Radiant Flooring

August 15, 2011 — 33 Comments

Currently I am working on three projects that all have radiant floors in some of the rooms. That might not sound that unusual but I do live in Texas and we are going through one of the hottest summers on record – and yet people are asking for radiant floors … that’s because radiant floors are wonderful. I still wonder if I would put them in my house … I am not a barefoot person inside, not sure why but I like to wear slippers. My wife on the other hand hates having anything on her feet and constantly walks around barefoot. I know she would love to have nice warm floors in the colder months so that she could forego socks or slippers – sort of a big deal since our house has concrete floors.

Since I tend to get “wordy”, I thought I would have some G-Man from the Department of Energy describe the different types of radiant floor heat – it won’t be as interesting but you’ll have a firm grasp of what you have to work with.

Legalett Air Heat Radiant Floors

Air-Heated Radiant Floors

Because air cannot hold large amounts of heat, radiant air floors are not cost-effective in residential applications, and are seldom installed. Although they can be combined with solar air heating systems, those systems suffer from the obvious drawback of only being available in the daytime, when heating loads are generally lower. Because of the inefficiency of trying to heat a home with a conventional furnace by pumping air through the floors, the benefits of using solar heat during the day are outweighed by the disadvantages of using the conventional system at night.

Infloor Radiant Heating on floor

Electric Radiant Floors

Electric radiant floors typically consist of electric cables built into the floor. Systems that feature mats of electrically conductive plastic are also available, and are mounted onto the subfloor below a floor covering such as tile. Because of the relatively high cost of electricity, electric radiant floors are usually only cost-effective if they include a significant thermal mass, such as a thick concrete floor, and your electric utility company offers time-of-use rates.

Hydronic Radiant Flooring

Hydronic Radiant Floors

Hydronic (liquid) systems are the most popular and cost-effective radiant heating systems for heating-dominated climates. Hydronic radiant floor systems pump heated water from a boiler through tubing laid in a pattern underneath the floor. In some systems, the temperature in each room is controlled by regulating the flow of hot water through each tubing loop.

Out of these three systems, we only use the electric radiant systems. I can’t imagine using the air-heated ones – it seems like something Dennis Hopper would have come up with and wildly inefficient. The DOE tells me that hydronic systems are very energy-efficient but we don’t use boilers in Dallas and I think the DOE is full of baloney. Since we only are looking for “spot heating” (warming just the bathroom or kitchen) instead of “sole source heating” (heating your entire house), we are in a turn-on & turn-off situation … and the cost of running these small areas just a few hours (at most) a day is vastly more cost-effective.

There is also product and installation cost difference; in a typical bathroom we might spend $800 on the electric system where a similarly sized hydronic system might cost $4,000. Despite what G-Man Bill tells me, electric radiant heating systems are the only type we ever use. There are several different brands we specify – Nuheat, Infloor, Suntouch, etc. and they are all good products although I’m not a huge fan of using the  mat systems. As far as the degree of difficulty for the different types of  installation, I suspect the contractors have their preference as well.

This is a view looking down at a typical electric wire layout (Nuheat and Infloor offer these types of systems). There is a strap (shown below as a gray bar) that you adhere to the sub-floor and then weave the wire back and forth to create your area of coverage. The heat will not extend more than about 2″ from the wire so that is a consideration for the spacing and general layout pattern. The good part about this system is that you can control the exact areas of coverage and the installation procedure doesn’t change for irregular areas.

Infloor radiant flooring sample layout

Another variant on the electric cable and strap system is the electric wire preset into a mat mesh. If you have a really simple layout than this system work fine. Some of our bathrooms run a little (cough, cough) larger and these mats only come in predetermine widths. For example, I have a 7 foot wide area to be covered and my mats will only accommodate 6′ so the solution is to widen the gaps between the mats (boooo). I am over-simplifying things but you get my point.

Suntouch Tape Mats


Suntouch Tape Mats sample layout

Another reason I don’t love the mats system is that the area represented in the above drawing just in front of the shower. For this irregular area, you are supposed to cut away the mat mesh to expose the heating wire, and then set the wire in place using … hot glue. What?! The only time you should be using hot glue is for building architectural models or trying to attach your hair piece (I think… might be wrong about the hair piece).

Both system come with a sensor that you connect to the heating wire during installation – it’s called a ‘Loud Mouth” – I’m pretty sure it just blares a tone rather than talking endlessly about the semi-semi-pro baseball league team he plays on and how they got screwed out of making the playoffs for the 4th year in a row and how his batting average is crap but it’s not his fault because Coach has him batting 8th in the lineup and…..

Loudmouth currency detector

All this thing does is monitor the electrical current in the heating wire during installation. That way, if something goes wrong and the installer accidentally cuts a line, you’ll know it immediately and they will know where to fix the damage. This is a lot better solution than trying to find the problem after the wires have been covered up with the finish floor material.

