank. While it isn’t the Money Radiant system it was a stepping off point for me to learn how all of this stuff worked.

        Now I can solder or run black pipe no problem. Maybe I should be a plumber.

        • Mr. Money Mustache November 10, 2014, 1:53 pm

          Cool to hear, AMJ!

          I just added a footnote at the bottom of the article to say this system is working and I love it. I still owe everyone a follow-up article with more install details and lessons learned. As I type, Colorado is experiencing the first really cold weather of the season (in the 20s F and dropping), so it will be good to get some real testing in this week.

  • Donald November 2, 2014, 7:12 pm

    How has this system turned out? I’d love to hear how the system is working now that the temperatures have started to drop. I’m thinking about doing a smaller scale system in my house, but would love to go all out to be more efficient.

  • Jen November 11, 2014, 5:16 pm

    Hi- we too have radiant heat, although we have a geo thermal system (closed loop, buried in the bottom of our 1 acre pond)… anyway, just wondering how your utility bills have changed since using this system? (Hopefully you will include that in your update)
    Thanks for the great posts :-)

    • Mr. Money Mustache November 11, 2014, 5:37 pm

      It will take me a few months to get the utility bills reliably estimated. But even so it won’t be all that useful for comparison purposes: my house gets much of its heat from the sun and the woodstove. The radiant system is third on the list, which means there shouldn’t be much natural gas being burned.

  • Frank November 12, 2014, 6:54 am

    I’m in the middle of a full remodel of a cottage on a pond in Maine. It will be our home and will need to install a heating system. I’ve came across this thread and have been reading it and am hoping that your system works well because it makes great sense to me. I am doing almost all my work myself but am limiting my physical hard work to take car of my aging body… Not much digging, roofing, that sort of thing, but the rest is all me. Is there an updated list of materials and an updated drawing of the system? Our cottage is 600 sq ft and we are opening up a 200 sq ft of loft. Our full basement has a dirt floor that we need to pour a floor to remediate radon and may put pex in the floor. So we are primed and ready to go radiant and I want to do the install. Please advise ASAP, and thanks all for a great dialog! Frank @ Blueberry Cottage on Pettingill Pond

    • AMJ November 12, 2014, 10:32 am

      MMM’s crude drawing of his system was a great jumping off point for my redesign of my hydronic system. Something that I found very useful was using flow chart software to map out my whole system. It allows for a more flexible way to diagram all of the different interactions and adjust them for your specific situation. I used Lucid Charts 15 day free trial for all of my mapping of the system.

      If you are starting from scratch your first thing you should do is a heat loss calculation so that you can figure out how much work you actually need to do.

      Good luck.

  • Andres November 26, 2014, 1:32 am

    I just ripped the old carpet out of my basement, and want to add underfloor heating (along with insulation and properly sealing it against moisture). I’ve got the sealing down (courtesy of buildingscience.com), but I’ve been on the fence about hydronic vs electric underfloor heating for down there. I’d love it if you could describe what you actually ended up building!

  • Shawn December 1, 2014, 3:43 pm

    It might be too late, but never too late to retrofit:

    I had some clients whose house I sold a few years ago and with their set up they had a few valves that would reverse the flow of water. Turning off the system for summer would reverse the water flow under the house and then send the water through the hot water tank after, eliminating the stagnant water sitting in the lines.

  • Robin Whiteside December 3, 2014, 7:41 pm

    I had an open system for years, a do it yourself type I bought online back in 2003. I could write a book. But the short comment I will leave here is that it is always best to separate the systems (domestic potable from heating water).

    I found the best way was not a heat exchanger, but instead, to purchase a second tankless for domestic, and let the heat system run on a smaller cheaper tankless.

    The floor heat needs to run at 15-20 psi to preserve the quality of the pex. When you run a ex system on an open circuit with regular 55-70 psi tap water, you are asking for leaks and problems.

