What is a heat pump? Types, efficiency, install for UK homes

A heat pump is a heating system that transfers heat from an external source — typically the outside air or the ground — into your home, rather than generating heat by burning fuel. It works using the same refrigerant cycle as a fridge or air conditioning unit, compressing and expanding refrigerant gas to extract thermal energy from even cold outdoor air and move it indoors. For every unit of electricity the system consumes, a well-designed heat pump typically delivers three to four units of heat in return, making it significantly more efficient than a conventional boiler. Air source heat pumps are the most widely installed type in the UK and sit outside the property as a compact fan unit. Ground source heat pumps draw heat from pipes buried in the ground and offer higher efficiency but require more space and a larger upfront investment. Both types can provide space heating and domestic hot water for most UK homes.

Air source heat pumps extract thermal energy from outdoor air and are by far the most commonly installed type in the UK, accounting for around 99% of retrofit installations. They require only a small external unit and are straightforward to install on most properties. Ground source heat pumps use a network of pipes buried in the garden or drilled vertically into the ground to extract heat from the earth, which maintains a more stable temperature year-round than the air. This makes ground source systems slightly more efficient, but they cost significantly more to install — typically £28,000 to £34,000 compared to £10,000 to £15,000 for an air source unit — and require sufficient outdoor land area. For most urban and suburban UK homes, an air source heat pump is the practical and cost-effective choice. Ground source systems are better suited to rural properties with large gardens or land.

Air source heat pump installations in the UK typically cost between £10,000 and £15,000, including the unit, labour, and associated plumbing work such as a new hot water cylinder. Ground source heat pumps are considerably more expensive, generally ranging from £28,000 to £34,000 depending on whether a horizontal ground array or vertical borehole is required. These figures can be reduced significantly through the Boiler Upgrade Scheme (BUS), which offers a £7,500 grant towards eligible installations in England and Wales, and similar support is available in Scotland through the Home Energy Scotland scheme. Some mortgage providers also offer cashback of up to £2,000 for heat pump installations through approved schemes. The final cost will depend on property size, existing heating infrastructure, whether radiator upgrades are needed, and local installer rates. Always get at least three quotes from MCS-certified installers before committing.

Most UK homes are suitable for a heat pump, though the system performs best in well-insulated properties where heat loss through walls, windows, and the roof is minimised. Good insulation allows the heat pump to operate at lower flow temperatures, which is where it delivers the greatest efficiency. Homes with cavity wall insulation, loft insulation, and double glazing are well placed for a straightforward installation. Older or solid-wall properties may benefit from insulation improvements before installation to get the most from the system. You will also need a small amount of outdoor space for an air source unit — typically a flat, firm surface with good airflow around it — and a hot water cylinder if your existing setup is a combi boiler. A qualified MCS-certified installer will carry out a heat loss survey before specifying the right system for your home.

Yes, a correctly sized heat pump can replace a gas boiler entirely, providing both space heating and domestic hot water for the whole property. Unlike a combi boiler, a heat pump requires a hot water cylinder to store heated water, so this will need to be factored into the installation if your current system is combi-based. Some homeowners opt for a hybrid heating system during the transition, which combines a heat pump with the existing boiler — the boiler provides backup on extremely cold days or when peak demand is high, while the heat pump handles the majority of the heating load. A full replacement with a heat pump is the more carbon-efficient long-term solution, particularly as the electricity grid continues to decarbonise. For properties on mains gas, the running costs of a heat pump are broadly comparable to a gas boiler at current energy prices, and the gap is expected to close as government policy shifts in favour of electrified heating.

Heat pumps are compatible with radiators, but they operate at lower flow temperatures — typically 35 to 55°C — compared to the 60 to 75°C delivered by a conventional gas boiler. This means existing radiators need to be large enough to emit sufficient heat at those lower temperatures. In many properties, particularly those built in the last 20 years where radiators tend to be oversized relative to the boiler output, the existing radiators will work without replacement. Older properties with smaller single-panel radiators may require some or all of them to be upgraded to larger double-panel or low-temperature models to maintain comfort levels. Underfloor heating is an ideal distribution system for heat pumps due to its large surface area and low flow temperature requirements. A heat loss survey carried out by a qualified installer will identify whether radiator upgrades are needed before the heat pump is specified.

Heat pump efficiency is measured by the Coefficient of Performance (COP), which expresses how many units of heat are produced for each unit of electricity consumed. A well-designed and properly installed system typically achieves a COP of 3 to 4, meaning it delivers three to four times more energy as heat than it uses in electricity. The Seasonal Coefficient of Performance (SCOP) measures average efficiency across the whole heating season and is a more useful real-world figure. Best-practice installations with correctly sized radiators and good insulation can achieve SCOP values of 4.5 or higher, while the UK average is closer to 3.0 due to variation in installation quality. Heat pump efficiency drops slightly as outdoor temperatures fall, but modern units continue to operate effectively well below 0°C, which is rarely a problem in UK conditions. Properly sizing the system and keeping flow temperatures as low as possible are the two most important factors in achieving peak efficiency.

At current UK energy prices, running costs for a heat pump are broadly comparable to a gas boiler for an average home, with government modelling suggesting a saving of around £100 per year for a typical property switching from gas. The comparison depends heavily on your electricity and gas tariff, the efficiency of your installation, and the insulation level of your home. For properties currently heated by oil or LPG, the savings are more significant, as heat pumps are typically far cheaper to run than either fuel type. Smart electricity tariffs, which offer cheaper overnight rates, can improve heat pump running costs further, particularly if you can pre-heat your home or hot water cylinder during off-peak hours. As the electricity grid decarbonises and policy moves to rebalance the electricity-to-gas price ratio, heat pumps are expected to become increasingly cost-competitive with gas. Over the full lifecycle — typically 15 to 20 years — heat pumps represent strong value against fossil fuel alternatives.

