Lowering thermostat pays off

Dear Jim: I hear how important it is to lower my thermostat setting during winter. It seems it would just take more energy to reheat the house each morning. What is the best thermostat setting for the most savings? – Don G.

Dear Don: It actually does save energy overall if you lower the temperature setting on your central furnace thermostat. The actual amount of dollar savings depends primarily upon how low you set the thermostat and, to a lesser degree, the climate.

If you look at setback savings charts, don’t be confused by the fact that the percentage savings are actually higher in milder climates than in colder climates. This is because the total amount of energy used to keep a house comfortably warm in a cold climate is much greater than in a warm climate, making the base number larger.

It is a common myth that it takes as much energy to reheat a house as was saved during the setback period. The amount of heat a house loses is directly proportional to the difference between indoor and outdoor temperatures. Air leakage also increases with larger temperature differences.

When the indoor temperature is set lower, the indoor-to-outdoor temperature difference is smaller, so less heat is lost. If less heat is lost, your furnace has to use less gas, oil or electricity to create the heat to replace it. The amount of heat used to reheat the house, therefore, is much less than the amount saved.

The only time a setback may not be wise is if you have a heat pump with backup electric resistance heat. When it is time to reheat the house and you set the thermostat higher again, the expensive backup resistance heater may come on. If you have a heat pump, install a special setback thermostat, designed for heat pumps, which keeps the backup heat from coming on.

There is not a “best” thermostat setting for all homes and climates. The lower you set it, the greater the overall savings will be. The amount of savings per each nighttime eight-hour setback period ranges from 1 percent to 3 percent. Since many people are also gone working during the daytime, the temperature can be set lower for about 16 hours per day.

In moderate climates, let your comfort dictate how low you set the furnace temperature. As you get used to the lower temperatures and wear a sweater, you will be able to gradually lower it more. In colder climates, excessive window condensation often limits how low the indoor temperature can be set.

Use smaller room heating appliances with built-in thermostats to keep just a room or two warmer if you like. Reiker (www.buyreiker.com) makes ceiling fans with a built-in heater and remote digital thermostat.

Soleus (www.soleusair.com) makes a very efficient portable heat pump with a thermostat and remote control. Many inexpensive electric space heaters also have thermostats for zone heating.