A heat pump may be the best way to heat a home for people living in climates where temperatures seldom drop below freezing as they are energy-efficient and produce a mild, even heat. Heat pumps are not as efficient in colder climates.
Most heat pumps work by transferring heat between indoor air and outdoor air. This allows them to cool indoor air in summer by transferring heat from the inside to the outside. The process is reversed in winter. Transferring heat is much more energy-efficient than generating it, but when outdoor air is cold, a heat pump cannot extract much heat from it to transfer indoors. Most heat pumps solve this problem by using electric resistance coils to generate extra heat as needed to make indoor air comfortable, but these coils are not as efficient as a gas furnace or oil burner.