    I have a 2650 square foot victorian. I did this in three phases. First, the open system (leaks, tankless burnout, and risk of bacteria). Second, I used a heat exhanger, which solves the leaks and bacteria, but cost 20-30% of my efficiency. Then third, I used two tankless heaters–one runs all the time real steady for the floor heat, does not cycle on and off, and it’s a smaller unit 160k btu. The other tankless gives me mucho endless water.

    When I shared a tankless with a heat exchanger my gas and electrical use was very high. When I switched to Grundfos Alpha pumps, the electric cost went down by 70%. When I added a second tankless for just heating, and had the old one for domestic water, my gas bills plunged about 40%.

    Heat exchangers cost 20-30% in efficiency. Plus you work the tankless to death and it cycles on and off, which kills them after 3-5 years. No biggie, because replacing a tankless costs about $800-1000 per unit–that is cheaper than repairing and maintaining a high efficiency boiler.

    My two cents.

    Oh, and PS, radiant systems with multiple zones surely should have a low loss header so the flow is equal. This is beyond CRUCIAL. Primary secondary plumbing is a must, and a low loss header is the best way to accomplish that.

  • Andy December 27, 2014, 1:31 pm

    I might be grabbing at straws in, but I have a question. I am in the process of buying materials as they become available at the cheapest prices, to build a grain bin home for my family. I would like to use radiant floor heat and I’m also looking at going off the grid. One of the options I am considering is installing a wind turbine air compressor and storage to go with it. My question is this: is it possible to use a pneumatic pump, running off the stored compressed air, to pump my system?

  • Gary Heron February 24, 2015, 12:17 pm

    Hi, I am just in the design phase of my ‘green’ home and wanted to throw an idea out there for scrutiny. :)

    It has always bothered me to heat room in my house that are not in use. This idea of an electric ‘on demand’ heater made me think, why not make each room a separate radiant floor loop with its own heater hooked up to a programmable timed wall thermostat?

    The house is going to be on grid, but with over 50 solar panels on the roof so I should never need to buy electricity. I figured I could use electric on demand heaters like ‘Bosch Tronic 3000 US7’ or different sizes depending on the room size.

    Any thoughts?

  • Drew Gauley August 15, 2015, 2:19 pm

    Hello Mr Mustache,
    Great article and perfect timing for a little job I’m hoping to do. We’ve got a 1500 sqft concrete pad that is slated to have a bathroom and 3 rooms built upon it. I’m hoping to build the rooms first (since we’re ready to do that now) and add hydronic radiant floor heating by pouring an additional layer of concrete after the fact. I know this isn’t ideal but wondered if it’s even possible or advisable…
    A fellow beginner,

  • duncan cairncross October 1, 2015, 3:23 am

    I made my own hydronic system
    Couple of things
    (1) You don’t want hot water in your system – I didn’t see it on your list of parts but you need a “Tempering Valve”
    Here (NZ) they are used so that the hot water can be above 65C to prevent bugs but the hot tap is less than 50C to prevent burns
    The tempering valve adds cold water to the very hot water so the tap just give nice hot water
    You use a tempering valve so the feed to your underfloor is only 35C – too hot is bad
    (2) Because you only need warm water you can heat your water with a heat pump
    A heat pump heats up by a deltaT – the less the temperature it has to increase the greater the efficiency (more heat)

    I have used a old heat pump (free) two liquid to liquid heat exchangers ($500) – which means I can heat my whole house (165m2) with less than 1Kw of electricity!

    My ground source to feed energy to the heat pump cost about $1500 – $1000 for the double walled plastic pipe and $500 for the digger (same time as he dug the foundations

  • Eric Peterson February 24, 2016, 11:00 am

    I read a New Yorker article about you where they said you installed your own boiler.
    I did the same, also ordered from Pex Supply.
    My setup is not radiant as for your house, which did not make sense for our situation as we have cast iron free-standing radiators and baseboard units.
    I find that our lifestyle, while not as frugal as yours, does share many common observations and practices.
    I now hope to read more about your approach to a frugal lifestyle.

