Heat Pumps

Heat Pumps: The Full UK Guide

A heat pump is a machine that moves heat rather than making it. It takes low-grade warmth from the air outside, the ground beneath a garden or a body of water, and lifts it to a temperature that can heat a home and its hot water. Because it moves heat instead of burning fuel to create it, a heat pump typically delivers three to four units of heat for each unit of electricity needed to run it¹. That ratio is the single most important number in the whole subject: it is why a heat pump can heat a home using far less energy than any electric heater, and why its running costs depend so heavily on the price of electricity.

For a UK household, the practical picture is this. Heat pumps are technically suitable for most UK homes if installed appropriately². The government pays homeowners in England and Wales a £7,500 grant towards installing one through the Boiler Upgrade Scheme³. Installation costs run higher than a like-for-like boiler replacement, and the work needs a correctly sized system, adequate insulation and emitters, radiators or underfloor heating, that can deliver heat at lower temperatures than a gas boiler uses. This guide sets out all of it: how the technology works, the types sold in the UK, costs, grants, the planning and building rules, and where heat pumps genuinely fall short.

Heat pumps transfer existing warmth instead of generating it

The legal definition used across the UK's building regulations is precise about what a heat pump is: "a machine, device or installation that transfers heat from natural surroundings such as air, water or ground to buildings or industrial applications by reversing the natural flow of heat such that it flows from a lower to a higher temperature"⁷. That definition appears in the Building Regulations (Northern Ireland) 2012 and in the equivalent Welsh and EU-derived provisions, and every part of it matters to a householder.

Heat naturally flows from warm to cold. A heat pump reverses that flow. An air source heat pump, for example, moves heat from the air to a hot water supply⁸, taking warmth out of outside air that may feel cold to a person but still holds usable energy, and delivering it into water that circulates through radiators or underfloor pipes. Most heat pumps use an electrically driven compressor to do this⁹: the compressor squeezes a refrigerant, raising its temperature, and the heat is transferred into the home's heating water. The refrigerant then expands, cooling sharply, and the cycle begins again.

This is the same principle as a refrigerator, run in reverse. A fridge moves heat out of its cabinet and dumps it into the kitchen; a heat pump moves heat out of the garden or the street and dumps it into the home. The electricity the unit consumes is not turned into heat directly, as in an electric fan heater. It is spent driving the cycle, and for every unit spent, several units of heat are moved indoors.

One physical rule shapes everything else on this page: heat pumps operate more efficiently when the source temperature is higher and the sink temperature is lower⁹. In other words, a heat pump works best when the outside air or ground is relatively warm and the water it must deliver is relatively cool. That is why flow temperature, covered later in this guide, is the hinge on which both efficiency and running costs turn.

Matching air, ground and water source systems to your property

There are three types of domestic heat pump where permitted development rights apply: air source, ground source and water source¹⁰. All three do the same job by the same principle. What differs is where the heat comes from, and what that means for cost, space and the work involved.

Air source heat pumps absorb heat from the outside or surrounding air and transfer it into useable heat in the home for space or water heating, or both¹¹. They are the most common type in the UK because they are the cheapest and simplest to install: an outdoor unit, typically the size of a small suitcase, connected to the home's heating water. Within air source, the main split is between air-to-water systems, which transfer heat drawn from surrounding air to water in a wet central heating system¹², and air-to-air systems, which blow warmed or cooled air directly into rooms. Air-to-air systems are treated differently by some schemes: under ECO4, an air-to-air system is not considered a renewable system¹².

Ground source heat pumps transfer energy from the natural heat stored in the earth to heat the home and domestic hot water¹¹. Pipes are laid in trenches or drilled as boreholes, and because the ground stays at a steadier temperature than the air through the year, the heat source is more stable. The trade-off is cost and disruption: the ground array is the bulk of the work. A ground source heat pump may also be comprised of a shared ground loop, considered as a district heating variant measure type under ECO4¹², which allows homes, particularly in flats or dense terraces, to share one array.

Water source heat pumps draw heat from a river, lake, large pond or groundwater. They need access to a suitable body of water, which limits them to a small share of homes, but where the water source is available the temperature is stable and the system can be very efficient.

Fixed air source heat pumps can be reversed so that they draw heat from inside a building, providing cooling during the summer as well as indoor heating for colder periods of the year¹¹. That reversibility is a genuine difference from a boiler, which can only ever heat.

