In the past, nearly all commercial geothermal exploration efforts in the U.S. have been directed at finding high-temperature hydrothermal systems over 200°C (392°F) for the commercial generation of electricity.

Current U.S. geothermal electric power generation totals approximately 6.94 x 10¹⁶ J/yr (2,200 MW), or about the same as four large coal-fired or nuclear power plants. U.S. geothermal power units are located in California, Nevada, Utah, and Hawaii.

In recent years, more low- and moderate-temperature systems have been explored for space heating applications in buildings and greenhouses, and for electricity generation using modular, binary power plants. Uses for low- and moderate-temperature resources can be divided mainly into two categories: direct use and ground-source heat pumps. Moderate-temperature resources, under favorable circumstances, can be used to generate electricity using binary technology.

Direct Use
Direct use, as the name implies, involves using the heat in the water directly (without a heat pump or power plant) for such things as heating of buildings, industrial processes, greenhouses, aquaculture (growing of fish) and resorts.

Direct-use projects generally use resource temperatures between 40°C to 150°C (104°F to 302°F). Current U.S. installed capacity of direct-use systems totals 1.48 x 10¹⁶ J/yr (470 MW) or enough to heat 40,000 average-sized houses.

Ground-source heat pumps
Ground-source heat pumps use the earth or groundwater as a heat source in winter and a heat sink in summer. Using resource temperatures of 4°C (40°F) to 38°C (100°F), the heat pump, a device which moves heat from one place to another, transfers heat from the soil to the house in winter and from the house to the soil in summer. Accurate data is not available on the current number of these systems; however, the rate of installation is thought to be between 10,000 and 40,000 per year.