A heat pump works by moving heat from the outside air via a compressor, which circulates refrigerant that absorbs heat and releases heat while traveling between indoor and outdoor units. Peter von Rittinger developed and built the first heat pump between 1855 and 1857.
A heat pump system is usually made up of two parts: a unit in the home called an air handler and an outdoor unit similar to an air conditioner. A heat pump system uses electricity only, which helps with sustainability because it does not use fossil fuels.
An advantage of using a heat pump is that, since it moves the heat instead of having to generate the heat, it is a lot more efficient. When the air is cold, the heat pump takes heat from the air outside and transfers it inside the home. When it's hot outside, the heat pump transfers the heat from inside the house outside.
Heat pumps can work very well in moderate climates, with no need for a supplemental fuel source, though a supplemental heating source may be necessary in colder climates. Geothermal heat pumps use pipes and water, which are buried underground, where the temperature stays relatively constant, to transfer heat via the water.