Ground Source Heat Pumps Explained

A ground source heat pump, also called a ground-to-water heat pump, moves heat from the ground outside into the house¹. Lengths of pipe are buried in a borehole or a horizontal trench, usually as a closed circuit filled with a mixture of water and antifreeze, and the heat pump, working through an evaporator, a compressor and a condenser, raises that low grade heat and transfers it to a hot water tank which feeds the heating distribution system². It provides both space heating and domestic hot water³.

Performance is the reason households consider it. A typical ground source heat pump is described as 320 to 420% efficient, generating 3.5 to 4.5 units of heat for each unit of electricity used. Official planning guidance puts the figure at 3 to 4 units of heat per unit of electricity². The price of that performance is groundworks. Published UK installation figures range from around £15,000 where the ground loop is buried in trenches to around £57,000 where a borehole must be drilled¹, roughly twice the cost of an air source installation.

Grant support narrows the gap. The Boiler Upgrade Scheme offers £7,500 off the cost and installation of a ground source heat pump in England and Wales, and since 21 July 2026 an uplifted grant of £9,000 for air-to-water or ground source heat pumps in eligible off-gas grid properties, available until 31 March 2027⁵. Uptake remains small: in Summer 2025, 78% of owner-occupiers said they were aware of ground source heat pumps, but only 1% had one installed⁸.

What a ground source heat pump is and how it works

The ground a metre or more below a garden holds heat through the year. A ground source heat pump transfers energy from that natural heat stored in the earth to heat the home and domestic hot water⁹. Guidance for Northern Ireland describes the sequence plainly: the system uses heat stored in the ground to pre-heat water for the heating system, and this water is then heated to the required standard using electricity¹⁰.

The circuit has two halves. Outside, a buried loop of pipe carries thermal transfer fluid, a mixture of water and biodegradable antifreeze known as the brine. The brine absorbs heat from the ground and passes it through a heat exchanger into the heat pump¹¹. Inside, the refrigerant circuit does the upgrading: an evaporator takes heat from the brine, a compressor raises its temperature, and a condenser gives that heat to the water in the hot water tank and the heating system². Because the process moves existing heat rather than burning fuel, the heat output is higher than the electricity input, around 1kW of electricity for 4kW of heat generated¹².

The unit itself lives indoors. Heat pumps for domestic ground and water source systems are self-contained, generally designed for indoor use, usually with a footprint of about 600 x 600 mm¹³. In practice that means finding space roughly the size of a fridge-freezer, though smaller versions around the size of an under-counter fridge are available for smaller homes. There is no outdoor fan box, which is the visible difference from an air source heat pump.

Heat is delivered at a lower temperature than other forms of heating, which is why the system pairs naturally with underfloor heating and larger emitters.

Horizontal loops or boreholes: which collector suits your land

There are two ways to get the pipe into the ground: pipes laid in trenches, or vertical pipes within boreholes¹⁴. The choice is usually decided by how much land there is, not by preference.

Horizontal collectors are used when there is a lot of land, and the pipe is generally laid out in long straight runs¹⁵. Trenches are shallow, around one to two metres deep, or roughly two metres in depth¹⁶. Excavation is needed for the ground loop system¹⁷, and the area disturbed is substantial, which is why significant outdoor space is listed as the main disadvantage of the technology³.

Vertical collectors suit smaller gardens. A borehole is only about 20cm wide, and somewhere between 75 and 200 metres deep. Other UK figures put domestic boreholes at around 75 to 100 metres¹⁵ and at 90 to 160 metres¹², and drilling to 200 metres is possible depending on system size, though the bore remains less than a metre in diameter. Vertical collectors are described as more efficient, and also more expensive¹⁵. Where several boreholes are drilled for one property, separate control of each collector loop is needed¹³.

One point householders rarely hear: there are no British Standards specifically for collector loops, nor for the installation of such loops¹³. Design quality therefore rests on the competence of the installer and on scheme certification rather than on a single national loop standard. The detail of loop design, spacing and ground conditions is covered under ground loops and boreholes, and shared arrays across several dwellings under shared ground loop networks.

Efficiency: 320 to 420% in the published figures

The coefficient of performance is the ratio of heat delivered to electricity consumed. For ground source, published UK figures cluster between 3 and 4.5. Which? states a typical ground source heat pump should be 320 to 420% efficient, and that it can generate 3.5 to 4.5 units of heat for each unit of electricity, using 4.0 in its own worked example. The Planning Portal gives 3 to 4 units of heat per unit of electricity², the Chartered Institute of Plumbing and Heating Engineering gives around 1kW of electricity per 4kW of heat¹², and Nesta describes ground source systems as providing 3 to 4 times the amount of heat as the electricity they use³. The Energy Saving Trust's general heat pump figure is three to four times as much heat, 300 to 400%⁴.

