> I've heard that you should not have them drop more than 10 degrees and
> only if you are going to be dropped for more than 8 hours because
> you waste
> so much energy bringing the temp back up.
Oddly enough, my high school physics teacher asked me that very question
almost 40 years ago (although in relation to refrigeration rather than
heating). It does not "waste" energy to bring the temperature back up,
unless there is something very wrong with your furnace. In fact, the
furnace is MORE efficient running all the time, with colder intake air.
So the answer to your question is to always reduce the heat just as much as
you can stand. If you're only going to be out of the house for 4 hours, so
what ? Spin that dial down to 40F (or whatever keeps your pipes, plants &
pets from freezing).
The heat lost from the house is primarily a function of the inside temp, and
the outside temp. The lower the inside temp, the less heat lost. And less
heat lost means less energy bought.
My folks' house is only a bit over 100 years old, but they had great results
by covering the inside of the walls with styrofoam/foil board. The payback
was almost immediate, as they had to have a new furnace anyway and the extra
insulation kept them from having to buy two of them.
Randall
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