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Ceramic tile is a desirable choice for bathroom floors because it is durable. Among its cons is the fact that many people find tile cold. For this reason, radiant heating under bathroom floors has become a popular upgrade. Here’s a look at the best options for warm bathroom floors and how much energy this comfort requires.
In general, radiant-floor heating offers some advantages. Overall, it is more efficient than baseboard heating, and it can be more efficient than forced-air heating in smaller areas with conventional ceiling heights. Hydronic, or water-based, radiant floor systems use the least electricity and can be combined with solar panels and ground-source heat pumps for maximum energy efficiency. People with allergies sometimes prefer radiant heat because it doesn’t distribute allergens like forced-air systems do. However, hydronic systems are expensive to install.
All radiant-heating systems have one characteristic in common. Namely, to warm a room, they must remain on continuously. Radiant floors for underfoot spot-warming in areas like bathrooms generally function as a supplemental heat source and have an advantage. These heated floors serve their purpose sporadically and are designed to warm up quickly without consuming too much energy.
ThermoSoft specializes in in-floor heating and offers both mat and loose-cable systems. They are categorized by flooring types that include tile, stone, wood, laminate, vinyl, carpet, and concrete. You may have seen their electric ThermoTile mats, which glue onto the subfloor with thin-set, and then ceramic tile lays directly over the top. The system consists of a thermostat with a floor sensor, so you…
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32 Comments
The resistance floor mats will likely burn out in time. I agree with most posters on GBA that in floor heat is not appropriate for a highly efficient home. Where I have seen hot water in floor heat work quite well is in a CO log home. Due to the rather low R-value of the log walls and the heat loss that comes with it, the floor temperature is kept somewhat above 70F. This house is at about 8,000 feet above sea level SW of Denver so the heating season is significant. The full basement has an insulated slab with PEX tubing and the above 2 floors have wood framing with PEX in gypcrete. There are 9 zones as I recall with a natural gas boiler. A very comfortable house to be in. The rest of the house is highly insulated, log walls are what they are, kind of expected in the mountains of CO. This house also has a masonry heater, a work of art in my opinion.
I really wish that the folks saying things like radiant floors are "not appropriate for a highly efficient home" had actual experience living in homes of this type. There are lots of design, execution, and financial reasons to not do this, but my own house is proof that radiant floor systems can work well in tight, well insulated buildings, while providing amazing comfort. The assertion that during the heating season "the floors are never warm under foot" is also a gross oversimplification of how these systems perform and can be configured. Like at least one other GBA member, our house is micro zoned and we basically heat our house in the winter mostly through the bathroom floors (bathroom T-stats at 70F, the rest of the house at 66-68F). This means the bathroom floors are always pleasantly warm. The floors in the rest of the house are also never cold so we walk around barefoot year round without even thinking about needing something on our feet to be comfortable.
As a builder I have to weigh cost to value. If one is building a highly efficient home and wants in floor heat that is fine. If it is a redundant heating system because you need summer dehumidification then I have to question the worth. I finished a townhome for friends in 2010 in MSP. We considered a separate boiler for hydronic heat for the lower level. The cost at that time was about 15k additional. My suggestion was to use sub slab rigid insulation and zone both upper and lower levels at a cost of 4k. This is what we went with and the comfort between levels was great. The lower level concrete floor was exposed and because of the insulation was very near room temperature. What was very noticeable about the townhome, open between floors, was the lack of stratification. This is what you get with adequate insulation levels and building airtight.
Saying that radiant does not pass the cost vs. value bar for a given project is very different than an absolutist sounding position of "radiant is never appropriate". I have no problem with the former, but the latter eliminates the possibility to explore what may be the right solution depending on the goals.
Our house heats and cools through the floor using a single air to water heat pump. If we needed dehumidification, we'd add a single hydronic fan coil running off the same system at the top of the second floor. There is no need to add redundant systems when radiant is designed well. I don't have enough information about the project or your clients to claim that adding radiant in your town home project would make sense, but you certainly could have done it without adding a boiler just for the floor.
