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Radiant ceiling covering info

EricAune Member Posts: 432
I'm looking for more info on radiant ceiling covering guidelines. I've got a radiant ceiling that we roughed in this winter on a vacation property here in MN where the architect and interior designer have decided to change from standard sheetrock to 1" straight-sawn Douglas Fir. The area is small, 8'x15 with one loop in it and doesn't actually figure into the panel design but is piped to the manifold with the rest of the ceiling in an attempt to condition the immediate area due to a decent amount of glass on the wall below. I'll refer to this ceiling as the "shed roof", its slightly less that a 4/12 pitch and rests on an exterior wall, rising to a open loft area above

In Siegenthaler's 'Modern Hydronic Heating' [2nd edition] he lists surface temp guidelines for gypsum at 8'-10' to be 100F-110F. This is how I have designed all the ceilings I have installed over the last decade and I have had success with at least two dozen of them but all have had typical sheetrock covering. Maybe I'm over thinking this, I know the surface temp of this panel is designed at 109F with a 160F supply temp on the manifold for the entire ceiling.

I'm questioning the surface temp as it relates to the wood. I'm less concerned about the Rv of the wood, the output per sq ft of the shed roof will be approximately 60 Btu/sqft. What are your thoughts? Should I just stick to the surface temp guidelines for a wood floor?

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  • Tinman
    Tinman Member Posts: 2,808
    IMO, yes. The wood doesn't care if its installed on a floor or inverted on a ceiling, nor will the wood characteristics change from one to the other.
    Steve Minnich
  • dscottmilner
    dscottmilner Member Posts: 5
    I would be very interested in your running costs.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    I guess the question is, what IS the maximum allowable wood surface temperature. To the best of my knowledge, so long as no glues are involved, then it is limited to the woods flash point... I mentioned glue thinking of plywood, which can fail from too high a temp due to glue failure.

    But stop and think about dark colored shingles on 5/8" plywood. What temperature do you think THAT wood would get to...

    The R value of the wood dictates supply water temperatures required to achieve the value per square foot you are looking for. That and the construction detail between the tube and the final emitting surface.

    Radiant ceilings don't put out the same btut/sq ft/her that floors do because you are missing the contribution of convective energy.

    A floor delivers 2 btus per sq ft per degree F difference between surface and air. Ceilings deliver almost half as much. So 60 plus 65 = 125 degree F wood temperature.

    Knowing the total R value between the plates and the room side of the wood will be necessary to determine required water temperature.

    I am sure the wood can handle 125 f surface temps but you will want to make sure they use kiln dry wood, and maintain rH in the space between 30 and 60% or expect cracking and checking of the wood.

    Contractual caveats...


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