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As a second-generation heating and air-conditioning contractor, I've installed hundreds of conventional hvac systems. But I also like to experiment, so when I first heard about geothermal, or ground-source, heat pumps back in 1979, I decided to try the technology out. Those early geothermal systems I installed are still working, providing low-cost heating and cooling. I now specialize in the technology, and with support from local electric utilities, I install over 120 systems a year — two or three a week. Ground-source heat pumps work on the same principle as a refrigerator or air conditioner: They concentrate and move heat rather than creating it. But unlike the air-source heat pumps commonly used in the South for heating and cooling, groundsource heat