What are the differences between air-source heat pumps and ground-source heat pumps? - Angie's List member Mark Schinman

Air-source heat pumps use the difference between outside and indoor air temperatures to heat or cool a home, while ground-source heat pumps - also known as geothermal - heat and cool by exchanging heat with the ground, says Brad Wentz, president of highly rated Buckeye Heating & Cooling in Worthington, Ohio. "They both save energy [compared to conventional systems]," he says. "But geothermal systems are the most efficient."

Jeff Persons, owner of highly rated Geo Source One in Plain City, Ohio, says geothermal systems are more practical in colder climates like Ohio's. "If we had constant 50 to 60 degree weather all winter, there would be minimal difference between the air-source and ground-source efficiency," he says. "However, since the air temperature varies and the ground temperature remains steady, geothermal is the most efficient option."

Depending on a home's existing system, Persons says the potential savings a geothermal system offers can be impressive. "It can show a savings of as much as 70 to 80 percent versus a gas furnace," he says.

Both Wentz and Persons say investing in a geothermal system is more expensive than an air-source heat pump. Persons estimates an average air-source system for a 2,000-square-foot home can cost $6,000 to $8,000, while a geothermal system can cost $21,00 to $23,000. However, he says a 30 percent federal tax credit is available until 2016 for geothermal systems.