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Heat Loss Calcutions - Cathedral Ceilings

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Member Posts: 712
Can anyone advise me on how to properly do heat loss calculations in a room with cathedral ceilings? They're not exactly walls and not exactly ceilings, since they come down to knee-walls that are 55" high.

For radiant floor calculations, how to I account for the flooring covered by dresser and chest, as well as flooring covered by a king size bed and sofa? It seems that the calculators just ask you the flooring material (oak on plywood underlayment with Onix staple-up).

Thanks
Steve from Denver, CO

• Member Posts: 2,398
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Ceilings, Schmeilings....

I had a discussion years ago with a pedantic architect who grilled me on whether I considered the inside wall of a mansard roof a wall or a roof.... sheesh. Like it matters what you call it; it still loses heat at a given rate per degree difference....

Call it something and calculate it as a separate entity if you must. Remember, each surface be it wall, roof or floor, may have different R/u values and even different delta-T's. Take each as a line item and keep going. This means the broad slope of a cathedral ceiling too.

Remember your framing percentage and apportion your "at framing" and "between framing" factors. Be realistic.

Remember too that knee walls are seldom sealed on the exterior side. How many times have you been in knee-wall voids and seen bare insulation exposed to a vented eave space? Cathedral ceilings with over-venting for that matter.

Naturally sealing that outer surface in plywood or drywall makes sense but absent that, the air-stopping power of fiberglass batts in those conditions is about as good as it's ability to stop Gamma radiation.

Point being, take the conditions into account, each as they are.

For the radiant question, I ignore fixed items such as islands but furniture with about 4 inches of gap or more underneath, I do not think more about it. If it is a bureau or something tight to the floor (movable, granted), it cannot amount to much in the big picture. Tube it of course but see if you could live without 12 SF of radiant surface. Again, if there is a gap underneath where air can circulate, I would not worry about it.

Plus, you will always know where to find the cat.