A heat pump combines cooling and heating capability in one unit. When cooling, the heat pumps operates like an air conditioner, removing the heat from indoors and transferring it outdoors. In the winter the heat pump takes heat from the outdoors and transfers it inside your home. Even at freezing temperatures, there is still heat in the outdoor air that can be used to warm a home by using a heat pump. To augment the heat pump on very cold days, electric resistance heaters are installed in the indoor section of the unit.