In the simplest use of ground-source heating and cooling, a tube runs from the outside air, under the ground, and into a house's ventilation system. More complicated but more effective systems use compressors and pumps, like in electric air conditioning systems, to maximize the heat transfer. A study by the Environmental Protection Agency found that they are as much as 72 percent more efficient than electric heating and air conditioning systems. About 150,000 ground-source heat pumps had been installed by 1992, with the number growing by about 30,000 each year. While this is significant, it is less than 1 percent of the heating and cooling market.
Heat pumps have higher up-front costs.
Finally, many heating and cooling installers are just not familiar with the technology. Ground-source heat pumps are catching on in some areas though. In rural areas without access to natural gas pipelines, homes must use propane or electricity for heating and cooling. Heat pumps are much less expensive to operate, and since buildings are widely spread out, installing underground loops is not a problem. Underground loops can be easily installed during construction of new buildings as well, resulting in savings for the life of the building.