illustration of how geothermal pump works
An electrically powered, geothermal heating and cooling system transfers heat between your house and the earth using fluid circulated through long loops of underground pipe.
How It Works

Given all the attention being paid to solar power these days, you might be surprised to learn that one of the most promising solutions to high energy costs isn't up in the sky but buried deep under your lawn. Superefficient geothermal heat pumps provide clean, quiet heating and cooling while cutting utility bills by up to 70 percent. "With this technology, everybody could be sitting on top of their lifetime energy supply," says TOH plumbing and heating expert Richard Trethewey.

In principle, a geothermal heat pump functions like a conventional heat pump, by using high-pressure refrigerant to capture and move heat between indoors and out. The difference is that conventional systems gather their heat—and get rid of it—through the outside air. Geothermal systems, in contrast, transfer heat through long loops of liquid-filled pipe buried in the ground.

As our cave-dwelling ancestors discovered long ago, if you go far enough underground, the earth's temperature stays at a constant 50 degrees or so, no matter how hot or cold it gets outside. So while a conventional "air-source" heat pump struggles to scavenge heat from freezing winter air or to dump it into the summer swelter, its "ground-source" counterpart has the comparatively easy job of extracting and disbursing heat through the 50-degree liquid circulating in its ground loop. That's why it takes only one kilowatt-hour of electricity for a geothermal heat pump to produce nearly 12,000 Btu of cooling or heating. (To produce the same number of Btus, a standard heat pump on a 95-degree day consumes 2.2 kilowatt-hours.) Geothermal systems are twice as efficient as the top-rated air conditioners and almost 50 percent more efficient than the best gas furnaces, all year round.

Another advantage is that there's no need for a noisy outdoor fan to move air through the compressor coils. Geothermal units simply pump liquid, so they can be parked indoors, safe from the elements. Most come with 10-year warranties, but they can last much longer. In the 29 years since Jim Partin, one of the technology's earliest adopters, installed one in his Stillwater, Oklahoma, house, he's replaced only two contact switches.

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