1. Regular Guest
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Apr 2005
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Hello:

I'm a curious home owner seeking any input or advice on the following. In particular, I have two questions regarding how loads are calculated in light of my townhome's "shared exterior walls" and a large vaulted ceiling in the upstairs master bedroom.

The house is a middle unit that shares its side walls with two neighboring homes, one shared wall on the north side and another shared wall on the south side. Are these "shared exterior walls" even considered as exterior walls in the load calculation? How much heat loss/gain is coming through these walls?

Lastly, how do vaulted ceilings affect heat gain/heat loss? How do vaulted ceilings compare to normal leveled ceilings in heat gain/loss? How do you calculate such gains/losses for these ceilings?

Thanks. Much appreciated.

2. The shared walls aren't looked at. The vaulted ceiling would add some wall space to the front & back plus you calculate ceiling load. Most townhomes like yours, inside, have very low loads and are often way oversized we find.

3. Regular Guest
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Mar 2004
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Indeed. Walls only count as walls for heat loss or heat gain if they are exterior walls. While the walls between units are important and official, they're still not exterior, so they count for 0 heat loss and 0 heat gain.

My condo is townhouse-style in construction, with common east and west walls and heavy tree cover on and over the south side. It's two stories, built in '81, in Atlanta, and about 1700 square feet. Per HVAC-Calc, my heat gain, despite just average insulation and windows, was about 20,000 BTU. Heat loss is 33,000 BTU. I wanted a top of the line furnace but needed 80% because of the risk of condensate freezing in my attic, and frankly had a hard time finding anything small enough.

Vaulted ceilings? Well, you put in the average ceiling height for the room, and it knows the difference between a hot attic over insulation and a hot roof over the same amount of insulation. The challenge is knowing how much insulation is in the vaulted areas, because they're not accessible.

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