DIYbanter - View Single Post

wrote:
Here in Michigan, it's been bitterly cold for the last couple of days.
I have an automatic thermostat which I lower the house to 65 during
the day, and back up to 69-70 at 4:30 so it's warm by the time I get
home from work.

The problem is, it took FOREVER to get back to that temp last night.
When I first came home I thought my furnace wasn't working right (had
the ignitor replaced last week), but it was running... It just wasn't
getting warm.

I change the filter regularly, but I have a lot of windows in my
house...

So the question is, is it worth it (energy wise) to lower the temp
during the day, when it takes so long to get back up to temp? I'm
thinking I'm buring as much gas to bring it back up than I might save
during the day.

With fossil fuel furnaces (as opposed to heat pumps with heat strips) you
save ANYTIME you set the thermostat back. The rate of heat loss is
proportional to the temperature differential. The cooler your house is the
slower it loses heat. As the house cools it loses less heat even if it never
reaches the setback temperature.