So there you go – an actual informative post written on an actual architectural product – wasn’t it fascinating and entertaining? Yeah, I know, boring stuff … but I need to know all about these things because clients want them and so far every person who has them in their house is in love with them. I’ll try to make these more interesting in the future.


Bob-AIA scale figure

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  • Pingback: Common Sense Building: Making Sense of Radiant Heat (FAQ)()

  • Jeanine H

    Wow, I just caught your response to the first comment I wrote to you regarding heat–that led me here! Thank you soo much for respons as we’re working on a heating project like this AGAIN come August Cheers Bob to fantastic informative posts!

  • Pingback: Common Sense Building: Making Sense of Radiant Heat (FAQ) | The HTRC: Homeowner's & Trades Resource Center()

  • Electrical heating mats for under floor heating systems can be placed on a wood sub floor. I have seen this many times before.

  •  I think roof heating is also not a bad idea. It can be also used for cover the specific space for heating. Any way thanks for sharing this brilliant post with us. I got some new information from this post.

  • Snooze…But…we have one of these in our Boulder house. It’s wonderful in the winter. Sadly, I don’t live there any more. But the tenants love it.

    • snooze is right … the temperature is always nice and toasty – perfect for a nice little nap.

      That is what you meant right??

    • snooze is right … the temperature is always nice and toasty – perfect for a nice little nap.

      That is what you meant right??

  • Anonymous

    Great read Bob!

  • Tara_imani

    Hi Bob,
    This was so ironic to see this topic today as just last night I was talking to my husband about radiant slabs. We had a client years ago who was actually the creator of a radiant slab system and asked the southern California firm where I worked to incorporate it into the design of his new house.

    I have not heard radiant slabs mentioned again on specific projects until your blogpost today. I had wondered what happened to the technology.
    The reason I’d brought it up last night was to ponder whether this technology could be used-safely and efficiently- to heat indoor swimming pools. I’ll have to research this. Does anyone here have any feedback on this idea? My friend has a large indoor pool that’s enclosed by a glass trim. It is here in Houston. The pool is always freezing cold, so its not much fun to use but beautiful to look at. They said it costs a small fortune to heat it. So, I thought of the possibility of radiant slabs– yrs, its another luxury item. Just curious!
    Thanks for bringing this topic uto the fore.

    Have a great day,

    • Tara_imani

      Sorry for the typos- still getting used to this Droid 4g. The indoor pool is covered by a steel framed glass atrium.

    • Tara – you should contact Allison Bailes (tweets as @EnergyVanguard:disqus 
       – here is his website: http://bit.ly/qIX7ms )
      He knows his stuff and would be a good person to start talking with to find your answer.


  • We have used hydronic radiant in a cement slab, R-32 SIP’s for walls and R-60 in the ceiling area. The combination works well as the hot water is heated by a Polaris water heater- very efficient. Our 2200sq’ house is heated to an average temp of 74 for 8 months- Vermont- costs on average $800-1100/yr. for propane including stove and auto back-up generator.

    Next house will use a system that has a sand heat trap with radiant tubing laid out in the middle of the sand trap.  The sand trap will be insulated on all sides and be 2′ thick. On top of that will be the conventional slab with hydonic radiant heating. This should reduce energy use/costs even further. The tubing in the sand will gain its heat from a solar panel(s).
    We’ll see how that goes.

    I have heard about using a system with Hydronic radiant in warmer climates that works to cool the slab by taking out the gathered heat. I would think that heat could be recycled using a A/C type system to transfer that BTU heat into thermal cooling , sort of the reverse of geo- thermal systems.

    I haven’t looked at that thoroughly but I’m sure some has some good advice there

    • Wow – that is some serious performance you are going after. At that level, I think the owner has to be interested in more than just saving money on their energy bills. What you are doing is making a statement on responsibility and consumption.

      Way to go Todd!

  • Girlfuturist

    Great post. I think the BEST reason for radiant floors is not having sinus-drying head-cold-inducing hot dry dusty air flying around the house in the winter. This is a big deal in cold dry climates like winters in Idaho. I always get a head cold the first time we turn on the heat in the fall, humidifier not withstanding. My parents have the hydronic version in their house in France, and it’s wonderful. Guess I’m just going to have to build my own house. Or buy an old one with radiators 🙂 Sigh.

    Even if I can’t do the whole house, I’ll definitely never do another bathroom remodel without putting it under the stone/tile floors.

    • Another reason – the old “sinus-drying head-cold-inducing hot dry dusty air flying around the house in the winter”

      We are definitely seeing more and more requests for this sort of feature in our homes.

  • I designed a house in Minnesota for my parents and hydronic radiant heat is becoming very common in that part of the country.  Also the local power company will give you a peak power rate deduction if you install a well insulated system (i.e. rigid foam insulation and a bed of sand under the slab).  And speaking of insulation, these conversations should always be made in the context that the house is already insulated with something better than batt insulation to begin with, making the system even more efficient.  Nothing makes me more angry than seeing people through their money away on expensive technologies because they have a poorly insulated house.

