An AC unit works on the principle that when a material goes through a phase change, it can absorb heat from its surroundings. Thus, when the freon circulating through the air conditioning unit hits the evaporator coil, it vaporizes and absorbs heat from the air in your home. Your AC fan then pushes this air down your ducts to cool your house. Typically, you have evaporator coils on the inside of your house and condenser coils on the outside, but if you flip the function of the coils, you can use the same unit to both heat and cool your home. In some climates, this means that you can use one machine to both heat and cool your home.
What Is a Heat Pump?
An air conditioner will have dedicated coils, so the function of evaporator and condenser coils cannot be switched. Thus, you can only use the machine to cool your home. A heat pump will have a switch that allows the coils inside your house to work as condenser coils to expel heat into your home and the coils outside your home to be used as evaporator coils to absorb heat from the outside air. Even when the air outside of your home feels unbearably cold, there is often enough heat in the air for AC coils to be able to absorb enough heat to warm up your home.
What Temperature Is Best for Heat Pumps?
Even though a good heat pump can extract heat from the air outside your home even if the temperatures hover around freezing, a heat pump will be most effective at moderate temperatures.
The Efficiency of a Heat Pump?
Because a furnace burns a fuel to heat your home, it will never be more than 100% efficient. On the other hand, a heat pump only has to move heat from one location to another. This is a much easier process, which means that a heat pump can be as much as 250% efficient.
In that a heat pump should be much more efficient than a furnace, and in that you only have to buy one piece of equipment to both heat and cool your home, a heat pump can help you save money as compared to buying a furnace. On the other hand, if you live in an area that will have several days during the winter with sub-zero temperatures, then your heat pump will not be as efficient as it should be. Thus, heat pumps are a good choice for homes in moderate climates.