As the costs of oil, natural gas and electricity to fuel conventional heating and cooling systems rise, homeowners are increasingly installing heat pumps. By extracting warmth and coolness from the outside air or ground, heat pumps can provide greater efficiency and lower cost over the long haul.

Two basic options predominate. In air-to-air designs, a unit outside the house relies on air as a source of heat or a place to dump heat. In ground-based designs, fluid in tubes laid in the ground provides the heat transfer. In each case, a refrigerant travels in pipes from outdoors to an inside unit, and a blower sends the resulting warmed or cooled air through ductwork into various rooms. The systems are often likened to a reversible air conditioner that can stream cool air or exhaust warm air throughout the home. “When the season changes, you just flip a switch and the flow reverses,” says Leo Udee, account manager at Alliant Energy in Madison, Wis.

Even though both systems require electricity, they can attain greater efficiency than conventional designs because instead of consuming fuel to generate warmth or coolness from scratch they exploit heat or cold already present in the outside air or ground. Air-to-air systems are most effective when outdoor air is above 32 to 35 degrees Fahrenheit, however, so they are prevalent in the milder regions of the U.S. A small conventional heater can be added in colder climates, but that drives up cost. Ground-based systems with tubes installed six to eight feet below grade are useful in wider areas because the temperature of the earth does not dip below freezing at that depth, although they generally cost more to install.

Heat pumps have been around since the 1950s and have become more competitive in recent years because “the motors and compressors have gotten more efficient and cost less to operate,” says Randy Scott, vice president of product systems management at Trane in Tyler, Tex. “And the condensers and evaporators can transfer more heat even as they have become smaller.”

Heat pumps still command only a modest proportion of the home heating and air-conditioning market. Even so, both styles are seeing strong growth, especially for retrofits. So many homes were built in the 1970s, 1980s and 1990s, Scott says: “Their systems are nearing the end of their lifetimes.”

Note: This article was originally printed with the title, "Warming and Cooling".