|Does it make sense to raise the thermostat setting on your air conditioner when you leave your house, since when you come back, you have to lower it again and the unit has to work more? Are there any energy savings? — AN, Herndon, VA
You will save energy and money by raising the thermostat setting when you leave your home and then lower it again when you return. That's because the rate at which heat flows into your home from outside is roughly proportional to the difference between the indoor and outdoor temperatures. By letting the indoor temperature rise, you slow the heat flow into your home. With less heat flowing into your home, the air conditioner doesn't have to pump as much heat outside and that saves energy. Moreover, an air conditioner is more energy efficient when the indoor temperature is closer to the outdoor temperature, so letting the indoor air warm up saves even more energy. While the air conditioner does have to work steadily for a while when you return to your home, its efficiency is still good during that time and the energy saved while you were away more than makes up for the energy consumed when you return.