Using heat pump at best efficiency

I have just moved into a house with a heat pump and would like to know the most efficient way of operating it. According to a friend, one should set the temperature at the desired point and then leave it there night and day. Yet I feel I do not need nearly so much heat at night. Also, if I close the floor vents in several unused bedrooms and shut the doors to them, won't I be saving heat that would go into these rooms? What is the "resistance heat" that is referred to when you raise the thermostat high enough to turn on the heat again? Mary E. Smith Madison, Va.

Heat pumps are very complex mechanical devices and it is essential to their successful operation that they be treated with respect, according to Paul B. Moore of Fedhaven, Fla., a retired engineer and inventor who has been involved with heat pumps for a very long time.

Your friend is entirely right. Set the thermostat at the temperature you want to maintain in the house and then leave it there day and night, Mr. Moore advises.

Heat-pump output is always the same at any given outdoor temperature. Thus, a higher thermostat setting merely means a longer running time to satisfy the demand, 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.

Also, a heat pump is never supposed to handle the heating demand without the help of suplementary resistance (electric) heat.

If you cut back the temperature at night, the demand for heat the next morning -- when the thermostat is returned to its normal daytime setting -- will be so high that the heat pump will call on the less-efficient, and certainly more costly, supplemental heat source. As a result, you will use more energy, not less.

Another thing: Heat pumps are very responsive to changes in air quantities, not only because of the impact on capacity but also because the reduced air quantity will raise the compressor heat pressure and could cause failure, Mr. Moore warns.

This is the reason it is not good heat-pump practice to close air outlets or return registers or to close off rooms, if these change the air flow at all from what the heat pump's design calls for.

Likewise, it is important that the air filter be kept clean at all times so as to maintain the designed air flow.

There is no way to calculate if power can be saved by closing off a room, or rooms, but it is safe to predict trouble if such tactics reduce the air flow. If a house is very large, it might be wise to zone it and install more than one heat pump; thus, one zone could be shut off entirely while not affecting another zone.

Usually, when rooms are closed off to save heat, the greater heat discharge through the colder walls of the closed-off areas eats up the savings by demanding longer operating cycles to satisfy the thermostat settings.

Remember, "the temperature of the air leaving a heat pump is always lower than the air leaving a furnace," Mr. Moore concludes. "This fact must be understood; otherwise, your electric bill may get a lot bigger."