My first post described a Colorado home in the mountains where in floor radiant was the way to go. Because it is an arid climate no AC is needed. Natural gas was available with a line running along the access highway. I have been in the house in winter and it is very comfortable. Could I sense the warm floors, I don't know.
The point others have made about in floor radiant is the floor temperature will not be much greater than the thermostat setpoint. The floor becomes a giant radiator and it only takes a couple of degrees beyond the setpoint to offset the heat loss of the building envelope.
Seems reply depth is limited in GBA, so I have to reply to myself.
The Colorado home you describe cannot be called a high efficiency building. It is an example of a "classic" application of radiant floor heating in a building with high heat loss. So I interpreted it as a contrasting data point fully consistent with your statement that "floor heat is not appropriate for a highly efficient home".
"The point others have made about in floor radiant is the floor temperature will not be much greater than the thermostat setpoint."
Sure. But what does that mean for building occupants? For those that have never lived in such a building, there is an assumption that the floor temp delta is "imperceptible". On the contrary, just having our slate tile floors at room temperature means the floors do not feel cold even if you are barefoot. With a 2-3F delta, they are pleasantly warm. On really cold days, the delta can hit 8-9F (again because we predominantly heat the building via the subset of floor area where we want a noticeably warm floor) which is "toasty". This is in a .6 ACH50 structure in Boulder, CO with R35 walls, R50 roof, R30 crawl space walls, and R20 under the slab in the crawl.
A reply to Justin Gibbs (Oddly, when I click on the reply icon to Justin Gibbs message GBA Says I’m replying to another individual )
It seems as though you are in a great place to give a firsthand account of living in a well insulated/ air sealed house with a radiant floor.
I was just thinking about heating small areas of a slab so those areas would feel warm, so your info is very timely. Could I trouble you to go into further detail about what percent of your floor is actively heated ?
Have you looked into how different temperatures of the floor feel, when in contact with bare skin?
Thanks!
Ben
I originally planned for radiant heat in my highly efficient home (not quite passive house but close.) I read all the articles about how low the water temp would be and that you wouldn't feel warmth. Now some here are saying it's not true. I guess the jury is out. But the other issue is the slow reaction time. I was going to use warmboard to help improve that, but it was still potentially an issue. My CZ6 mountain town is full of multi-million dollar homes that run their floor heat AND air conditioning in winter because when the sun is not out you need a lot of heat, and the minute the sun comes out the homes overheat. The final consideration was having to minimize rugs.
The system was at least $100k. And it still didn't have cooling, which I didn't originally mind because I hate AC and historically there's been about a week or two a year when it was unpleasantly warm, especially because it cools down every night. But then while I was designing and building we had 2 very hot summers. Climate is changing. I really felt the need for at least some AC going forward. So that would have been an additional cost and probably a fair high one to get distribution.
Instead I ended up with a high end Daikin VRV mini-split system with 6 heads for $40,000. (I didn't want a ducted system due to health issues.) This left some rooms unconditioned but we think they will be fine and we have the ability to bring some additional heat to them if necessary. So the last issue was the bathrooms. And yes, we did put radiant heat in the floors. I am not expecting to have to use it much beyond cold nights and early mornings.
Fernando,
"Overall, it is more efficient than baseboard heating... Hydronic, or water-based, radiant floor systems use the least electricity "
"It becomes impossible to compare the energy efficiency of electric-resistance heat since all these systems work at 100% efficiency. In other words, all the incoming electric energy becomes heat. The cost difference in running the system comes with demand wattage (more powerful systems use more energy) and the local utility price. "
Can you maybe square the circle on these two comments? They appear to contradict each other - and the second one appears to contradict itself.
