It started with Xringer's innocent question:
Quote:
Originally Posted by Xringer
Maybe letting everything cool down at night, and then trying to heat it back up (fast) in the morning, isn't really that efficient.?.
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I wanted to reply there and then, but thought that maybe the answer deserves its own thread.
So, does cooling your house down and heating it back up again once or twice a day really save energy? Why? This is, of course, only during heating season.
My answer is below, but I would like someone to verify it, maybe with some numbers.
At night, or when you're not at home, the lower temperature differential between indoors and outdoors allows less heat to be lost. The longer the time with lower temperature, the less heat is lost, which makes up for any losses during warm up. The instruction manual for my programmable thermostat advises not to set it for night-day-night-day temperature changes every hour as this supposedly doesn't reduce energy usage.
Raising the temperature again allows the (gas or oil) furnace to work at close to maximum load, when it is most efficient. I'm not sure whether this is true for heat pumps electrical heating.