Quote:
Originally Posted by Mikesolar
So, MN, what is your target heat loss?
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Current manual J calculates to just above 26000 but my actual heat loss is just under 18000 at 70f and -13 outside(83 degree difference). ..although I never keep it at 70f when it is that cold outside and I'm comfortable colder than that normally anyway.
Here are my figures
Walls R13 fiberglass+R5 polyiso+R20 XPS=R38(maybe a point or two less because of bridging but in reality its very small when it is behind R25 of foam).
R38 walls 4596
R60 roof 1494 (I'm actually planning for more but these are the figured I sketched into notepad)
R5 glass 3602
9692 BTUhr at 83 degree difference
116.8 BTUhr per F
Add some for slab losses and air infiltration but since I'm well below the heat loss for manual J in regards to my actual measurements, I have a feeling that I could be below 10,000BTUhr either way. The odd thing is that my house configured this way with a 60 degree difference inside versus outside would probably hit the passive heat load figure which would be 70 inside and 10 outside or 60 inside with 0 outside. If I keep natural gas heat, I can use aggressive setbacks with a quick return to warmth. With my current 57,000 BTUhr output furance I can go from 40 degrees to 70 degrees in under 3 hours. I don't normally keep that large of a setback and if I stick with natural gas, the next furnace will be a 40,000 BTUhr condensing furnace. With better insulation I wouldn't sink as low into the setback, although recovery would be a similar time. When the house has warm air flowing, it feels a good 10 degrees warmer inside and once the furnace is running for a good 15 minutes, even 50 degrees feels acceptable with 55 comfortable with a t-shirt, subtract 5 degrees with a hoodie.