Quote:
Originally Posted by TimJFowler
Calculating therms (or kWh) used per heating degree day for the same billing period before and after the insulation / weatherization project (i.e. December '09 and '10) will give you a good basis for comparison. This assumes that your other gas or electricity uses are comparable, but it is much better than nothing.
That said, an 18% reduction in energy use is quite respectable! And with an increase in natural gas prices means you save even more $.
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It's really hard to say that the insulation is entirely the result in savings like that.
As an example last december/january I used 3171 kwh over 62 days and the HDD was 956.5 giving me a kwh/hdd of 3.315 I added R40 to the attic after that. This year my december/january period I used 2567 over 62 days and the HDD was 1005.5 giving me a kwh/hdd of 2.553 or a 23% decrease in energy use for the given temperature.
Sounds great but it does not take the fact that I'm smarter about the heatpump and use it more efficiently namely I always have the woodstove going on ultra cold days where the heat pump kicks the backup heater on.
I'm sure moving from R12 to R52 in the attic helped a bunch though.
<edit> HDD is calculated at 18.5C in my case since that's the coldest I let the house get with the baby </edit>