Rhonemas said:
Efficient houses have progressed in this way.
First, there was the regular 2x4 walls with 3.5" insulation between them.
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Of course, this is unscientific, but my experience. My current and former homes have 2x4 walls and 3.5". The walls never seemed to lose much heat until a certain threshold - like below 25 degrees....
My new house here is quite tight and yet still a lot of windows. Probably insulated to whatever the min. code are in Ma - but it really holds heat well - again, until the temps get down in the teens or below...
So although the formulas might be linear, it seems there is a comfort factor or something else that is when the side walls actually seem to radiate cold.
I always assumed that they insulated floors well to keep your feet warm, but that doesn't really make sense since there is usually no heat at that level anyway - in fact, I removed the floor insulation in my former house and the floor was actually warmer due to heat loss from the older boilers I had in the basement!
It's all relative - I remember some super-insulated houses built in 1979 which I toured that had passive solar and other such features - firing up the wood stove for a couple hours (they had tons of masonry mass near the stove) kept the place warm with only a couple degrees drop in fairly cold weather...
BUT, there is a big difference between southern jersey cold weather and VT cold weather...
There is always a point of overdoing it, since you need air changes and such things in a house. But the moral of this thread is something we rarely think about - That a 2800 sq ft house (like mine) in the same location might need only 20,000 BTU per hour average in the coldest weather or might need 100,000 BTU or more....the only difference being the insulation, orientation and other such factors. This should be proof of the value of conservation, when you can get 5 or 6x as much out of the same fuel.