The documents differ at the edges rather than in substance: the spread reflects different assumptions about flow temperature, ground conditions and whether a seasonal or an instantaneous figure is being quoted. For comparison, an air source heat pump is put at around 1kW of electricity per 3 to 4kW of heat¹², and a typical heat pump of any type at 2.5 to 4.5 units of heat per unit of energy¹⁸.

Ground source scores higher for a physical reason. Deep ground temperature is relatively stable through the year, so the pump is not fighting a cold outdoor air temperature on the coldest days, which is also why ground source models can be more reliable¹¹. Ground conditions still matter: efficiency is described as generally higher than air source but dependent on ground conditions¹⁹.

Flow temperature is the other lever. The mechanics of COP, SCOP and SPF are set out under heat pump efficiency.

Cost: from around £15,000 for trenches to £57,000 for a borehole

There is no published list price for a ground source heat pump: the figures below are whole installations, quoted by installers after survey, and they vary more than for any other domestic heating technology.

These figures are not all the same measurement. The £15,000 figure is a typical trench installation; the £24,000 to £49,000 band is sized by property; the £28,000 to £57,000 band spans both collector types. Taken together they set a floor around £15,000 and a ceiling around £57,000, with drilling the single largest swing factor.

The Energy Saving Trust lists the drivers: access to the ground and whether trenches or a borehole are used, the brand, model and size of heat pump, the size of the property and its heat need, whether it is a new build or an existing property, and whether radiators need upgrading or underfloor heating installing¹. Getting quotes from at least three certified installers is the recommended approach¹. Fuller treatment of prices sits on ground source heat pump cost and how much a heat pump costs.

The Boiler Upgrade Scheme: £7,500, or £9,000 off the gas grid

The Boiler Upgrade Scheme gives £7,500 off the cost and installation of a ground source heat pump⁶. The wider government commitment behind it is £2.7bn in funding to 2030 covering £7,500 towards the cost and installation of ground and air source heat pumps, including water source heat pumps²¹.

From 21 July 2026, eligible off-gas grid properties can apply for an uplifted grant of £9,000 for an air-to-water or ground source heat pump⁵. The uplift targets off-grid properties heated by LPG or oil²², and it runs until 31 March 2027⁷. Two grant values therefore apply at once, £7,500 as the standard rate and £9,000 where the off-gas-grid conditions are met, and the guidance documents present both.

Voucher validity differs by technology, and ground source gets the longer window because of the groundworks:

• Ground source heat pump vouchers are valid for 6 months from issue²³.
• Air-to-water, air-to-air and biomass boiler vouchers are valid for 3 months²⁵.

The grant is claimed through a certified installer, who may apply on the householder's behalf. The Boiler Upgrade Scheme covers England and Wales; support elsewhere differs, and the national picture is set out under heat pump grants across the UK.

Where a ground source heat pump fits best

Because the heat is delivered at a low temperature, the fabric of the house does much of the work. Ground source systems are better suited to well-insulated homes with thorough draught-proofing in place¹⁶, and official guidance states that heat pumps are best suited to buildings with good insulation levels, with insulation added internally or externally where a home does not already have it²⁷. Checking the home's energy efficiency and, if appropriate, adding loft and cavity wall insulation before installing is the standard sequence. MCS takes a broader view, saying heat pumps can work in all types of homes, including those that have less insulation²⁸; the two positions are about cost and comfort at a given flow temperature rather than about whether the machine functions.

Emitters matter as much as insulation. Ground source heating is most effective with underfloor or air heating systems¹⁶, and works best with underfloor heating, which requires lower flow temperatures than radiators. Where existing radiators are retained, sizing has to be checked, which is where heat pump sizing and heat loss calculations come in.

Hot water needs storage. Unlike combi boilers, heat pumps do not provide hot water instantly, so a hot water cylinder is needed²⁹. A household replacing a combi boiler with no existing tank will need suitable space for a new hot water storage cylinder³⁰, in addition to the fridge-freezer sized space for the heat pump. Options are compared under hot water cylinders for heat pumps.

Nesta places the technology as mostly suited to large homes with lots of outdoor space, supported by the Boiler Upgrade Scheme³. That is the honest summary: land, insulation and cylinder space are the three gates.

Planning permission, permits and building regulations

In most cases no planning application is needed. The installation of a ground source heat pump or a water source heat pump on domestic premises is usually considered to be permitted development³¹. In Wales, permitted development rights permit the installation, alteration or replacement of a ground source heat pump or water source heat pump within the curtilage of a dwellinghouse³². In Northern Ireland the equivalent right, Part 2 Class F, covers the provision of a ground or water source heat pump within the curtilage of a dwellinghouse³³. Councils in England describe the same position, covering installation, alteration or replacement of a microgeneration ground source heat pump within the curtilage of a dwellinghouse or a block of flats³⁴, and confirm that installation within the curtilage of a house or block of flats does not require planning permission²⁷.

