Q: All my life I have been taught to turn down the heat at night to save fuel. I have always done so, and believe it is the proper thing to do.

However, almost without exception in conversations with folks of all ages about saving fuel, I find that they deny and reject this practice. The typical line is, “It costs just as much because when you turn the heat up it takes forever to warm up the house, so it has to be using just as much fuel or more.” I seldom have succeeded in persuading such folks that this is scientifically wrong.

Could you publish an article explaining why it is always advantageous to lower the thermostat at night? Can you debunk the myth that it takes as much fuel as leaving it at a constant setting? I hope so. Many people are so stubborn on this point that they are following a wasteful practice. Someone should set them straight!

– John MacDuffie, Bernard

A: The heat required for a particular residence depends on the temperature difference between the inside of the structure and the temperature outside the structure. It has nothing to do with the heating up or cooling off of the material inside the structure. A chair cools off during the thermostat-turn-down period, and then warms again when the thermostat comes off its set-back condition. This is a wash. It has nothing to do with the energy required to heat the building. The only possible exception is this: the thermostat is located on a heavy plaster wall in a hallway which is far from a heating unit. When the thermostat comes off its set-back condition in the morning, the temperature of the building may “over-shoot” because the thermostat is late in “getting the word” that the building is warm. Almost all thermostats, however, have an “anticipatory” device to prevent this.

So the rule: “Always set the thermostat back.” The cost of electric heat is about twice the cost of oil heat. Deep 24-hour thermostat set-back on the oil thermostat is appropriate with spot electric heat where needed: while taking a shower, over the keyboard of the computer, near grandmother as she watches the kids get off the school bus, etc.

The answer was provided by Richard Hill, retired emeritus professor of engineering at the University of Maine.