Another contradiction is the paragraph starting with "All radiant-heating systems have one characteristic in common. Namely, to warm a room, they must remain on continuously," followed by a discussion of systems that are used only intermittently and warm up fast. In fact, the ability to make occupants comfortable before the room overall is warmed up is one of the advantage of some radiant systems, particularly cove heaters and quartz tube radiant heaters. Radiant ceilings also tend to be faster than floors, because ceilings don't need to be as strong as floor and can be lower mass.
All I am saying, Malcolm, is that electric heating elements are 100-percent efficient (no loss in energy-to-heat) and hence the difference between different electric radiant systems is not inefficiency but rather size. The bigger ones use more electricity.
"Hydronic, or water-based, radiant floor systems use the least electricity..."
Thank you Malcolm. That section seemed all over the place. I think the real question is what does efficiency mean. Since the point of heating is comfort, efficiency should be thought of as the most comfort for the least money.
Since we're talking about floor heat as a delivery mechanism, it's only really the comparison to other delivery methods -- forced hot air, other hydronic methods -- that is relevant. The efficiency of converting the input fuel to energy isn't really relevant because it's distinct from the delivery.
I can remember when the claim was widely made that radiant floor heat created more comfort for the same amount of heating than other heat delivery systems, and thus was more efficient. There was never any scientific basis for the claim, and it seems to have been largely abandoned.
So how can a delivery system be inefficient? When it doesn't create comfort: the room is too hot, too cold, loud, or doesn't respond quickly to changes in the need for heat. Or the heat isn't going to occupant comfort, but is instead going out through the roof or windows or into the ground.
Radiant floor heat is conducive to greater occupant comfort, because it lends itself to microzoning. But there's no guarantee that simply because a system is floor heat that it's going to be optimized that way.
The new air to water heat pumps (electric) have COP reaching 3.8, so they are operating at much higher efficiencies than electric radiant. This coupled with aluminum plate emitters also make the hydronic systems more responsive, and operate at lower water temperatures than past systems. They also tend to keep the refrigerant out of the house.
William,
I understand (and of course accept) the argument that any heat pump powered system will be more efficient than electric resistance, but that doesn't have anything to do with whether that efficiency is then used to heat air, or water based radiant panels. What I'm not seeing is any evidence that water based heating itself is inherently more efficient, which is what I took Fernando to be saying.
Malcolm, properly designed hydronic distribution systems will outperform properly designed air based distribution systems every time. I'm speaking solely to the relationship of BTU delivered/watts consumed for delivery. John Siegenthaler has really opened my eyes to this concept, and I feel it can't be ignored. That being said, the added complexity of a hydronic system on top of a refrigerant based system is not always the answer.
AugieMarch,
I've come round to the idea that water based heating offers a lot more advantages than I had understood. I hope simple systems are developed and are widely adopted.
Cool! Me too. As an HVAC professional and enthusiast, I think both have their place. Careful design is key, like anything.
I have both oil fired/ boiler-fed baseboards and mini splits in a house with moderate air sealing and insulation upgrades. Most of this winter we have used just the mini splits for heat and they did very well. However, when my wife and I both got COVID a few weeks ago we switched on the baseboard to ward off the "chills"....because the baseboard hydronic heat is more even........less stratified. I love my mini splits but for comfort during heating season, hydronic heat is hard to beat.
Hello William and all,
We are in the planning phase for our retirement home and are very interested in learning more about air/water heat pumps.
Unfortunately I have not been able to find much experience based information on the web
and here in Maine I have not yet found any dealers to discuss with.
Seems like there is some experience in Atlantic Canada but not much on this side of the border.
Any references/suggestions appreciated.
Thanks,
Larry
Hi Larry,
Our 2017-2018 build combined a WarmBoard radiant floor system with a Nordic ATW-75 air to water heat pump to heat and cool the building. The building is in Boulder, CO - climate zone 5b. Our setup was designed by Harvey Ramer of Ramer Mechanical in PA.
