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spray foam and radiant

drhvac Member Posts: 190
I have a house where the rooms above the garage are much more draftier than the other rooms. I want to take down the ceiling and have it all spray foamed to insulate it much better, and seal up all the drafts. If I do that, I would like to put radiant heat under the floor. What is the best way to install the pipe under the floor, and is it ok to spray foam over the pipe once it is installed? I heard of installing the tubing, and than insulating with the foil side up to reflect the heat upward, but never heard of anyone spray foaming over the tubing. The floor above the radiant has hardwood flooring with carpet over it.

Thanks in advance


  • Gordy
    Gordy Member Posts: 9,537
    Floor warming

    Or main source of heat is the radiant going to be for. You should use extruded plates in any case unless using a suspended tube detail which uses higher water temps.  Keep a 2" air gap in either method with xps then foam it.

      Foaming or insulating tight against the tubing halts the convective benefit. You also run the risk of the spray foam expanding between the tubing, and the sub floor if you spray foam right against the tubing not so much of a worry if you have plates. At any rate you should still have the 2" air gap.  Pay close attention to good insulation detail at the rim joist area.
  • drhvac
    drhvac Member Posts: 190

    Makes sense that the spray foam could get between the tubing and floor. What is xps? And your right, around the perimeter is where most of the drafts come from. Maybe foam along the outside, then a rigid type insulation foil side up would be a better way. what kind of water temp. do you estimated will be needed to go through hardwoodflooring and carpet?
  • Gordan
    Gordan Member Posts: 891
    Depends on those devilish details

    Even among extruded plates output varies. Then, you have to take into account the R-value of anything on top of the subfloor. One key question that you don't seem to have answered: will this be the only (or primary) source of heat? If not, it's unlikely that the floors would get particularly warm before the room begins to overheat.

    Go to www.radiantengineering.com or look up the Uponor Joist Trak installation guide for some output charts with different top-side R-values.
  • drhvac
    drhvac Member Posts: 190
    it would be the primary

    source of heat in that zone. The other two zones are baseboard. I don't get what you mean that the room would over heat.. Are you saying that it would take a long time for the floors to get warm, and once it does, it would overshoot the t-stat?
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    he's saying

    if you don't have much load to meet with the radiant, the floor would provide all the heat you needed before it felt warm... output for a floor is roughly 2 btus/sqft per degree over room temp, so a 70 degree room with a 75 degree floor will put out about 10 btus/sq ft.... and that will feel cool to the touch.

    so if you had other heat in the space, there isn't much for the radiant to do. there are ways around that but ideally the radiant will meet the load by itself.

    a heat load calculation for this space should really be done.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • drhvac
    drhvac Member Posts: 190
    heat load

    I am going to do a heat load and get back to you. As of now, the space i am proposing to heat with radiant above the garage is being heated by baseboard. I would like to take the baseboard out and replace it with radiant. As I mentioned earlier, I was planning on taking the ceiling down in the garage because there is hardly any insulation above the ceiling, and it is very drafty above. So with the ceiling down, that would be the time to put the radiant in. I should mention it is a double garage, and there is a utility room behind it that would be part of the radiant zone. The area is approx. 865 sq. ft.

    thanks again for your help.
  • Gordy
    Gordy Member Posts: 9,537
    R value of existing floor coverings

    need be considered as already mentioned. If you use the link provided as you can see by the thermo fin c output chart there is a big difference when you go from an r1 to an r2 floor covering.

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