Hydronic heat – underfloor vs in-wall
Not asking for any individual project, but just to get a sense of people’s thoughts. My apologies if you aren’t interested in hypotheticals.
Underfloor heating remains popular in Europe, but in North America there seems to be an emerging consensus that underfloor heating provides too much heat for well-insulated houses. Plus, many people prefer wood floors to masonry.
In a well-insulated house, could in-wall hydronic work better? Instead of an entire floor being the heat diffusion element, interior walls or parts of several interior walls could serve. If those walls are smaller, then the problem of too much floor could be solved.
Also, it seems like an easier retrofit, plus many people prefer wood floors.
(I understand that it is possible run hydronic under wood floors, but it seems to have real downsides.)
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bsawers,
If you aren't going to get the benefits of a warm surface you touch, wouldn't it make more sense to go back to how hydronic heat used to be delivered, and put radiators on exterior walls where the heat is most useful?
Radiators take up floor space ( though modern ones are thin) and radiators trap dust. But if there’s a good way to remove dust, radiators are probably simpler than in-wall.
Wood floors work fine with radiant heat - the issue is when the water temp is too high. In a low load home, water temps would be lower and less of an issue. Wood floors have the other advantage of being lower mass, so more responsive than concrete.
Why stop at walls? Radiant ceiling panels are a thing too and supposedly have better BTU/hr/sq. ft. than even Warmboard depending on the floor covering. Also you don't have light switches, cabinets and pieces of artwork hanging from your ceiling so you should have more unobstructed surface area to utilize.
These below numbers are at the same 100 degF water temp and 70 degF air temp:
Warmboard = ~25 BTU/hr/sq. ft. below 3/4" wood flooring, or ~20 BTU/hr/sq. ft. below 3/8" carpet (without padding I'm assuming?)
Messana says to assume 24 BTU/hr/sq. ft.
Warmboard Source: https://www.warmboard.com/wp-content/uploads/2022/03/InstallGuide_Warmboard-S.pdf (page 37)
Messana Source: https://messana.tech/ray-magic/ray-magic-nk/
The thing about floor heat -- really any warming surface -- is that the amount of heat produced is directly proportional to the temperature difference between the surface and the surrounding room.
This seems basic, but it took me a long time to grasp. It's easy to get caught up in flow rate and tubing spacing and water temperature deltas and all of the other myriad details and lose sight that all of those things are ways of controlling the surface temperature.
A floor has a relatively narrow band of temperatures where you get the desired "radiant effect." Below about 80F you don't notice that it's warm. It might be nicer than a room temperature floor but that's it. Above about 90F it starts becoming unpleasant to walk on, particularly for long times. If your room is at 70F, you get a swing of 2x in output between 80F and 90F.
So you have a design challenge -- either size it so that at 90F it covers your design heating load. Design heating loads are set for the 1st percentile outdoor temperature, so if you do so 99% of the time your temperature will be below 90F, and a huge percent of the time it will be imperceptible. Or you can size is so that almost all of the time it's on -- say size for your median heating season temperature when the floor is at 85F. If you do that you'll have warm floors all the time, but you'll need some sort of other heating device for when it gets really cold.
I have both heated ceilings and floors (along with a few walls) in my house.
The floors are only in the bathrooms, it's nice under tile on bare feet. It's sized as I laid out in post #5, designed to be on almost the entire heating season rather than to satisfy the entire heating load.
Heated ceilings are great, it's very even, quiet heat, you don't even know it's on. I literally can't tell if it's 60F or 30F outside. It helps that my house is new and tight and well-insulated. The big disadvantage of ceilings is that you need more square footage to get the same heat output. For the same surface temperature you get about half the heat output from the ceiling. When I tell people that I have heated ceilings their reaction is often, "but doesn't heat rise?" Well, it's a complicated mix of radiation, conduction and convection, and it's definitely true that a heated floor created more conduction than a heated ceiling. In theory this can be compensated for because the ceiling can take hotter water, you're not standing on it, but as a practical matter I found it easiest to run the same water in my ceilings and floors.
What I like from a practical perspective is that ceilings don't have furnishings. The heat output of a floor is so low per square foot that things like carpets and furniture can have a measurable effect. Also, the ceiling seems to be much less likely to get damaged during construction.
Where I am, in Washington, DC, almost all new construction requires fire sprinklers. This is an issue for heated ceilings, because code doesn't allow a heating pipe within 3' of a sprinkler, they don't care that the water isn't very hot. The sprinkler heads have to be in the middle of the room so they take up a lot of the best real estate.
In a couple of rooms I didn't have enough ceiling space after the sprinklers to get as much heating as I wanted, so I put heat in the walls. The output per square foot is about midway between ceilings and floors, as one might expect. The biggest drawback is that people are screwing, pounding and drilling into walls all the time for various reason. I haven't had anyone hit a pipe yet but I worry about it.