Before deciding for or against a heat pump, here are some things you should know:

Types. The more common central units (either single-package or split between an outside compressor and an inside air handler) can heat and cool a whole house. Room units - designed for window, through-the-wall and free-standing installation - discharge warm or cool air directly into one or two rooms.

Insulation. There is no chance that a heat pump will operate correctly or economically in a poorly insulated building. PEPCO and VEPCO can provide information and recommended insualtion standards.

Quality equipment. A well-engineered heat pumpis a complex mechanism. Steer away from the bottom of any manufacturer's line and from "builders" equipment." NBS studies shwo that high quality units more than compensate in reliability for their higher initial cost.

Authorized dealer. It pays to buy from an authorized dealer with a reputation for skilled mechanics.Ask around: Good installation will minimize inconvenient repairs during the full warranty period (usually one year on parts/labor; five years on the compressor) and costly repairs later.

Service contract. At warrantly expiration, it is wise to consider a service contract as part of normal operating costs. A compressor's life expectancy at present is less than 10 years, and repladement will cost a minimum of $300. Most service contracts provide for preventive maintenance twice yearly.

Control modifications. A variety of indoor an outdoor thermostats and other control devices is available to modify heat pump performance according to individual preferences. Some are geared to economy of operation: to enable manual control of resistance heaters, for example,or perhaps simply to prevent them from coming on to give a quick response when a thermostat setting is raised.

Ductwork. Don't plan to scrimp on ductwork. A heat pump delivers air at 100 F instead of at 130-160 F as combustion furnaces do. At lower delivery temperatures comfort requires that more air be circulated. Unpleasant drafty effects can result if ducts are not carefully planned and installed.

Closing off rooms. Don't plan to economize by shutting off the heat in more than one unused room at a time. Any significant reduction in air flow could damage the compressor.

Potential. Unlike gas-and oil-fired furnaces, the heat pump is not dependent on a single scare resource. Electricity can be, and increasingly is, generated from resources that are nonfossil (nuclear, hydro, solar) or, if fossil, plentiful (coal).

Energy efficiency. The Air-Conditioning and Refrigeraiton Institute publishes a certified unitary heat pump directory that lists the capacity of different units and the power input they require for both heating and cooling. The ratio of capacity in Btu's to power input in watts is known as the Energy Efficiency Ratio. The higher the EER, the more efficient the heat pump. (Send $1 to ARI, 1815 N. Fort Meyer Dr., Arlington, Va. 22209.)

Heat pump display. PEPCO has a display of different types of heat pumps in its lobby at 1900 Pennsylvania Ave. NW.