Our quest to find alternative sources of energy is leading us to new frontiers.Ground-source heat pumps (GSHPs), often called “geothermal heat pumps,” are devices to exploit the relatively stable temperatures found just 5 feet (1.5 m) or more below the surface, either depositing or extracting low-intensity heat. Heat pump are basically air conditioners that can be run in reverse to provide heating as well as cooling.

GSHPs should not be confused with geothermal heat, which lurks roughly six miles below the surface, where the earth’s crust gives way to a layer of molten rock. This geothermal energy occasionally explodes to the surface as a volcano, creates natural geysers and hot springs, and, in places like Iceland, it is tapped to produce electricity.

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