Each type has its own detailed page: air source heat pumps, ground source heat pumps, water source heat pumps, air-to-air heat pumps, air-to-water heat pumps, hybrid heat pumps and high-temperature heat pumps.

Three to four units of heat per unit of electricity used

The headline figure is consistent across independent and official guidance, with some variation in the exact ratio. Which? states that heat pumps typically deliver three to four units of heat for each unit of electricity needed to run them¹. The Development Bank of Wales says the same: for every unit of electricity they use, heat pumps typically produce three to four units of heat¹³. Northern Ireland's official consumer guidance says heat pumps can usually deliver three units of heat for every unit of electricity used, and that air source heat pumps typically produce three or more units of heat for every unit of electricity¹⁴.

The more conservative figure comes from Pendle Council's guidance, which states that an air source heat pump will supply 2 to 3 units of heat for one unit of electricity⁸. The difference between that and the three-to-four figures is not a disagreement about physics. It reflects real conditions: the ratio falls when the outside temperature drops, when the system has to deliver hotter water, or when an installation is poorly matched to the home.

What this ratio means for a household is simple. A gas boiler converts at most roughly one unit of heat from each unit of fuel it burns, since some heat always goes up the flue. A heat pump delivers several units of heat per unit of electricity. Whether that translates into lower bills depends on the relative price of electricity and gas, which is why the policy discussion, covered later, keeps returning to the price gap between the two.

The efficiency figure a buyer will actually see on paperwork is a seasonal one, usually a SCOP, which averages performance across a year rather than a single test day. The detailed explanation is on heat pump efficiency: COP, SCOP and SPF.

Why 35°C, 45°C or 55°C flow temperature matters

Heat pumps in the UK are tested and recorded at three flow temperatures: 35°C, 45°C and 55°C. The Product Characteristics Database, used for SAP calculations, records heat pump values at exactly those three temperatures¹⁵.

The default in the standard assessment method is a flow temperature of 55°C¹⁵. But standard, or low temperature, heat pumps are at their most efficient when running at 35 to 45 degrees¹. The reason goes back to the physical rule stated earlier: heat pumps operate more efficiently when the sink temperature is lower. Every degree cooler the system can deliver means less work for the compressor and more heat moved per unit of electricity.

A gas boiler typically runs its radiators far hotter than 55°C. A heat pump designed around 35°C or 45°C therefore asks something different of the home: the emitters, radiators or underfloor loops, must deliver the same warmth using cooler water. That usually means larger radiators or underfloor heating, and it is the main reason a heat pump installation is not just a box swap.

The commissioning certificate for an installation records the design flow water temperature, rounded to the nearest whole number, and the SAP methodology recognises systems designed at 45°C or 35°C as low temperature¹⁵. A household buying a heat pump should expect the installer to state the design flow temperature clearly, because it drives both the efficiency the system will achieve and the emitter work the home needs. The detail is on what flow temperature do heat pumps use for space heating?.

Costs: installation from £8,000 to £15,000, and what it costs to run

The House of Commons Public Accounts Committee reported a wide range in the cost of installing a heat pump, of between £8,000 and £15,000, depending on the work that needed to be done to the home⁴. That range is the honest one to hold onto: the unit itself is only part of the price, and the rest is made up of emitter upgrades, hot water storage, pipework changes and the labour of a two-to-three day installation.

Where a home needs little else done to it, the price sits towards the lower end. Where radiators need replacing, a cylinder needs adding, or the home needs preparatory insulation work, it moves up. Ground source systems cost more again, because the ground array, trenches or boreholes, is a civil engineering job before any heat pump is fitted. Detailed cost breakdowns are on how much does a heat pump cost in the UK? and ground source heat pump cost.

Running costs are where heat pump economics are decided. A household could save as much as 50 per cent and more on running costs with a heat pump compared with a gas boiler, but Which? is careful about the conditions: that requires a high quality installation, high efficiency and a heat pump tariff¹. Those are three separate things, and a household that achieves only one or two of them will see less than the headline saving.

The counterweight is equally firm. Croydon Council's retrofit guidance warns that if a home is not well insulated, installing a heat pump may increase energy bills instead, because electricity is more expensive than gas⁵. This is the single most important caveat in UK heat pump economics: the efficiency ratio must beat the price ratio, or the household loses. The full comparison, including how tariffs change the answer, is on heat pump vs gas boiler running costs and heat pump running costs.