Yes, modern heat pumps work effectively in cold weather and are designed to operate in outdoor temperatures well below 0°C. Most units continue to deliver reliable heating down to around -15°C to -20°C, which is far below anything typically experienced in the UK. Efficiency does reduce slightly as temperatures fall — the greater the difference between the outdoor temperature and the target indoor temperature, the more electricity the system uses — but this rarely causes comfort issues in UK conditions. In very cold spells, some systems include a backup immersion heater or supplementary electric element to maintain performance. Given that the UK climate rarely drops below -5°C even in winter, cold weather performance is not a significant practical concern for most UK homeowners. Correct sizing by the installer ensures the system is specified to handle the full range of temperatures your property will encounter.

The main government grant available in England and Wales is the Boiler Upgrade Scheme (BUS), which provides £7,500 towards the installation of an eligible heat pump in homes and small businesses. The installation must be carried out by an MCS-certified installer, who will apply for the voucher on your behalf. In Scotland, the Home Energy Scotland Grant and Loan scheme offers grants of up to £7,500, rising to £9,000 for qualifying rural households. Applications under the BUS have grown significantly since the grant was increased in 2023, and the scheme is currently funded through to 2028 with over-allocation authorised to meet rising demand. Some banks and mortgage providers also offer cashback of up to £2,000 for heat pump installations made through approved schemes. To check current eligibility and apply, the installation must be on a property with a valid EPC that does not recommend loft or cavity wall insulation as a priority improvement.

In most cases, air source heat pumps can be installed under permitted development rights without requiring a full planning application, provided the installation meets certain conditions. The unit must comply with the relevant MCS Planning Standards, and the installation must be the first heat pump fitted at the property. Recent changes to permitted development rules have removed the previous requirement for the unit to be sited at least one metre from the property boundary, and the permitted size limit has been increased. Installations on listed buildings, in conservation areas, or within certain designated landscapes may still require planning consent, so it is worth checking with your local planning authority if your property falls into any of these categories. Ground source heat pumps generally do not require planning permission for the pipe installation itself. Your MCS-certified installer will be familiar with the relevant requirements and can advise on your specific property before work begins.

A well-maintained heat pump typically lasts between 15 and 20 years, with some systems operating reliably for 25 years or more depending on the brand, installation quality, and how the system is used. Most manufacturers require an annual service to maintain the warranty, and this yearly check is important for keeping the system running at peak efficiency and catching any minor issues before they develop. Ground source heat pumps tend to have a longer lifespan than air source units, partly because the buried pipework has no moving parts and can last 50 years or more. The compressor is the component most likely to require attention over the system's life, and replacement compressors are available for most major brands. Compared to a gas boiler, which typically needs replacing after 10 to 15 years, a heat pump's longer lifespan contributes to a lower total cost of ownership over time. Keeping filters clean and ensuring the outdoor unit has good airflow will help extend service life.

Modern air source heat pumps are significantly quieter than older models and comparable to the noise level of a standard air conditioning unit. The outdoor fan unit typically produces around 40 to 60 decibels at one metre distance — broadly equivalent to moderate rainfall or a quiet conversation. At typical garden distances, this is unlikely to cause any disturbance. The internal components of the system operate at around 18 to 30 decibels, which is barely audible. Siting the unit thoughtfully — away from bedroom windows and not directly against a boundary wall — is good practice and will minimise any potential nuisance to neighbours. The MCS Planning Standards specify noise limits that all certified installations must meet, and your installer will confirm compliance as part of the design process. Hybrid systems that retain a gas boiler for supplementary use may also reduce the hours the heat pump fan runs, which can help in noise-sensitive locations.

Many heat pumps are reversible and can provide active cooling in summer by reversing the refrigerant cycle to extract heat from inside the home and transfer it outdoors — operating on the same principle as an air conditioning unit. Air-to-air heat pumps deliver cooling directly into the room and are particularly effective for this purpose. Air-to-water heat pumps, which connect to a wet central heating system, can also provide passive cooling by circulating cooled water through underfloor heating circuits or fan coil units, though this is less common in standard UK residential installations. The UK government's Warm Homes Plan has moved to support the rollout of air-to-air heat pumps that provide a combined heating and cooling function, recognising their value as summer temperatures in the UK continue to rise. If summer cooling is a priority, discuss this requirement with your installer at the design stage so the correct system type is selected.

Heat pumps require less maintenance than a gas boiler but do need an annual service to keep them running efficiently and to maintain the manufacturer warranty. The yearly service typically covers checking refrigerant levels, inspecting electrical connections, testing controls and sensors, cleaning filters, and verifying that the system is operating within designed parameters. Between services, the main homeowner tasks are keeping the outdoor unit clear of debris, leaves, and snow, and ensuring adequate airflow around the fan. The indoor hot water cylinder and associated controls should also be checked periodically. If you are receiving support through the Boiler Upgrade Scheme, keeping your heat pump in good working order and serviced in line with manufacturer requirements is a condition of the grant. Most heat pump manufacturers and installers offer annual service plans, which provide peace of mind and protect your investment over the full life of the system.