Well, let's say it's really cold outside, so you're running your
heater. Maybe you normally set your thermostat to 72 degrees. If you
turn the thermostat down to only 70 degrees, then the heater won't have
to run as much, for two reasons. It doesn't have to get the house as
hot in the first place, and it has to work less hard to replace all the
heat energy which is lost to the outside. This second effect is the
most important, particularly if the house is not insulated well. The
rate at which heat is lost is proportional to the difference between
the temperature of the house and the temperature outside, and how much
the heater runs is therefore also proportional to this difference. The
less the heater runs, the less energy it uses.
On the other
hand, let's say it's really hot outside, so you're running your air
conditioner. In this case, if you turn your thermostat from 72 degrees
to 70, your air conditioner will have to run more in order to make your
house that much cooler. Since the air conditioner is running more, it
will use up even more energy.
So in sum, if you're running the
heater and you turn down the temperature on your thermostat, you will
save energy. But if you do the same thing while running the air
conditioner, you will not. If the temperature outside is the same as
the temperature you would like inside, then neither your heater nor
your air conditioner needs to run.
For more information on how thermostats work, check out the answer to the question
Thermostats.
-Tamara and Tom
(published on 10/22/2007)
