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I am looking to retrofit a hydronic radiant heating system to the first (ground floor and basement of my house. For the first floor the plan is to install the system under the subfloor by snaking the tubing between the joists. The basement floor is slab concrete without any insulation below the slab. I don't have any ceiling height to lose so adding insulation does not seem like a good idea. Further, there is a mild moisture issue with the floor so this just seems like a bad idea.

I was thinking of running additional tubing in the ceiling. I am completely unfamiliar with the concept of radiant ceiling heating and not sure if it can be combined with radiant floor heating. Can I essentially run one set of hydronic radiant heat tubing to heat the ceiling of one room and the floor of the room above it.

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  • @isherwood I tried to clarify my question. Basically, I want to know if I run one set of hydronic radiant heat tubing to heat the ceiling of one room and the floor of the room above it.
    – StrongBad
    Apr 13 '17 at 20:03
  • I would think if you are using radiant floor heat you would have some ceiling heat already. Cable heating was big here in the Pacific northwest when power was cheep. It will work to add ceiling heat but remember heat rises so your upstairs floor heat may need to be turned down.
    – Ed Beal
    Apr 13 '17 at 22:03
  • @EdBeal Heat does not rise. Heat moves from high temperatures to cold temperatures. Hot air rises. In a subfloor/ceiling cavity, there's little room for convection, so not likely a problem there. You also don't rely on convection for a radiant ceiling, which is why they are much hotter than radiant floors.
    – Hari Ganti
    Apr 14 '17 at 21:58
  • Ok try and not insulating above a cable or radient heat system in the ceiling and see how much is in the room below.
    – Ed Beal
    Apr 16 '17 at 22:48
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You'd need custom heat spreaders, and it still won't work well

The heat spreaders used for hydronic systems only spread the heat along one face (so either a subfloor or the ceiling drywall). You would need to get a custom heat spreader for a single tube to do both.

A hydronic radiant ceiling also requires much higher temperatures than a floor does, so you'd have an uncomfortably hot floor or a rather ineffectively tepid ceiling. Neither is ideal.

You could run parallel systems between ceiling/floor joists

Two systems, with different temperatures, could be placed in parallel in the same space between joists. I can only speculate that it could work, but I've never heard of this before, so you might be venturing out a bit here.

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  • lol, I just had this crazy idea and am now considering it. @strongbad did you do it? Anyone ever heard of the parallel systems within the same joists since 4 years ago?
    – jpx
    Oct 28 at 21:27
  • I still haven't heard of this specifically, but radiant heating is fairly common for outdoor dining in California. Some places have large radiant heaters along a pergola that face downward, toward the tables. These are pretty effective, but they also operate at ~800 °C rather than conventional radiant heating temperatures. I still can't quite imagine why you'd want this, except to provide hydronic heating to a slab-on-grade storey (like a basement).
    – Hari Ganti
    Oct 30 at 5:12
  • exactly. my scenario: a retrofit where I may add radiant heat floors to main level, but it only makes economical sense if I can also use it to heat other spaces, such as my basement with uninsulated slab (hence radiant ceilings combined with staple-up for floor above)
    – jpx
    Oct 31 at 6:19
  • @jpx, if you have the headroom for it, you could look at installing on-grade insulation with PEX guides. This would raise the existing floor height by at least 1-1.5", but that may not be too much of an issue and would be a better solution. We don't do product recommendations here, but searching for "on-grade hydronic retrofit" should be useful.
    – Hari Ganti
    Nov 1 at 7:16

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