What is a heat pump and how does it work?

A heat pump is an electrically powered system that moves heat from one place to another. For home heating, it can collect energy from outdoor air, the ground or water and raise it to a temperature that warms rooms or stored hot water.

It does not need outdoor air to feel warm to a person. There can still be usable energy in cold air, although equipment performance changes with the operating conditions. A suitable system must be designed for the building and relevant winter conditions. Reviewed 29 October 2026.

How does a heat pump work?

A conventional heat pump uses a refrigerant circuit. The refrigerant absorbs heat at the source, a compressor raises its pressure and temperature, and a heat exchanger transfers useful heat to the destination. An expansion process prepares the refrigerant to collect more heat and repeat the cycle.

Electricity runs the compressor and other components. Because the system moves heat as well as using electrical energy, it can deliver more heat than the electricity it consumes. That does not create energy from nothing: the additional heat has come from the source.

Stage	What happens	What it means for the homeowner
Collect	Heat is absorbed from air, ground or water	Source conditions affect performance
Compress	Electricity drives a compressor	Electrical consumption forms part of the running cost
Deliver	Heat transfers to the heating system or indoor air	Emitters and water temperatures matter
Repeat	Refrigerant returns to collect more heat	Controls match operation to demand

The Energy Saving Trust heat-pump guide explains the main technologies. The cycle is the starting point; the full installed design determines the household experience.

The main types

Type	Heat source	How heat commonly reaches the home
Air-to-water	Outdoor air	Water-filled radiators, underfloor heating and domestic hot-water storage
Air-to-air	Outdoor air	Indoor fan units or designed air distribution; hot water is usually separate
Ground source	Buried collector or another designed ground connection	Usually a compatible water-based heating system
Water source	A suitable water resource	A system designed around its source, permissions and building

“Air source” can include both air-to-water and air-to-air. Check which is meant when comparing quotations. A price for heating one room with an indoor fan unit is not equivalent to supplying every room and domestic hot water.

Read our dedicated air-source buying guide, air-to-air guide and ground-source guide.

COP, SCOP and real-world efficiency

COP is heat output divided by electrical input under stated conditions. A COP of 3 means three units of heat for each unit of electricity within that measurement boundary. It is not a fixed property that remains unchanged all year.

SCOP is a standardised seasonal product metric. Measured seasonal performance describes an installed system over a period, with particular heat and electrical inputs included. The boundaries need checking before comparing figures.

For example, ignoring a backup heater or circulation pump can make one result appear better than a complete-system measurement. A favourable laboratory COP should not be used as a guaranteed annual bill calculation. OpenEnergyMonitor explains the measurement principles.

Illustrative image; equipment, layout and requirements are specific to the proposed installation.

Does a heat pump work in winter?

Appropriately selected systems can work in cold weather. Ask what output the proposed equipment supplies at your local design outdoor temperature and the heating-water temperature required by the emitters.

The statement that a unit can operate at a low temperature does not establish that it meets your house's heat requirement at that temperature. The building's heat loss, equipment output and any backup provision need to be considered together.

Air-source equipment can frost and periodically defrost. Follow the manufacturer's explanation of normal operation; persistent ice or failure to restore heating needs investigation rather than being treated as normal indefinitely.

Will it work with radiators?

Potentially. Existing emitters must deliver each room's required heat at the proposed flow, return and room temperatures. Some can stay; selected rooms may need changes. Underfloor heating is one possible arrangement, not a universal requirement.

Ask for a room-by-room heat-loss calculation and emitter schedule. The heat-loss toolkit explains why those assessments belong together.

Hot-water supply needs its own planning. A conversion from a combi boiler commonly introduces storage, but the exact configuration depends on the system. Ask how the proposed arrangement covers consecutive showers, baths and recovery.

What does it cost to install and run?

Installation depends on the complete work: equipment, hot-water provision, emitter and pipework changes, electrical work, outdoor preparation, commissioning and making good. Funding depends on the property, technology and UK nation.

Running costs depend on useful heat demand, achieved seasonal efficiency and actual electricity prices. More efficient energy use does not automatically mean cheaper energy where fuels have different prices.

For an original illustration, 12,000kWh of useful heat at seasonal efficiency 3 requires 4,000kWh of electricity. At an assumed 25p/kWh, that costs £1,000 in heating energy, excluding other household electricity, charges and maintenance. It is not a typical-house promise.

Use our installation-cost guide and running-cost calculator to compare your own inputs.

What should you check before buying?

Ask for a complete design covering rooms, hot water, equipment positions and controls. Resolve the relevant planning, ownership and electrical questions. Compare surveyed quotations with the same work included and obtain the service and fault-support arrangements in writing.

The system should meet agreed comfort requirements, rather than requiring you to accept cold rooms because the technology is different. Make the design assumptions and route for reviewing poor performance part of the purchase discussion.

Heat pump FAQs

Is a heat pump an electric heater?

It uses electricity, but moves environmental heat rather than relying entirely on direct electrical resistance. Ordinary electric heaters and heat pumps therefore have different consumption for the same useful heat under appropriate conditions.

Can it cool the house too?

Some systems can, but the complete installation must support it. Many air-to-air systems provide cooling; a radiator-based arrangement should not be assumed suitable without specific design and condensation control.

Are old homes excluded?

No architectural age alone settles suitability. The building, emitters, equipment locations and practical work need assessment.

Do I have to keep it running all day?

The right schedule depends on the design, building, controls and tariff. Leaving a system available is different from forcing continuous heat production.

Is it guaranteed to save money?

No. Compare total costs using realistic demand, efficiency and prices, with a cautious case as well as an optimistic one.

Related guides for your next step

Our heat pump glossary explains COP, SCOP, SPF and the other terms used in quotations.

The same heat-moving principle also appears in laundry appliances; see our separate heat pump tumble dryer comparison for appliance buying advice.

Sources and method

This explanation uses the linked technical guidance. The energy example is our own calculation, not a measured installation. Images are illustrative rather than evidence of product testing.

Images are AI-generated editorial illustrations.