Claiming the £7,500 Boiler Upgrade Scheme grant

The Boiler Upgrade Scheme pays £7,500 towards installing a heat pump. The scheme's own notice of approved grant categories and values confirms the £7,500 grant value¹⁶, and the government announced in 2024 that homeowners in England and Wales can get a £7,500 heat pump grant through the scheme³. Wales promotes the same figure: upgrade your heating with £7,500 off a heat pump¹⁷.

The grant is not paid to the householder as cash. The process works through the installer:

1. Find an installer who is certified under the scheme. Installers must be MCS certified and be certified to install heat pumps and/or biomass boilers¹⁸.
2. Get a quote. The installer applies for the grant on the household's behalf and deducts it from the price.
3. The scheme issues a voucher. For a ground source heat pump the voucher is valid for 6 months¹⁸, reflecting the longer installation time for ground arrays.
4. The installation is completed, commissioned and registered, and the grant is claimed by the installer.

The scheme covers England and Wales. Scotland and Northern Ireland have their own arrangements, covered on heat pump grants and funding across the UK. The scheme's history, including its origin as the Clean Heat Grant, is on the Clean Heat Grant.

Government amendments to the scheme have been made to widen access, set out in the formal government response to consultation¹⁹. What a household actually pays after the grant, worked through with examples, is on how much does a heat pump cost with a Boiler Upgrade Scheme grant?.

What your home needs first: correct sizing, insulation and radiators

A heat pump that is the wrong size for the home is the root cause of most bad experiences. The Building Regulations guidance is blunt about the requirements: heat pump systems must have been sized appropriately, must have adequate controls, and must meet the system requirements set out in the approved document²⁰. Sizing is done by heat loss calculation, room by room, not by rule of thumb.

The information a householder should be handed after installation is specified in the Welsh Approved Document consultation and mirrors good practice across the UK: the operating and maintenance information provided to the dwelling owner should include details of the heat loss calculation, the design flow temperature, competent person scheme confirmation, the size of the emitter circuit and minimum set back temperatures²¹. A householder who receives that pack has the evidence the system was designed rather than guessed.

Insulation comes before the heat pump. Energy Saving Trust advises that topping up wall, floor and loft insulation before installing a heat pump will help reduce its running costs²². This is not a bureaucratic preference: a heat pump running at 35°C or 45°C needs the home to hold the heat it delivers, and a leaky home forces the system to run harder and hotter.

Emitters are the other half of the equation. Because the water is cooler than a boiler's, radiators may need to be larger, or underfloor heating used, to deliver the same warmth. Historically, poor quality installations in UK homes included cases where installers did not size systems correctly, did not upgrade radiators, did not replace narrow bore pipework, or did not properly insulate pipework⁶. Standards have tightened and these issues are much less common now, but they are the failure mode to guard against. The detail is on heat pump sizing and heat loss calculations, radiators, underfloor heating and emitters and can you fit a heat pump without insulating the house first?.

The 1-metre boundary rule, permitted development and planning consent

For most homes in England, an air source heat pump is permitted development, meaning no planning application is needed, provided conditions are met. The rights are contained in Part 14 (Renewable Energy) of The Town and Country Planning (General Permitted Development) (England) Order 2015²³. The legislation's Class G sets the conditions, and the one that has shaped every installation for a decade is the boundary rule: development is not permitted if any part of the heat pump would be installed within 1 metre of the boundary of the curtilage of the dwellinghouse or block of flats²⁴.

That rule is changing. The government announced in June 2025 the removal of the 1m boundary rule, enabling air source heat pumps to be installed within 1m of the property boundary²⁵, and the formal government response to the Boiler Upgrade Scheme consultation confirms amendments to permitted development rights in England which include the removal of the rule that a heat pump must be installed at least 1 metre from the property boundary¹⁹. Until any change takes effect, the rule as legislated still stands, and local guidance such as Cornwall's states plainly that the pump must not be within 1 metre of the curtilage of the property²⁶. Scottish impact assessment material likewise records the requirement that no part of the air source heat pump be within 1 metre of the site boundary²⁷, and Cotswold Council's guidance repeats it for its area²⁸.

