Air-source heat pumps extract heat from outside air that is then used for heating indoor spaces during the colder months. They can also extract heat from indoors and expel it outside to cool indoor spaces during the warmer months. Air-source heat pumps, like a ductless mini-split, can be used to heat or cool single rooms (partial load) and whole homes (full load).

A geothermal heat pump functions like a conventional heat pump, by using high-pressure refrigerant to capture and move heat between indoors and out. The difference is that conventional systems gather their heat—and get rid of it—through the outside air. Geothermal systems, in contrast, transfer heat through long loops of liquid-filled pipe buried in the ground. Since the underground temperatures stay at approximately 50 degrees, it doesn't take as much effort for the system to heat the air to a comfortable temperature, making it the most efficient type of heat pump. In the summer, the system works in reverse to cool the air. 

Heat pump water heaters extract heat from the air surrounding the unit to heat water. They can replace electric or fossil fuel-powered water heaters that require much more energy to run efficiently— leading to big savings.