The exceptions are heritage. Installing a ground source heat pump within a conservation area property's curtilage is permitted development, but installing one and its associated housing or boxing equipment within the curtilage of a listed building will need listed building consent³⁵. Renewable energy solutions on listed buildings might be acceptable but will require listed and or planning consent³⁶. Guidance for listed buildings and conservation areas is consistent that the council should be contacted to check local requirements³¹. Note the contrast with air source: on a listed building, both planning permission and listed building consent are typically needed for an outdoor air source unit²⁷. Nation by nation detail is on the planning pages for England, Scotland, Wales and Northern Ireland.

Permitted development is not an exemption from building control. Installation of either a ground source or air source heat pump will have to comply with the Building Regulations³⁷, and the relevant requirements are the same for ground source as for air source²⁹. Approved Document L expects the information handed to the owner for a ground source installation to include details of the fluids used and their commissioned concentrations²⁶.

Installation: survey, groundworks and certified installers

The sequence begins with assessment, not with digging. A certified contractor will assess the home's heating requirements before proposing the most suitable heat pump size and model, and may apply for a government grant on the householder's behalf. The Energy Saving Trust recommends quotes from at least three installers accredited through the Microgeneration Certification Scheme¹, and certified installers use MCS certified ground and water source heat pumps, meaning the product has been tested for quality, reliability and performance²⁸.

1. Survey and heat loss assessment, sizing and system design.
2. Ground assessment and choice of trench or borehole; grant voucher application where applicable.
3. Groundworks: excavation for trenches, or drilling for boreholes, and laying the collector loop.
4. Indoor work: heat pump unit, cylinder, emitter changes, electrical connection.
5. Commissioning, including recording the fluids used and their concentrations²⁶, and handover.

Fitting the heat pump itself typically takes one to two days for a professional installer. The groundworks sit outside that figure, and disruption during installation is rated high²⁹. Installing a ground source heat pump is not a DIY job. The 6 month voucher validity for ground source under the Boiler Upgrade Scheme²³ is a reasonable guide to the outer span of a project from voucher to completion. The process in general is described under heat pump installation.

Ground source versus air source: what the extra cost buys

The trade is consistent across every source: ground source costs more to install and performs better once running.

Ground source gives lower running costs and lower CO2 emissions, but costs more to install³⁹. It is usually more efficient than an air source heat pump but more expensive to install³⁰, and higher set-up costs are the recognised trade against generally higher efficiency¹⁹. Ground source also requires more outdoor work to install³⁸.

Where the extra spend tells is on fuel displaced and on weather. A ground source unit will save much more money if it is replacing an electric or coal-based system, and may not be suitable where the home is on mains gas¹⁶; that judgement is about the price of the fuel being replaced, not about the machine. Stable underground temperatures are the performance argument, addressed further under ground source versus air source in cold weather. For households without the land, air-to-water heat pumps do the same job from outdoor air.

What owning one means for household energy independence

A ground source heat pump changes what a household depends on, it does not remove dependence. Gas, oil or LPG deliveries go, and with them the exposure to those fuel markets. In their place, the home depends entirely on mains electricity: the compressor and circulation pumps stop when the supply does, and there is no fuel stored on site. The heat, though, is local and permanent, drawn from the ground under the property, with the electricity used only to upgrade it, three to four units of heat for every unit drawn from the grid⁴³.

The ground array is the most durable part of the asset. Long life expectancy is listed as an advantage of individual ground source systems³, and once a borehole is drilled or trenches backfilled, that infrastructure belongs to the property. The dependence that remains is on the manufacturer for the indoor unit, its refrigerant circuit and its spares, on a certified installer for servicing, and on the grid for every kilowatt-hour consumed. Pairing with on-site generation shifts part of that, and the interaction is covered under heat pumps and household energy independence.

Metering is worth noting: under the Domestic Renewable Heat Incentive, an air source or ground source heat pump had to be metered for the householder to receive scheme payments⁴⁴, a reminder that grant and incentive schemes attach conditions to the equipment as well as to the installer.

Adoption is still thin on the ground. In Summer 2025, 78% of owner-occupiers were aware of ground source heat pumps against 84% for air source, and only 1% of owner-occupiers had already installed one⁸. Stated likelihood to install or already have a ground source heat pump was reported at 18% and at 14% across the periods covered, and the published figures differ on that point⁸. For most UK households the barrier is not the technology but the land and the capital: significant outdoor space³ and an installed cost that starts around £15,000 and can reach around £57,000¹, against a grant of £7,500 or £9,000⁶.