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kwired:
My home built in 65-66 has full fiberglass insulation in 2x4 studs, and 10" in the second floor ceiling, and a furnace with possibly 70% efficiency. During the summer I did a thermal time constant estimate, and it seemed to be a little less than 24 hours.
During the summer my gas consumption is about 1 CCF or 100,000 BTU per day, hot water heating and some range top cooking.
Last month gas consumption per day was:
1-7-2014, ........ -5 F outside, ...... 70 F inside, ...... in-out diff 75 F, ..... 25 CCF ..... 0.3 CCF/F
1-13-2014, ...... 40 F outside, ...... 70 F inside, ...... in-out diff 30 F, ....... 9 CCF ..... 0.3 CCF/F
1-21-23-2014, ... 0 F outside, ..... 70 F inside, ...... in-out diff 70 F, ...... 20 CCF ..... 0.29 CCF/F
If I could reduce this heat loss by a factor of 5, then it might be possible to increase the thermal time constant toward 4 days. In my case not possible without rebuilding the house.
There are architects in town that are pushing very thermally efficient home designs. Usually 6" walls with staggered 2x4 studs with foamed in place foam insulation, and staggered 2x4 studs. Basements with insulated walls and floors. Ventilation heat exchangers. And ground based heat pumps. But at our present natural gas prices I think a high efficiency gas furnace is operationally competitive with ground based heat pumps, and a lot lower capital cost.
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