Heat pumps are another heat source for forced air heating systems. Electric heat pumps are more energy efficient than other electrical heating systems because they use electricity to move heat, instead of producing heat. The most common heat pumps are air-to-air systems. They extract heat from the outside air and transfer it to the inside air. Other systems include solar-assisted, water-source and ground-source heat pumps. The principles for air-to-air systems discussed below also apply to other types of heat pumps. It may seem hard to believe that heat from outside air can heat your home during freezing weather. As long as the air temperature is greater than absolute zero, -460 degrees F., there is some heat in the air. At 32 degrees F., air possesses 88% of the heat that it has at 100 degrees F.
