Hey Mr. Green,
I have oil heat. I am gone about 12 hours a day. Should I turn down the heat when I leave, and by how much? Some people tell me that it takes more oil to reheat the walls, etc. than to leave it at a constant temperature all the time. --Jeff, Hellam, Pennsylvania
Your advisors are wrong. It takes more energy to maintain a constant temperature in a house than to turn the temperature down when you go out or go to bed and then reheat. Our ancestors observed this truth long ago, which explains why they didn't waste precious firewood by constantly piling more logs on the fire all night long in their caves, cabins, or hovels. It is a basic thermodynamic law that heat moves to where it is colder. So if your heat is always turned up, there is a constant transfer of that higher heat from the inside to the outside, even in a well insulated building. Hence, maintaining a higher temperature when you’re not inside is, in effect, heating the great outdoors.
The truth of this could be demonstrated with equations involving heat transfer and conductivity, and assorted coefficients for various materials, but an easier way to grasp the basic principle is to think of yourself as a furnace. Thanks the fact that you’re a warm-blooded creature, your body constantly burns fuel to maintain a temperature of 98.6 degrees. When you jump into a cold bed, your body heat can warm you up fairly quickly, getting you to the same comfort level you’d feel if you’d been lolling there burning up energy all day long. It doesn’t take long for the heat you’re producing to match the amount that is escaping. (The same basic principles apply to water heaters: a tank heater that hold water at a constant temperature uses about 25 percent more energy than an on-demand water heater that only heats the water while it’s being used.)
So turn the thermostat down to 55 degrees when you’re not home or asleep, and you can save anywhere from 5 to 20 percent on your heating bills, depending on insulation, windows, etc. Also keep the temperature at a 68 degrees max, which is comfortable for most people, and if it’s not, do as Jimmy Carter wisely recommended long ago, and put on a sweater.
If you’re the type of person who forgets to turn the thermostat down, you should consider a programmable thermostat that does this automatically at times you choose.
Finally, remember that the dead of winter is also the rebirth of light, so may all you environmentally curious folks who are kind enough to read me in print and here online enjoy a splendid holiday season and a Happy New Year. Keep those questions coming, and do not be discouraged by the recent election of all those environmentally unfriendly, climate-change-denying, tree-hugger-hating politicians. Put the pressure on them however you can, and if you’re one of those people who spends an average of 23 hours a month on Facebook, turn off the computer, sally forth to your nearest environmental group, and become a real-life activist.