Radiant Heat in Walls

Discussion in 'HVAC Heating & Cooling' started by seaneys, Nov 23, 2007.

  1. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Hello,

    I'm thinking about running a few loop of radiant heat into the walls while I put in the underfloor radiant heat. It might be nice to have around that bath / shower.

    Has anyone done this before? Can you think of any downsides? I figure I'll pull it from the manifold so that I can balance it later.

    Steve
  2. frenchie

    frenchie Jack of all trades

  3. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    It is nice for showers; particularly tile or some sort of rock. I planned to do this but rather stupidly forgot about it when the tubing was installed.
  4. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    If it is an outside wall then the disadvantage in these days of $3 fuel oil is that you are putting a heat source inside a wall where a large fraction of the heat is going to warm the outdoors.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,843
    Location:
    Cave Creek, Arizona
    walls

    The other disadvantage is that you have to be very careful when you drive hangers to hang pictures or towel bars. In the ceiling is more forgiving and less apt to happen.
  6. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    Bob - yes it needs insulation. I put in 6" of urethane foam. Just forgot the tubes. And if you put tubes in places you should take pictures (preferably with some visible measuring benchmark) so you will know where to put nails.
  7. Rancher

    Rancher Guest

    I remember looking to buy a home, and some homes built in the late 70's had radiant heat (electric) put in the ceiling, you were supposed to call the builder if you want to put a hook in for a hanging plant or anything else into the ceiling. They were also not very efficient, heat rises, does a poor job at heating a room.

    Rancher
  8. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    Actually I believe the ceiling is a great place for radiant. Radiant heat does not rise; it radiates (line-of-sight). Refering to "regular" heat, it rises because of air convection. Air is the transfer mechanism of the system. The infra-red from a radiant system warms the people and objects. There is an ancillary air temp rise from the heated objects.

    As opposed to in-floor, it has no problems with furniture generated heating shadows, and the rugs that she who must obey insists have to be in the room. It is harder to install, but it works well.
  9. Rancher

    Rancher Guest

    I should have said I never bought one of those houses, but that was just the word on the street about their problems.

    Also the radiant cable is above the sheet rock in the ceiling, at least it was here, so it radiates down thru the sheet rock and up thru the R-19 in the ceiling. Hydronic in the slab works so much better, I was talked out of putting the slab on Styrofoam, but did insulate 4" b/t the slab and stem wall. Next house will be floating on Styrofoam, I don't care how much the concrete sub doesn't like to do that...:D

    Rancher
  10. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    Yep rancher - had the same argument about slab insulation. I could also not seem to get them to do the vapor barrier properly. It is there but not pverlapped and sealed at the seams. Didn't see that until I had them remove some foam to put it under the footers like I told them to do. And then it was too late. Someone lese visiting my site said they had just done a naked slab except for 1/2" of foam under the last foot or two of the slab edge. That was what their contractors had told them was enough.

    In a lot of places you should probably do more than R19 in the attic. It is cheap to put in fluffy stuff. My approach was to foam a layer to air seal than put about 1.5' of blown stuff. There were installation issues with foam. If I had to do it over I would consider insulating the roof deck instead. Of course that creates other things you have to do.
  11. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Hello,

    I'm strictly thinking about this as a way to augment the radiant that is stapled up from the basement ceiling.

    The heat load sizing indicates that I might need a little supplemental heat on extremely cold days. My thought was to try to supplement a small amount by adding heat to the interior walls. One nice benefit of this is that these walls include the walls adjacent to the tub and shower.

    I've read that radiant in the walls can inhibit mold / mildew. Does anyone know the logic? I can find this in advertisements, but do not see a decent reference.

    Steve
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,156
    Location:
    New England
    Raising the temperature of the inside of a wall also increases the dew point, so the potential water vapor intrusion isn't as likely to condense. Vapor is relatively harmless, liquid is a problem.
  13. leejosepho

    leejosepho DIY scratch-pad engineer

    The amount of insulation necessary is somewhat relative to the size of the slab and how much mass is wanted or being used for storage of heat. A vertical barrier of insulation around the perimeter is always important, but heat will only radiate about four or five feet deep. Hence, and with cost-efficiency in mind, large slabs are seldom insulated other than around the edges.

    Attached Files:

  14. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    I agree the edges are the most important, and more so the colder the climate and the closer to the surface. And the payback should be analyzed to make a reasoned choice. The earth from what I have seen a particularly effective heat storage system on this sort of scale. By limiting thermal mass to the slab, it provides better response times. Overall insulation levels also help not only in reducing overall energy cost but it lowers the required rate of delivery of energy; hence smaller boiler and heating components.

    My cut on this house was a relatively small amount for foam vs a lot of years with increasingly expensive fuel. I made those choices in many aspects of the house. With the oil economy where it is, it is increasingly difficult to generate decent ROI numbers when energy costs are involved. My house is "excessively insulated" according to a whole bunch of contractors and vendors around here. The window vendor kept trying to convince me that I should not buy my windows because it was not cold enough here. Since this sort of insulation is mostly a one time shot, I chose to gamble on the insulation side rather than fuel. It was a chooce I made. YMMV
    Last edited: Nov 26, 2007
  15. "enough" and "plenty" is rule of thumb based on experience. Often far too little when you recalculate using different numbers.

    In some climates the buildings all feel cold in winter. Poorly insulated.
    In other climates the buildings all feel warm in winter. Well insulated, in a colder climate.

    paradox. In a cold climate the occupants have warm floors walls and ceilings. They spend less too. They have warmth comfort and cost savings.

    david
  16. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Is it reasonably possible for me to retrofit the ceiling later if I need additional heat or decide I'd like to try it? I'm pretty much buried now. I'd like to defer the work if needed.

    I plan to add radiant in the interior walls....

    Thanks,
    Steve
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