We will be moving to the Washington, D.C., area and expect to buy a new house. Thus, we want to compare the efficiency and costs of various residential heating and cooling systems. Natural gas and fuel-oil systems are still less expensive to buy and operate, it seems, than an electric-resistance system. How about a heat pump, which has been suggested by friends in Washington? David W. Moulton Palo Alto, Calif.
Your friends are absolutely right about the heat pump. Indeed, in that latitude, a heat pump should do an excellent job, both in heating the house in the winter and cooling it in summer.
As you undoubtedly already know, a heat pump is little more than a conventional air conditioner which can also run "backward." In running backward, it absorbs heat from the outside air and expels it indoors. Even at zero degrees F., there's still heat in the air.
"Since 'absolute zero' is -459 degrees F., it follows that there is 4.59 times as much heat still in the air at 0 degrees F., as there is between a 3 degree F., winter day and a hot, sultry 100 degrees F. summer day -- which is quite a bit, right?" says a publication by Carrier Corporation.
Still, when the temperature falls to the freezing area on the sustained basis , some supplemental heat will probably be required.
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, not warmer air coming from the heat pump.
In your area the heat pump should be sized to match the cooling load rather than the heating load.
Drop a note to the Air-Conditioning and Refrigeration Institute, 1815 North Fort Myer Drive, Arlington, VA. 22209, and ask for a free copy of the booklet, "Heat, Cool, and Save Energy With a Heat Pump." It gives some key pointers on the heat pump as well as a cost analysis for various parts of the country.