Heat pumps are not effective in all climates. When temperatures are low for an extended period, the continual operation becomes more expensive and does not provide sufficient heat. Other disadvantages include installation costs, and the fact that the air from the unit is often not as warm as that from other heat sources.
Heat pumps work by moving heat from a cold area to a warmer one. When the temperature differential is small, they are very efficient, and provide more heat energy than a resistance furnace with a similar amount of power. However, as the difference between indoor and outdoor temperatures grows larger, heat pumps take more energy to move the heat. Most units overcome this problem using a backup source of heat, such as a gas or resistance furnace. This heat source also operates when the heat pump is in the defrost cycle.
Additionally, the air exiting the air ducts from a heat pump is not as warm as the air from a traditional furnace. Some owners report the air from the ducts is cold. The problem sometimes requires redirecting vents to blow away from room occupants.
Installing a heat pump is sometimes more expensive than installing a traditional furnace. While the owner eventually recovers the money in utility savings, the initial cost keeps some consumers from installing the systems.