A heat pump is a heating and cooling system that transfers thermal energy from one location to another instead of creating heat directly through combustion. Depending on its design and operating mode, a heat pump can move heat from outdoor air, the ground, or water into a building for heating. The same basic principle can also be reversed to remove heat from an indoor space.
Context
The technology developed from refrigeration and air-conditioning systems, which also use a refrigeration cycle to move heat. Modern heat pumps apply similar principles to residential buildings, commercial facilities, water heating, and some industrial processes.
A typical heat pump contains a closed circuit through which a refrigerant circulates. The refrigerant changes pressure and temperature as it moves through different components, allowing heat to be absorbed at one point and released at another.
How a heat pump works
The basic heat pump cycle involves four major stages: evaporation, compression, condensation, and expansion. During evaporation, the refrigerant absorbs heat and changes from a liquid into a vapor. The compressor then raises the vapor's pressure and temperature.
The hot, high-pressure refrigerant travels to a condenser, where it releases heat into the area being heated. It then passes through an expansion device, where its pressure drops before the refrigerant returns to the evaporator and repeats the cycle.
In heating mode, this process transfers available heat toward the building. In cooling mode, a reversing valve can change the direction of refrigerant flow so that heat is removed from the indoor space.
Main heat pump components
The main components work together as a continuous thermal transfer system:
Evaporator: Absorbs heat from the surrounding air, ground, or water.
Compressor: Raises the refrigerant pressure and temperature.
Condenser: Releases heat into the building or another heat-transfer medium.
Expansion valve: Reduces refrigerant pressure before the evaporation stage.
Reversing valve: Changes refrigerant direction in systems capable of both heating and cooling.
Fans or pumps: Move air or water through the heat-transfer system.
Controls and sensors: Monitor temperatures, pressures, operating conditions, and system demand.
The exact arrangement depends on the type of heat pump and whether it distributes heat through air, water, or another medium.
Importance
Heat pumps matter because buildings require substantial amounts of heating and cooling energy, while the way heat is produced affects overall energy use. A heat pump moves existing thermal energy rather than generating all of the delivered heat through combustion or resistance heating.
Energy efficiency is often described using measures such as coefficient of performance, or COP. A COP compares useful heating or cooling output with the electrical energy consumed under particular operating conditions. It is not a fixed number because performance changes with outdoor temperature, indoor temperature, system design, and operating conditions.
The International Energy Agency's recent analysis continues to identify heat pumps as an important electrification technology. Its 2026 analysis also notes continued deployment across buildings and growing use of industrial heat pumps at moderate temperature ranges.
Factors that influence efficiency
Heat pump efficiency depends on the temperature difference the system must overcome. When the heat source and required delivery temperature are relatively close, the system can generally transfer heat with less compression work than when the temperature difference is large.
Other factors include:
Outdoor or source temperature
Indoor temperature requirements
Building insulation and air leakage
Heat distribution method
Compressor design
Refrigerant characteristics
Defrost operation in cold conditions
Equipment sizing
Control settings
Maintenance and airflow
A heat pump installed in a poorly insulated building may therefore have different real-world energy performance from an otherwise similar system operating in a well-insulated building.
Heat pump types
Heat pumps are commonly classified according to their heat source and the way heat is distributed.
| Heat pump type | Heat source | Typical heat distribution |
|---|---|---|
| Air-source | Outdoor air | Air or water |
| Ground-source | Ground or buried heat exchanger | Water-based or air systems |
| Water-source | Groundwater, surface water, or another water source | Water or air |
| Air-to-water | Outdoor air | Heated water |
| Air-to-air | Outdoor air | Conditioned air |
| High-temperature | Air, water, ground, or recovered heat | Industrial or process heat |
Air-source heat pumps are widely used because they can exchange heat directly with outdoor air. Ground-source systems use buried heat exchangers, while water-source systems obtain thermal energy from an appropriate water source.
Recent Updates
Heat pump technology has continued to develop through improvements in compressors, controls, heat exchangers, refrigerants, and system integration. The broader market has not followed a uniform pattern, however, with adoption varying by region, building type, energy prices, climate, and policy conditions.
The IEA's 2026 Global Energy Review reports that worldwide heat pump sales declined slightly in 2025, while Europe experienced renewed growth. It also reports continued development of air-to-water, water-heating, and industrial heat pump applications.
