How it works
Essentially, geothermal energy is heat (thermal) derived from the earth (geo). Heat pumps dug deeply into the ground allow the warmer surrounding earth to heat a cold building in winter (and the reverse in summer). Very near geothermal resources, hot groundwater can be piped in directly to heat buildings, pools, and greenhouses, and even melt snow on sidewalks and roads. Four western states—California, Hawaii, Nevada, and Utah—use geothermal resources to produce electricity for community grids.

Pros

  • Geothermal plants don’t burn fossil fuels to generate electricity. An EPA report has suggested that geothermal heat pumps are the most energy-efficient, environmentally friendly, and cost-effective systems available for heating and cooling interior spaces.

Cons

  • Geothermal resources—underground steam, vents, geysers—exist in 16 (mostly Western) states. But only a few plants currently tap this energy.
  • If you live where there are no geological caches of geothermal energy, you’re limited to using a household geothermal heat pump.

Ecobonus
U.S. greenhouse gas emissions are reduced by more than 1 million metric tons of carbon dioxide each year by the current use of geothermal heat systems.

Best choice for …
people interested in heating and cooling their homes affordably, efficiently, and with the environment in mind—no matter where they live. Those living in Northern and Western states can take advantage of electricity generation options, as well.

Approximate cost
To install a geothermal heat pump for the average home, which uses a 3-ton-unit heating system, you’d spend about $7,500. (A more traditional pump system with air conditioning costs about $4,000.) Maintenance costs for geothermal heat pumps tend to be lower thereafter because the pumps have very few breakable parts.

Resource
DOE Geothermal Technologies Program
www.eere.energy.gov/geothermal/
Outlines geothermal energy basics.