    • I agree, hydronic is the way to go is you are doing sole source heating. We also go to great lengths to insulate a house properly, even down to detailing how the studs should be laid in the corners so there aren’t large un-insulated gaps. 

      Thanks Kevin

  • Dave Rizzolo


    We have clients often ask for electric radiant systems and we then have to spend some time explaining what their limits are. 

    Up here in the northeast we refer to electric radiant systems as “floor warming” and not as “radiant heat” as we find they come nowhere near producing what would be required to heat even a small bathroom space in the winter. Hydronic systems are needed to actually provide  comfortable space in the winter.

    • Dave – you are absolutely correct – and we only use these system to warm floors and not to actually heat the home.

      • Julia Billen

        Not true – electric floor heating can be used as a primary heat souce – I live in “sunny” Illinois and have used nothing but electric radiant heating for 7 years now.  This is a common misconception with hydronic vs electric but it is far from true. Also, my house is large – 8,000 square feet – not including my above ground basement where I use electric radiant heat on a concrete slab as a primary heat source.

        • Hi Julia, I should have been more clear. You can use electric radiant heat for sole source heating but we typically don’t recommend it due to the cost of electricity. I believe most people go with hydronic for large scale heating simply because there are elements in place that make it a more cost effective solution.


        • Gerry

           Julia, I am thinking of doing what you have done, but they are telling me the electric bill will be high (Northern California).  What is your experience with electric costs of your radiant system?  What if I am also installing solar pv on the grid ?

  • Anonymous

    Radiant floor heating with electricity is 100% efficient. Well, if you ignore distribution losses to unconditioned spaces or the ground. And if you ignore the tremendous amount of energy that was lost at the power plant that made the electricity. (About 2/3 of the energy of coal is lost.) Also, please ignore that a heat pump can turn electricity into heat at an efficiency of 200-300%. 

    I’m not totally against using electricity for radiant heating systems like this, but it’s got to be a small system that’s offset by not using the central heating system, as you suggest above. Also, make sure that you don’t design it in a way that it’s also unintentionally heating the garage or the ground or the outside air.

    Have you looked at using solar thermal collectors for the radiant heat, Bob?

    • Yes, we’ve looked at solar thermal collectors – and they don’t get the job done when there’s demand. People want the floors warm when they get up at 6am to take their shower and guess what? the sun hasn’t been out long enough to make this happen. The time to recoup the cost to add a storage system makes this a silly conversation. (“It’s a great system and you’ll break even on the setup and operational costs in 27 years!!”)

      Also, I think you must be down on electricity in general because your stats about the amount of energy it takes to produce that electricity aren’t specific to electric radiant heating. Since we don’t use toaster technology to heat the entire house, you are going to have a hard time convincing me that there is a more cost efficient way to add this (admittedly luxury) feature to these relatively small locations.

      • Anonymous

        No, I love electricity, Bob! I think it’s one of the greatest natural phenomena that we humans have ever harnessed. It’s useful for so many things because it’s a highly organized form of energy, and to turn it into heat is a tremendous waste in most cases. I do agree with you that it’s useful for small applications. I like toast, for example, and if a small electric resistance heating system offsets use of a larger central heating system, it’s OK. But it comes with a hefty cost when your electricity is made by burning coal.

  • Here in Portugal thei tend to be widlly useded, specailly wather heated, especially because we have very cold winters and warm summers but lots of sunshine: so, wehave execllent conditions to use solar panels. And in our building codes they are mandatory and electible to special credit concessions.

    • José,

      Your environment seems better suited than ours here in Texas. We don’t used water/ solar because the time of the day we would want to use it is generally not very sunny (i.e. early morning and late evening). It is a great system and one that I hope more people start taking advantage of in their homes.


    • José,

      Your environment seems better suited than ours here in Texas. We don’t used water/ solar because the time of the day we would want to use it is generally not very sunny (i.e. early morning and late evening). It is a great system and one that I hope more people start taking advantage of in their homes.


  • Alexandra Hanson

    I lived in Minnesota and we had radiant heat in the master bath.  Many winter (aka not July) mornings when I made my cup of coffee I wished that we had installed them in the kitchen.  

    Let me get this straight, you are supposed to use hot glue on a product that heats up.  Speechless. 

    • Alexandra,

      Yes, I was a little surprised as well but on page 10, table 6 of the installation manual labeled “Fill-in Technique” it reads:

         “Use hot glue to attach wire to the floor”

      Do I get points for reading the installation manual? … I totally should.

      Thanks for commenting-

      • Steve May

        I would like to think that the hot glue is just there to hold the wires in place until you get the finished floor over the top.

        • it is – but compared to the looped wire systems, it seems like a oversight in the installation process.