The other conditions matter just as much:

• Development is permitted only if the installation complies with the Microgeneration Certification Scheme Planning Standards, MCS 020a²⁹. Where compliance is not achieved, a planning application is required³⁰.
• The volume of the outdoor compressor unit, including housing, must not exceed 1.5 cubic metres on a house, or 0.6 cubic metres on a block of flats²⁹.
• Only the first installation is permitted development on a house which is not detached or a block of flats; on a detached house, the first two are²⁹.
• Installations on pitched roofs are not permitted development; on a flat roof, all parts must be at least one metre from the external edge²⁹.
• Permitted development rights do not apply within the curtilage of a listed building or a scheduled monument²⁹.
• In a conservation area or World Heritage Site, the unit must not be installed on a wall or roof fronting a highway²⁹.
• The system must not be used solely for cooling purposes²⁹.
• Rights may be removed through a planning condition, an Article 4 Direction or other restriction, in which case a full application is needed²⁶.

Wales consulted on changes to its own permitted development rights, with the summary of responses published in December 2025³⁰. Northern Ireland and Scotland have separate regimes, each covered on its own page: planning permission in England, Scotland, Wales and Northern Ireland. Noise sits inside the planning rules: development is permitted only if the installation complies with the Microgeneration Certification Scheme Planning Standards, MCS 020a, explained on MCS 020: the heat pump noise assessment.

Building Regulations, MCS certification and installer competence

The Building Regulations requirements for heat pumps are set out in Approved Document L. All heat pumps should meet Ecodesign product regulations²⁰. The minimum controls are specified: weather compensation or internal temperature control, and a timer or programmer for space heating²⁰. Heat pumps and any dedicated ancillary products, such as integrated hot water storage vessels, should be commissioned in accordance with both the manufacturer's instructions and the appropriate system design parameters²⁰.

Competence is not optional in the regulations. The person carrying out the work should be suitably competent, and the guidance expects the system to have been sized appropriately and to have adequate controls²⁰. In practice that competence is demonstrated through certification: Boiler Upgrade Scheme installers must be MCS certified and certified to install heat pumps¹⁸.

Where the work is carried out by a registered competent person, two paperwork obligations follow. The installer must give a copy of the Building Regulations compliance certificate to the occupier, and must give the certificate, or a copy of the information on it, to the building control authority²⁰. A householder should expect to receive that certificate: it is the record that the installation was notified properly, and it matters later for property sales and grant evidence.

For ground source systems the Welsh consultation adds technical detail worth knowing exists: ground arrays, including header pipes and manifolds, should be flushed as one system to remove all debris and purged to remove all air, a pressure test in accordance with BS EN 805 should be conducted, and commissioning information provided to the dwelling owner should include details of the fluids used and their commissioned concentrations²¹. The wider framework of testing and certification is on heat pump standards, testing and certification.

Smart meters, time-of-use tariffs and keeping your system serviced

Once installed, a heat pump's running cost is largely a matter of when it runs. Access to time-of-use tariffs means cheaper rates during off-peak hours and incentives for energy usage on high-supply days³¹. Because a heat pump is electric and can be scheduled, a household on such a tariff can shift a large share of its heating into the cheap windows, which is the mechanism behind the large savings quoted in the running cost comparison earlier in this guide. A smart meter is the enabler: the tariff needs the meter's half-hourly data to work.

This is also where a heat pump changes a household's relationship with the grid. The home is no longer buying gas at all, which removes one fuel dependence entirely, but it is more exposed to electricity prices and to when electricity is cheap. A household pairing a heat pump with solar panels and a battery can shift that balance further towards independence, a combination considered on should I get solar panels and a battery with my heat pump?.

Servicing is straightforward and cheap compared with the stakes. Energy Saving Trust recommends an annual service for heat pumps²², and its detailed guidance says to get an engineer to service the heat pump according to the manufacturer's advice, usually once a year⁶. The manufacturer's advice is the governing document, because servicing intervals can be a warranty condition, covered on does servicing a heat pump affect the warranty?.

The heat pump itself is likely to last 20 years or more, which is longer than the average gas or oil boiler⁶. The full lifespan picture, including what wears out first, is on what is the lifespan of an air source heat pump?, and day-to-day operation is on heat pump controls, weather compensation and smart operation.

