Quote:
Originally Posted by MoneyGuy
We recently installed a Nest system so technically this is home-improvement related.
My wife says that turning the thermostat down actually costs us money as the furnace runs more to heat a cold house but I contend that the furnace runs less. We keep it at 21C when my wife is home and I have no problem turning it down to 18 at night or if she's out for a few hours.
I think I read that it's efficient to turn a thermostat down one degree for each hour of away time. Has anyone seen definitive evidence whether this is correct?
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If your wife was correct, it would take the same amount of energy to keep your house at 15C or at 35C inside. How much energy is required to maintain a temperature is a product of the surface area, the insulation value, and the temperature differential. Turning down the heat for a number of hours decreases the temperature differential, therefore reducing the energy required to maintain the temperature over that time period.
Yes, the furnace runs longer when it has to rewarm the house, but that is offset by the time where the furnace doesn't have to run during the cooling off period.