A heat pump is similar to an air conditioner in that it relies on heat transference to condition the air. During warmer temperatures a heat pump works just like an air conditioner by absorbing hot interior air and transferring it outside. During colder temperatures, the heat pump absorbs heat from outside air and transfers it inside. While heat pumps are typically more energy efficient than most electrical resistance heaters, their efficiency is compromised by decreases in average outside temperatures. Thus, while heat pumps are considered energy efficient options for heating and cooling in southern states, they are not commonly used in northern states.