The biggest benefit of GHP's is that they use 20 to 50 percent less electricity than conventional heating or cooling systems. This translates into a GHP using one unit of electricity to move three units of heat from the earth.

According to a report by Oak Ridge National Laboratory, statistically valid findings show that the 4,003-unit GHP retrofit project at Fort Polk, LA, will save 25.8 million kilowatt-hours (kWh) in a typical year, or 32.5 percent of pre-retrofit whole-community electrical consumption. This translates to an average annual savings of 6,445 kWh per housing unit. In addition, 100 percent of the whole-community natural gas previously used for space conditioning and water heating (260,000 therms) will be saved.

In housing units that were all-electric in the pre-retrofit period, the GHP's were found to save about 42 percent of the pre-retrofit electrical consumption for heating, cooling, and water heating.

Unlike any other heating and cooling system, a geothermal heat pump can provide free hot water. A device called a super heater transfers excess heat from the heat pump's compressor to the hot water tank. In the summer, hot water is provided free; in the winter, water heating costs are cut roughly in half.

While producing lower heating bills, geothermal heat pumps are quieter than conventional systems, and improve humidity control. These features help explain why customer surveys regularly show high levels of user satisfaction, usually well over 90 percent.

Geothermal heat pump systems allow for design flexibility, and can be installed in both new and retrofit situations. Because the hardware requires less space than that needed by conventional HVAC systems, the equipment rooms can be greatly scaled down in size, freeing space for productive use. Also, geothermal heat pump systems usually use the existing ductwork in the building and provide simultaneous heating and cooling without the need for a four-pipe system.

Architects and building owners like the design flexibility offered by GHP's. Historic buildings like the Oklahoma State Capital and some Williamsburg, Virginia, structures use GHPs because they are easy to use in retrofit situations and easy to conceal, as they don't require cooling towers.

GHP systems eliminate conventional rooftop equipment, allowing for more aesthetically pleasing architectural designs and roof lines. The lack of rooftop penetrations also means less potential for leaks and ongoing maintenance, and better roof warranties. In addition, the aboveground components of a GHP system are inside the building, sheltering the equipment both from weather-related damage and from potential vandalism.

Because a GHP system is so efficient, it uses a lot less energy to maintain comfortable indoor temperatures. This means that less energy is often created from burning fossil fuels than is needed to operate a GHP. According to the EPA, geothermal heat pumps can reduce energy consumption and corresponding emissions up to 44 percent compared to air-source heat pumps, and up to 72 percent compared to electric resistance heating with standard air conditioning equipment.

According to a study completed for the Geothermal Heat Pump Consortium (GHPC), buildings with GHP systems had average total maintenance costs ranging from 6 to 11 cents per square foot, or about one third that of conventional systems. Because the workhorse part of the system, the piping, is underground or underwater, there is little maintenance required. Occasional cleaning of the heat exchanger coils and regularly changing the air filters are about all the work necessary to keep the system in good running order.

These systems provide excellent zone space conditioning - different areas of the building heated or cooled to different temperatures simultaneously. For example, GHP systems can easily move heat from computer rooms (which need constant cooling) to the perimeter walls for winter heating in commercial buildings. School officials like the flexibility of heating or cooling just auditoriums or gymnasiums for special events rather than the entire school.

Because GHP systems have relatively few moving parts, and because those parts are sheltered inside a building, they are durable and highly reliable. The underground piping often carries warranties of 25 to 50 years, and the GHP's often last 20 years or more.

GHPs usually have no outdoor compressors or cooling towers, so the potential for vandalism is eliminated.