I also have a warmboard application. But I do need a cooling system. My thought was a combiboiler for my DHW and warmboard. For cooling a normal Air Condenser & Duct Work. Are you saying a Heat Pump could take care of my hyrdonic heating and cooling?
@scsiguy thanks so much for the hardware and contact information. I reached out to Harvey today.
I am using Arctic Heat Pumps. They provide complete packages and will design your radiant floor system for you. Not installed yet but impressed with their knowledge and support so far. They claim heating ability down to -25C with their air to water heat pump and also claim to be able to do cooling in the summer with a dew point sensor.
http://www.arcticheatpumps.com
Ken
Have you completed your project? Is the Arctic system working as hoped? I'm also looking at their solution for a small project I'm working on.
I would also like to know how this turned out.
Our building inspector required a heat source in all of our bathrooms. We went with the Panasonic heated exhaust fans simply for the reason that it would be an easier fix if the heating element broke and we did not like the idea of having baseboard heaters. We toyed with the idea of radiant in-floor heating, really thought we would enjoy the warm feet aspect, but eventually abandoned the idea as we were worried about serviceability.
We tend to keep our home on the coolish side 18C = 65F. Hence our soapstone island feels quite chilly. It's where we love to sit & read/write.
Has anyone tried local heat to the island? Eg - https://www.warmlyyours.com/en-CA/countertop-heater
Or could one of the heating films described in the article be modified to warm a patch of cold stone to warm my forearms?
I've not tried that, but I LOVE our warm seat from Gallanter and Jones https://galanterandjones.com/
My Zone 7 home, built in ‘78, was provided with radiant ceiling panels in most areas and an entryway/foyer of 175 sf that is radiant floor. I have learned to keep that floor heat on because the architecture if the rest of the house is easier to enjoy if that space is not below 0 F. But they under built it; it stays on but in really cold snaps the temp drops. Maybe a rug on top would help.
I never cared about heated floors for the feel of it. However in my house we don't have ducts so heat distribution is the issue. (We have a VRV heat pump with 6 heads over 4100 sf.) The main thing missing was the bathrooms. So that's why we added underfloor radiant to those.
The commercial project we did a few years back involved a fairly large radiant project, about 4500 sq/ft on the main floor. However, we also had to install 5 air handlers in the same building for cooling and fresh air delivery. The main floor was an over-pour on an existing slab comprised of 2" of foam, steel grid, and 2" of concrete. Zone 7A with a very, very efficient envelope, also upgraded during a complete interior retrofit. We used a single Triangle Tube on demand gas boiler (with a redundant alternating spare) to service both radiant and air handler coils.
What I realised after looking at about 5 years of data from nine Ecobee3 stats, is that max efficiency in terms of gas use, was achieved with fairly aggressive night setbacks on the air handlers, and the radiant therefore spent a lot of time off. The 2" slab had a relatively fast recovery so I had be careful adding heat to it as the afternoon temp bump needed to be controlled. In other words, the slab actually needed to be a bit cooler to moderate daytime heat loading from occupants and passive solar. For that building, the only space that made sense for radiant (in retrospect) was the loading bay area which was insulated and kept at 8 C.
Doing it again, I could have significantly reduced the ($250K) mechanical budget, insulated the slab, and just gone with the air handlers which had to run anyway during the day for air exchange and AC.
In a tight home, with a well insulated slab, and external insulation, I honestly don't see the point of radiant. The floors will be pretty much at your set temp. Choosing flooring that is less conductive in a bath may further obviate a desire for supplemental warming for that specific application.
At my 110 year old home, the (old) supply duct that services the 2nd floor bathroom and adjacent bedroom runs under the bathroom floor and keeps it nicely warm to the bare toes :-) Setback recovery on the house thermostat is timed to the morning routine so that floor ends up seeing quite pleasant for morning showers etc. I bring this up as I suspect there are other approaches to differentially warm a floor section that we don't use as convention.
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