Q  We’ve always used a setback thermostat to lower the temperature at night and during the day while we’re gone. My son-in-law says we’re not saving anything, claiming the amount of energy used to reheat the house is far greater than if we left the thermostat set at a constant temperature. Who’s right?

A  You’re right. Your son-in-law holds a common misconception, which has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building temperature drops to the lower setting. You save fuel between the time that the temperature stabilizes at the lower level and the next time the heat is needed. So, the longer your house remains at the lower temperature, the more energy you save.

Studies show you can cut costs by as much as 20 percent by lowering your thermostat 5 degrees F at night and 10 degrees during the day when no one is Home. The same goes for raising the temperatures by that same amount when using air conditioning in warmer climates.

However, if you have a heat pump without a setback thermostat that’s designed for heat pumps, you won’t save money in this scenario because it causes the heat pump to operate inefficiently, which cancels the savings.