  • Gary February 25, 2016, 6:56 pm

    I’d like to share an update to all this DIY thread. If you are going to do radiant at all, I highly suggest you stay away from subfloor staple up systems. Go with Warmboard.

    Recently I added 1600 square feet of radiant heat space in my upstairs that had been old school direct vent heat. The difference in swiftness of the heating (the whole place heats up in less than a half hour) and quality is amazing, and the bills to heat that space are about one third what they are to heat my staple up downstairs (which also takes about 3-4 hours to come up to temp).

    This is a huge money saver over the long run, compared to all the waste you’d have if you did staple up systems. Initial cost is high, but remember, you are going to have this system for many years. Warm board pays for itself in a year or two, plus it can be used for remodels like I did OR structural plywood sheathing.

    Just my two cents. I will never do a radiant system without this warm board product, ever again. The difference is really astounding.

    • Mr. Money Mustache February 25, 2016, 8:01 pm

      Cool, thanks for the update Gary! While I didn’t have the option of top-of-floor installation myself (because I wanted to keep the vintage 1950s flooring), I would probably do an embedded-in-concrete/gypcrete install if I were building a house from scratch.

      I totally believe you with the heat transfer speed, but I am curious about the efficiency difference. Where do you think the energy is being lost in the lower floor installation?

      If you have a wood floor with R-1.5 resistance above, and insulation of R-13 below the tubes, it seems like you’d be forcing 90% of the heat through the floor. And some of the remainder would even be reclaimed through heating the crawlspace, which has insulated exterior walls.

      If you read my follow-up article, you’ll see that I think my system ended up reasonably efficient. But the slow heat transfer is still slightly inconvenient for someone like me who likes to have the temperature go down at night and when we’re out of the house.

  • Dave v March 14, 2016, 6:52 pm

    Nice blog and article. Wish I had seen this before completing my radiant system last year! We’re close and I did all the work myself (i have a mustache too :-)) but had a full unfinished basement to work in, but alas, I wasted the $2500 and got an Argo electric boiler. I’m also in CO (7600 ft) and our electric bill, even with an 8.4kw solar system, went to $190 per month from $0! We have a wood stove that pretty much relives the furnace of all duty, but the edges of the house get cooler than the 60-63 deg we maintain and are comfortable with.

    Since my system uses PEX (aluminum band too), it looks like I can simply add the loops for the cold/hot water, place a one-way valve and be ready to go with clean natural gas. I have to do some more research on the temps and circulating pumps to be sure it will all fit together.

    The radiontec site cited earlier is helpful as well.

  • Alex April 27, 2016, 2:30 pm

    Very nice article, Thanks. I was wondering if you could help me with this question.
    Couple of years ago we’ve installed ¼ pex tubing in basement ceiling, to warm 1st floor porcelain tile floor. Tubing are attached to the plywood with an aluminum transfer plates and insulated. So, pex tube heats plywood, then ½ inch cement board, then thinset and finally porcelain tiles. This is attached to Navien tankless water heater with the mixing valve so the max temperature is about 120F. We are in NYC area. Very disappointed with this, it is not working as expected. When outside temperature is below 30F, the system is running non-stop, the max temp of the room is 68F and tiles are not that warm.
    I am thinking to remove the mixing valve, to use 160F-180F water temperature for PEX tubing. Do you it will work? Will it damage or bend the subfloor? I am not sure what type of plywood was used ½ inch or 5/8. Generally, what is the max water temperature can be used?
    Thanks a lot.

    • Mr. Money Mustache April 28, 2016, 8:43 am

      Hi Alex, I noticed the same thing after my first test: 120F does not result in a very warm floor above. So I raised the temperature to 140F, and now my wood reaches the mid-80s. Very nice on the feet!

      160-180 could get a little risky: you’d at least want to make sure the PEX is rated for that temperature and pressure, and watch for deformation in your floor.