UK heat pump manufacturers and their product lines

The UK market carries a wide range of manufacturers, from global names to specialist British ground source makers. The pages beneath this guide cover each in detail, including Vaillant, Worcester Bosch, Grant, Viessmann, Ideal Heating, Kensa, NIBE, Mitsubishi Ecodan and Daikin Altherma compared, Baxi, Bosch, Panasonic, Thermia, iDM, STIEBEL ELTRON, CTC, Octopus Energy and many more.

One example of what a modern range looks like: the Vaillant aroTHERM Plus, sold in the UK through E.ON Next, is available in output sizes including 3.5kW, 5kW, 7kW, 10kW and 12kW³². It uses a natural refrigerant called R290, which the maker describes as super-friendly to the environment³². On noise, the maker states the range operates quietly, with the exception of the 10kW model, which is slightly louder but still within a comfortable noise range³². Those are the maker's own claims for its own product, and they illustrate the shape of a product range: a spread of outputs to match different heat losses, a refrigerant choice, and a noise profile that varies by model.

Refrigerant choice is becoming a live issue across all brands: self-contained heat pumps up to and including 12kW must not use any F-gases from 1 January 2032, which is pushing the market towards natural refrigerants like R290. That transition is explained on heat pump refrigerants: R290, R32 and the F-gas rules and R290 vs R32 heat pumps.

Heat pumps and the UK's shift from gas boilers

Heat policy in the UK is built around replacing fossil fuel heating, and heat pumps are the designated successor for most homes. Parliament's research briefing states the core finding plainly: heat pumps are technically suitable for most UK homes if installed appropriately². The same briefing identifies the two obstacles: the public's interest in and understanding of heat pumps is low, and reducing the price of electricity relative to gas would make heat pumps more competitive².

The direction of travel is visible in the rules. The government announced the £7,500 grant explicitly to help save households money and deliver cleaner heat to homes³, and the same June 2025 announcement that removed the 1m boundary rule framed it as making installation easier²⁵. Welsh Government guidance encourages households to consider heat pumps as a green energy choice¹⁷, and its essential guide states that heat pumps run on electricity and work efficiently even on cold days, down to temperatures as low as -20°C³³.

For a household, the strategic question is what a heat pump does for independence. It removes the gas pipe, or the oil or LPG delivery, from the home's energy supply. It replaces a fuel that must be burned on site with a machine that multiplies each unit of grid electricity into three or four units of heat. The dependence that remains is the electricity grid and its price structure, which is why tariffs, smart meters and solar-plus-battery combinations sit so close to the heart of the subject. That trade is examined on heat pumps and household energy independence, and the policy timeline on UK heat pump policy, targets and the rules coming.

Limitations: homes with poor insulation and mains gas connections

The limitations are real and worth stating as firmly as the benefits.

• A poorly insulated home can end up worse off. If a home is not well insulated, installing a heat pump may increase energy bills, because electricity is more expensive than gas⁵. The efficiency ratio has to beat the price ratio, and a leaky house undermines it from both directions.
• Mains gas households have the hardest sums. The largest savings, as much as 50 per cent and more on running costs, require a high quality installation, high efficiency and a heat pump tariff¹. A household on a standard tariff with an average installation will see less, and on gas the comparison starts from a cheap fuel.
• Installation quality has been the historic failure mode. Past problems included installers who did not size systems correctly, upgrade radiators, replace narrow bore pipework, or properly insulate pipework. These issues are much less common as standards have tightened⁶, but they are what a bad installation looks like.
• Understanding is thin. The public's interest in and understanding of heat pumps is low², which leaves households exposed to poor advice at the point of purchase.
• Hot water needs storage. Unlike a combi boiler, a heat pump does not provide hot water instantly, so a hot water cylinder is needed⁵. Replacing a combi means finding space for a tank.
• Efficiency drops in very cold weather. Heat pumps can operate effectively at -15 degrees, but their efficiency drops in very cold weather¹, so the coldest weeks cost the most.

None of these is a reason to dismiss the technology; they are the conditions under which it does and does not pay. A well-insulated home, a correctly sized system, emitters suited to low flow temperatures and a tariff that rewards off-peak running are what turn three-to-four units of heat per unit of electricity into a household's advantage. Without them, the same machine underperforms. The honest way to decide is to read the detailed pages beneath this guide, starting with which homes suit a heat pump and how heat pumps actually perform in UK homes.