An air-source heat pump is an energy-efficient heating and cooling unit for the home that performs best in areas with sub-freezing winter temperatures. The device works by transferring heat from the air rather than converting it from fuel.
Air-source heat pumps include two copper coils, one outside the home and another inside, as well as a compressor. When heating, a liquid refrigerant in the outdoor coil draws heat from the air, releasing it as a gas, while the indoor coil converts it into a liquid. A reversing valve may be used to change the direction of heat transfer for cooling the home. Some models may include all coils outside the home while heat is transferred through a series of ducts.
Most air-source heat pumps that are not designed for cold climates use electric resistance coils to heat the home when the outside temperature dips below 40 degrees Fahrenheit. This type of heating is not cost effective, but users may install a back-up gas furnace to solve this problem. When choosing a heat pump, shoppers should look for the Energy Star label, which indicates that the unit has a high seasonal energy efficiency ratio and heating season performance factor. Buyers should install the unit away from windows and neighboring buildings due to the compressor's noise level.