      Also, it helps to make sure you have insulation below the tubing to lock in that heat rather than radiate it into the basement as well.

    • Dave April 28, 2016, 12:27 pm

      1/4″ PEX might be undersized for your space. I would look at 1/2″ minimum. Also look at the spacing on the transfer plates to ensure maximum transfer. Most PEX is rated up to 180; some to 200 or 220.

  • Alex April 30, 2016, 5:00 am

    Thank you for your feedback!
    Unfortunately 1/4 pex was used. Will try to replace the mixing valve, to raise the temperature. If it won’t work, then will have to run iron cast radiators on the first floor.

  • Alex May 4, 2016, 7:50 am

    Thanks Dave & MMM!!!
    Actually, I was wrong. I have 1/2 pex installed and this is rated for high temp. My plumber changed the mixing valve, I run first test overnight with 135F and noticed huge difference, the floors are warm and room temp is 77F. Can’t run full test yet, since it is now 50F outside. Hope, it will work winter time. Will raise pex temperature as needed.
    My concern is subfloor. What do you think the max temperature be used do not damage the floors? 150F?


  • Aliea July 11, 2016, 10:08 am

    Been trying to figure out if I can use steam and its pressure to essentially ‘pump’ my water through a small space equivalent to a common master bedroom space. Questions I’m having are: what kind of contraption can I use to seal the water in and boil it from below, how big does the contraption have to be, what amount of pressure per square feet.

  • David July 24, 2016, 7:05 pm

    Radiant is becoming the dominant heating systen in new construction around here. Most contractors don’t like to pour a slab without radiant heat tubes even if it’s a garage that won’t be heated. I have seen systems that use boilers, condensing boilers and 50-80 gallon water heaters. In my own house I use a 50 gallon oil burning water heater. I don’t buy #2 heating oil. I make my own biodiesel and burn it to heat my house.

  • NDG October 12, 2016, 11:59 am

    MMM, I am getting into the nitty gritty of installing this right now! My not-quite-so-interesting question for you is whether it matters if the expansion tank is before or after the temperature and pressure relief valve, having already made clear that it should be before the pump. Thanks for your time – I know this is an old post! Will let you know how everything works out this Michigan winter…

  • Hotsauce1121 November 26, 2016, 4:25 pm

    MMM – awesome article! Thanks for putting so much effort into it. I had been considering engineering my own radiant system for some time now and this article has inspired me to go ahead and start the project. I do have two questions.
    1. What is the purpose of the “Main” thermostat in the diagram just above the water heater? I would think that between the zone thermostats and the controls associated with the Delta-T controls in the circulator pump any additional thermostats would be redundant.
    2. The diagram calls out a pressure regulator valve next to the cold water input but I was not able to locate a simular item in your Bill of Materials. Am I just missing it?

  • Gregory Cornelius December 9, 2016, 11:19 am

    What does everyone think about adding this above floor, or even in a wall? Rip 1/2 plywood into strips 5″ wide, add the aluminum, run the pipe down, put another 5″ wide plywood section and repeat until the whole floor is done. You would then come back and have to cut a 5″ diameter semi circle for the ends when the pipe bends to the next run. Then you can add cement backer board and floor tile or another flooring option of your choice.

    All options the same it should increase the heat output being closer to the flooring right?

    My house i am planning on the flooring. Doing this above might be easier than working in a craw space.

  • Andrew Jagniecki January 30, 2017, 8:30 am

    Hi, I have a project where I would like to heat a small concrete floor area 11 x 26 feet. I have a roll of 1/2 inch PEX insulated in the concrete. I would like to run a closed loop of antifreeze maybe heated by a small on-demand water heater using L P gas. Is this possible?

  • Paulo Ney October 22, 2018, 8:51 pm

    Would you consider reviewing the sketch of your design, and reposting it? It will be easy to do according to to the steps that have been remarked as wrong and that you have even corrected on your own machine – like for example – the position of the expansion tank. I guess quite a few people pick the sketch up and do not realize that some mistakes on it have been corrected. The ones I would consider important are the tank and the check valves.

