cy (cychan) wrote,
cy
cychan

Turning the heat down vs. Leaving the heat on

It's apparently a common misconception that leaving the heat on at home while you're out takes less energy than turning it off (or lowering the temp) and then heating it back up later. This idea probably stems from the large amount of energy necessary to bring a cold house up to a comfortable temperature (a high "peak load"), but it ignores the energy being wasted while you're away (a high "average load").

An easier way to determine the total amount of energy being used in either scenario is to consider the rate at which heat leaves your house. The total amount of heat that leaves your house is equivalent to the amount of heat your heater has to produce to maintain a set temperature. So the goal is to minimize heat loss. According to Newton, the rate of heat loss is proportional to the temperature difference between the house and the outside. In other words: the warmer the house, the higher the heat loss. The figure below (linked from this blog post, thanks Patricia!) helps to illustrate how much energy would be saved by turning down the thermostat at night.

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