Heat pumps use electricity to draw heat from the air or ground outdoors and transfer it inside. As a result, heat pumps are more efficient in temperate regions than in cooler regions.
Pressure causes temperatures to rise. When air or a refrigerant is compressed, it warms up. Heat pumps use this law of physics to generate heat, which can then be vented throughout a home. This operation is similar to air conditioners, which instead use compression to send heat out of the home. Most heat pumps can also be reversed to function like air conditioners.
Heat pumps are better able to generate heat if the air outside is warmer, so they are more popular in regions where temperatures rarely drop below freezing. However, even if they cost a bit more to run in the coldest months, the efficiency provided by heat pumps in warmer months may make them a wise investment.
Because they may not be able to keep up if the temperature drops too much, heat pumps have an emergency heating mode. In addition to drawing heat from outside, heat pumps can use electrical resistance to generate extra heat, much like many central air-conditioning units. However, this operating mode is inefficient, so it is important to ensure that thermostats are not sending heat pumps into emergency mode unless it is necessary.