Heat pump
A heat pump moves heat from one place to another for heating, cooling, or water heating. Because it transfers heat instead of making heat by combustion or resistance alone, it can deliver more heat energy than the electricity it uses.
What a heat pump is
A heat pump is a machine that transfers heat rather than creating it only from fuel or electrical resistance. In winter it can move heat from outdoor air, the ground, or water into a building. In summer, many heat pumps reverse direction and move heat from indoors to outdoors, working like an air conditioner.
How the cycle works
Most building heat pumps use a vapor-compression refrigeration cycle. A refrigerant evaporates at low pressure to absorb heat, is compressed to a higher pressure and temperature, condenses to release heat, and then passes through an expansion device so the cycle can repeat. A reversing valve lets many systems switch between heating and cooling.
Air-source systems
Air-source heat pumps exchange heat with outdoor air. They are common because they are easier to install than ground-source systems and can serve ducted, ductless, or mixed indoor equipment. Cold-climate models use improved compressors, controls, refrigerants, and defrost strategies to keep working in lower outdoor temperatures.
Ground-source systems
Ground-source, or geothermal, heat pumps exchange heat with the ground or groundwater through buried loops or wells. Because ground temperatures are steadier than outdoor air, these systems can be very efficient. They usually cost more to install because of drilling, trenching, loop design, and site constraints.
Efficiency language
Heat-pump performance is often described with coefficient of performance, seasonal energy efficiency ratio, heating seasonal performance factor, or related ratings. A coefficient of performance above 1 means the system is delivering more heat than the electrical energy it consumes, because it is moving existing heat.
Sizing and buildings
A heat pump works best when it is matched to the building's heating and cooling loads. Insulation, air sealing, windows, duct quality, radiator size, indoor distribution, and climate all affect comfort and energy use. Oversized or undersized systems can cycle poorly, use backup heat too often, or leave rooms uncomfortable.
Refrigerants
The refrigerant is central to the heat pump cycle. It must evaporate and condense at useful temperatures, work safely within equipment pressures, and meet environmental rules. Refrigerant leakage, global warming potential, flammability, toxicity, and service practices are important parts of heat-pump design and policy.
Grid and climate context
Heat pumps can reduce building emissions when they replace fossil-fuel heating and run on cleaner electricity. Their grid impact depends on weather, building efficiency, controls, peak demand, and local power generation. Smart controls, thermal storage, and weatherization can make electrified heating easier to integrate.
Why it matters
Heating and cooling are major energy uses in buildings. Heat pumps matter because they combine familiar refrigeration physics with electrification, letting one device provide efficient heating and cooling while supporting cleaner power systems and more flexible building design.