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Ground-source heat pump
Ground-source heat pump
Instead of burning fuels pumped out of the ground, like oil and gas, geothermal heat pumps mine the relatively constant temperatures just below the earth's surface.

The pumps, also called ground-source heat pumps, use a network of tubes to circulate fluid underground to retrieve warmth in the winter and disperse heat in the summer.

A geothermal system costs between $5,000 and $10,000 to install, according to Jim Bose, executive director of the International Ground Source Heat Pump Association. That's substantially more than a conventional heating system.

While the upfront cost is significant, it can be recovered in energy savings after as little as five years, according to the Department of Energy. After that, the pumps can provide 25 years of heating and cooling service with relatively low maintenance costs.

Indeed, a geothermal system has the potential to reduce energy bills by as much as 35%, Bose said. And those savings are attracting the attention of many homeowners faced with the possibility of a 20% increase in heating bills this winter.

The federal government's $300 tax credit for qualified geothermal heat pumps expired last year. Lawmakers have yet to decide whether or not renew or expand the tax credit.

NEXT: Passive solar

Last updated August 22 2008: 11:56 AM ET
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