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 to heat or cool a home, while ground-source heat pumps - also known as geothermal - exchange heat with the ground, says Nick Vakay, service manager for highly rated Sila Heating & Air in Stoneham, Ma. "They're both more efficient than furnaces that use fossil fuels," he says. "But geothermal systems are the most efficient."

Bill Souza, president of highly rated Excel Energy Solutions in Somerville, Ma., says air-source heat pumps aren't common in Boston because Massachusetts' cold winters make them impractical. "They're less of an investment than a geothermal system," Souza says. "But we don't recommend them."

Depending on a home's existing system, Vakay says the savings a geothermal system offers can be impressive. "If you go from forced-air to geothermal, the payback can be less than five years," Vakay says, adding geothermal systems don't require much maintenance other than filter changes.

However, Souza warns that geothermal systems may not be viable for everyone. "A lot of homes in New England are built on the sides of mountains or on the water's edge," he says. "If we can't drill a hole in the ground, we can't put a geothermal system in." Souza estimates a geothermal system for a 2,000 square-foot-home will cost between $26,000 and $35,000, which can be offset by a 30-percent federal tax credit that's available until 2016.