Heat pump requires care and respect

I read your answer some time ago about setting back the thermostat on a gas furnace. Does this also apply to a heat pump? If so, what range or how far back? Rick Dressell Jamul, Calif.

You should never set back the thermostat on a heat pump.

A heat pump is a very complex mechanical device and it is vital to its successful operation that it be treated with respect, says Paul B. Moore of Fedhaven, Fla., a retired engineer who has been working with heat pumps for a very long time.

"Heat-pump output is always the same at any given outdoor temperature," he asserts. "Thus, a higher thermostat setting merely means a longer running time to satisfy, not warmer air coming from the heat pump as would be the case when a furnace is turned up to a higher output firing rate."

Emphatically, it is not good practice to set back the thermostat in cold weather in an effort to save energy.

If the thermostat is set back at night, the bigger demand the next morning would be more than the fixed heat-pump capacity could deliver. You would end up calling on the less-efficient, more-costly supplemental heat source to meet the demand.

"The temperature of the air leaving a heat pump is always lower than the air leaving a furnace," adds Mr. Moore. "This fact must be understood; otherwise, the electric bills will grow."