Dear Jim: Our church installed a geothermal heat pump. The contractor told me they are also the most efficient, comfortable way to air-condition and heat homes. Would one be a good choice for my 2,000-square-foot home? – Kyle N.

Dear Kyle: The U.S. Environmental Protection Agency analyzed six major cities of different climates, from Burlington, Vt., to Phoenix and found geothermal heat pumps produce the lowest year-round utility bills. Other advantages are their durability, low maintenance and quiet operation.

To give you an idea of how efficient they are, an older, but still working, central air conditioner may have an efficiency rating of 8. The most efficient geothermal heat pumps have efficiencies as high as 27. If it now costs you $300 per month to cool your house, your monthly cooling electric bills would be cut to about $90. There also would be winter savings.

Every geothermal heat pump offers an optional desuperheater. During summer, this diverts heat drawn from inside your house to your water heater. With a large family, this can save another $100 per month for water heating. During the winter, some models also are designed to heat water efficiently.

Geothermal heat pumps are so efficient because they use the huge thermal mass of the Earth to cool your home during summer and to heat it during winter. Even though the outdoor air may vary from subzero to 95 degrees year-round, the ground temperature ranges from only about 45 to 75 degrees.

The cost of installing a typical 3-ton (36,000 Btu) geothermal heat pump will cost several thousand dollars more than installing a gas furnace and a central air conditioner. The geothermal heat pump often will pay back the higher initial cost in about eight years or less depending on local utility rates. Geothermal heat pumps typically have a life of 20 years or more.

Many geothermal heat pumps offer all the comfort options similar to standard air conditioners or heat pumps. Models are available with two-stage compressors and efficient variable-speed blowers to closely control temperature and humidity. Some models use ozone-friendly R410A instead of freon.

There are two designs of geothermal heat pumps. One type uses a polyethylene pipe ground loop either in a horizontal trench or vertical holes in your yard. A water-antifreeze solution runs through the pipes, which are connected to the unit inside your home. No outdoor unit, with a noisy condenser fan or coils, is required. The indoor compressor makes little sound.

The other design, called DX, uses small copper tubes buried in the ground and the refrigerant flows through them. With this direct heat exchanging with the ground, less tubing is needed. This is often ideal for small lots.

Write for (instantly download – www.dulley.com) Update Bulletin No. 924 – buyer’s guide of 14 geothermal heat pump manufacturers (26 models) listing stages, efficiencies, outputs, features, freon-R410A, cost comparison chart, and ground loop details. Include $3 and a business-size SASE, and send to James Dulley, 6906 Royalgreen Drive, Cincinnati, OH 45244.