  • Katni January 22, 2019, 8:47 am

    I designed a radiant baseboard system in our enormous country house in italy. It was going to cost me a fortune to ship such a system 14 years ago from the US.
    Not difficult at all. Copper looped pipes along all exterior walls and a few Internal walls. Had aluminum cut and bent then painted by our body shop friend to act as the baseboard cover. Tankless instant boiler has separate water heat control. Plenty of zones on the manifold.
    And now we are adding a thermo/hydro pellet stove. I”m also about to add a couple of meters of base board to increase heat in 2 rooms. (mods not so easy with under floor)
    We are super happy…. No drafts.. even heating, nothing ugly to look at and pellets are cheap.
    Only negative is you don’t get such Instant control, thus the ceramic pellet stove. 15 minutes and the main living area is Hot in dead winter while the entire system starts heating.
    Congrats on your initative.

  • Kathi January 22, 2019, 8:55 am

    Oh.. Also I have a separate cold water inlet straight from our well (with bypass) which I intended to run through the system on the summer to drop the temp by a couple of degrees. Turns out we don’t need it.

  • Chuck September 14, 2019, 1:52 pm

    Great post. Now, while I’m a few years late to the game, your project raises some questions. I just renovated my home and was, like you, talked out of hydronic radiant heating. Instead, I had hydronic air handlers for forced hot air installed. Now, I am looking to retrofit–add a few radiant floor “circuits” from my basement before I finish it. Can I simply “tee” off my hot water line going to the air handler? Off the tee, add a circulating pump to a manifold that runs hot water to radiant flooring in select rooms above?

    If anyone is still reading this, I’d love some input.

    • Mr. Money Mustache September 15, 2019, 10:23 am

      Hey Chuck,

      Yeah, I think that would probably work. In general, as long as you have hot water (140F) circulating anywhere, you get a good amount of heat out of it. The variable speed pump is what makes it all work relatively well.

      Since writing this article, I went on to build a detached studio building with a side-branch of floor heating embedded right into the concrete floor. I turned on the new circuit and it just magically ended up nicely heating the studio quite well – it didn’t even need its own separate zone in the end. But the good part is, you can always modify the way the circuits are used later. The only hard part is installing the tubes in the first place.

      • Chuck September 17, 2019, 7:10 am

        Thanks for the reply. Since I’m Mr. Piecemeal, I’ll be chipping away at this project over the next few months. I’m thinking of tackling the hard part first anyway– rough everything in–then figuring out the best setup for distributing the water off my current system. A little magic wouldn’t hurt, either.

  • Sergio June 10, 2020, 12:37 am

    Hello I can see that I has been a few years since you posted this, but I wanted to ask you how everything has been going with your system. Also wanted to ask you, have managed to have each individual zone with it’s own thermistat?

    • Mr. Money Mustache June 11, 2020, 7:10 am

      Still works great! .. although it’s still all on a single zone – the house is open and small enough that the heat seems quite evenly distributed throughout, so I never took the extra step of multiple thermostats. Those would probably be most useful on a multi-story house.

  • Jorge Brandão July 8, 2020, 12:17 am

    Greatings from, Portugal and thank you for the great post.
    I still couldn’t read all the comments so I’m not sure if this questions is repeated. If so, I do apologize.
    These are my doubts:
    1. Have you placed any insolation between the tubing and the ground?
    2. In the circuits, how distant is a line of tubing from the contiguous one?
    Thanks and I hope my English is reasonably understoodable.

  • Joe February 24, 2021, 8:46 pm

    I cant believe its been 7 years since I first read this! I just thought if it again tonight when a friend shared this video of an arguably stylish wood-burner that can be used as a tankless water heater.


    Thanks for keeping up this blog over the years! Your post back in April really helped me pre-callibrate for 2020.


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