Geothermal Heating

Geothermal heating is the direct use of the heat stored inside the Earth for heating applications, without first converting that heat into electricity, a practice people have relied on since the Paleolithic era in the simple form of bathing in hot springs. In volcanically active regions, naturally hot groundwater can be piped straight into heating systems, while in cooler regions a ground source heat pump circulates fluid through underground loops to draw out and concentrate the ground heat instead. As of 2007 the world operated roughly 28 gigawatts of geothermal heating capacity, with about 70 countries using some 270 petajoules of it in 2004, led by China, and it supplies district heating networks in cities such as Reykjavik, Boise and Klamath Falls along with greenhouses, spas, industrial processes and road snow melting.