Refrigerant changes
Refrigerants have received increasing attention because some substances used in cooling and heating equipment have high global warming potential. Regulatory changes in several markets are encouraging or requiring a transition toward refrigerants with lower climate impact.
Current alternatives include substances such as propane, carbon dioxide, ammonia, and selected lower-GWP fluorinated refrigerants. Their suitability depends on system design, operating temperature, safety classification, application, and applicable regulations.
The European Union's updated F-gas framework, for example, entered into application in 2024 and establishes a broader phase-down of hydrofluorocarbons while placing restrictions on certain equipment using fluorinated greenhouse gases. Such rules illustrate the wider movement toward lower-GWP refrigerants, although requirements differ between jurisdictions.
Smarter controls and system integration
Modern heat pumps increasingly use variable-speed compressors, electronic expansion valves, temperature sensors, and digital control systems. These technologies can adjust system operation according to changing heating or cooling demand.
Heat pumps are also being integrated with thermal storage, solar electricity, building-management systems, and other energy technologies. These developments are intended to coordinate heating and cooling demand with changing building conditions and electricity availability.
Laws or Policies
Heat pumps are affected by several categories of rules, including energy-efficiency requirements, equipment safety standards, refrigerant regulations, electrical requirements, building codes, and product labeling rules.
The exact requirements depend on the jurisdiction and application. Residential equipment, commercial systems, and industrial heat pumps may be subject to different technical requirements because their capacities, operating temperatures, refrigerant quantities, and installation conditions can differ substantially.
Refrigerant rules are an increasingly important part of heat pump regulation. Authorities may establish limits on the use of particular refrigerants, requirements for leak prevention, labeling provisions, recovery procedures, or qualifications for people handling refrigerants.
Energy-efficiency regulations can also specify testing procedures and performance metrics. These measures are important because heat pump efficiency can vary significantly depending on the conditions under which performance is measured.
International technical standards are commonly used to establish consistent methods for testing equipment performance, safety, and other characteristics. However, compliance with a technical standard does not by itself determine whether a particular installation meets every local requirement.
Tools and Resources
Several resources can help readers understand heat pump operation, energy performance, and technical specifications.
Heat pump sizing tools
Heat-loss and heat-load calculations can estimate the heating or cooling capacity required for a building. These calculations consider factors such as building dimensions, insulation, outdoor conditions, windows, ventilation, and internal heat gains.
Energy performance calculators
Energy calculators can compare estimated electricity consumption under different operating conditions. Results depend on assumptions such as climate, operating hours, electricity use, equipment efficiency, and building characteristics.
Manufacturer technical documents
Technical documentation can provide information about heating and cooling capacity, operating temperature ranges, refrigerant type, electrical requirements, sound levels, and performance ratings. Such documents should be read together with applicable installation requirements.
Energy-efficiency databases
Government agencies, standards organizations, and independent testing programs in various regions maintain databases or product directories containing efficiency information. These resources can help readers understand how equipment is tested and how reported performance figures should be interpreted.
FAQs
How does a heat pump work?
A heat pump works by transferring thermal energy through a refrigeration cycle. The system absorbs heat from a source, raises the refrigerant pressure using a compressor, releases heat at another location, and then reduces refrigerant pressure before repeating the cycle.
What are the main types of heat pumps?
Common heat pump types include air-source, ground-source, water-source, air-to-air, and air-to-water systems. They differ mainly in where heat is collected and how it is distributed.
Are heat pumps energy efficient?
Heat pumps can transfer more thermal energy than the electrical energy directly consumed by the compressor and other components under suitable operating conditions. Actual efficiency depends on temperature conditions, equipment design, installation, controls, and building characteristics.
What components are used in a heat pump?
The principal components include an evaporator, compressor, condenser, expansion valve, controls, sensors, and, in reversible systems, a reversing valve. Fans, pumps, heat exchangers, and electrical components may also be included.
What refrigerants are used in heat pumps?
Heat pumps can use several refrigerant types, depending on the system and application. Examples include propane, carbon dioxide, ammonia, and various fluorinated refrigerants. Selection is influenced by operating requirements, safety considerations, equipment design, and applicable regulations.