Ground Source Heat Pumps Explained

A ground source heat pump, also called a ground-to-water heat pump, transfers heat from the ground outside to heat your home and your hot water¹. It does this using lengths of pipe buried in the ground, either in a vertical borehole or a horizontal trench, forming a closed circuit filled with a mixture of water and antifreeze². The heat pump itself sits indoors, and for every unit of electricity it uses, a typical system produces 3 to 4 units of heat², with independent testing figures putting efficiency at 320 to 420%³.

The trade-off is cost and disruption. A ground source installation with the loop buried in trenches is typically around £15,000¹, roughly twice the cost of an air source installation³, and excavation for the ground loop makes it a more disruptive project than an air source fit⁴. Against that, the Boiler Upgrade Scheme currently takes £7,500 off the cost and installation of a ground source heat pump⁵, rising to £9,000 for eligible off-gas-grid properties heated by oil or LPG between 21 July 2026 and 31 March 2027⁶.

Ground source heat pumps explained

A ground source heat pump extracts heat from pipes buried in the ground to heat your home and your water⁹. The ground beneath a garden holds a store of solar energy absorbed over the year, and it stays at a far steadier temperature than the air above it. The heat pump transfers energy from that natural heat stored in the earth to heat the home and domestic hot water¹⁰.

The mechanism is a refrigeration cycle running in reverse. The buried pipe is a closed circuit filled with a thermal transfer fluid, a mixture of water and biodegradable antifreeze known as the brine³. This fluid absorbs heat from the surrounding soil and carries it to the heat pump unit. Inside the unit, an evaporator, a compressor and a condenser work in sequence: the evaporator takes the low-grade heat from the brine into the refrigerant, the compressor raises its temperature, and the condenser transfers that heat to water, which feeds the heating distribution system and the hot water tank². In Northern Ireland's official description, ground source heat pumps make use of heat stored in the ground to pre-heat water for the heating system, and this water is then heated to the required standard using electricity¹¹.

Two points follow from that description. First, the electricity is not the heat source; it is the cost of moving heat from the ground into the house, which is why the output is several times the input. Second, the heat pump feeds a hot water tank rather than delivering hot water on demand, so the system is built around stored hot water². The unit itself is designed for indoor use: domestic ground source and water source heat pumps are self-contained, usually with a footprint of about 600 x 600 mm¹², and you will generally need a space approximately the size of a fridge-freezer, although smaller versions around the size of an under-counter fridge are available for smaller homes⁸.

Choosing between trench collectors and boreholes for your site

The collector, the buried pipe array, comes in two forms: pipes laid in trenches in the ground, or vertical pipes within boreholes¹³. Which one suits a property comes down almost entirely to the land available.

Horizontal systems use lengths of pipe laid in shallow trenches around one to two metres deep⁸. They suit properties with a large enough garden, because the collector has to spread out to gather enough heat. The groundworks are simpler and cheaper than drilling, but the excavated area is significant, and the ground above the loops cannot be built over afterwards.

Boreholes suit properties with little land. The borehole runs somewhere between 75 and 200 metres deep, depending on the size of the system, and it is only about 20 centimetres wide, less than a metre in diameter³. Drilling is more expensive than trenching, but it leaves the garden largely intact and works where a horizontal array simply would not fit. Where a system uses multiple boreholes, separate control of each collector loop is needed¹².

One gap worth knowing about: there are no British Standards specifically for collector loops, nor for the installation of such loops¹². Design and workmanship standards therefore rest on the installer's certification and the contract, which is one reason the choice of installer matters more here than in most heating work. The practical questions to answer with an installer are how much usable land exists, whether the geology suits drilling, and how the collector will be sized against the property's heat demand.

Published efficiency figures range from 320 to 420%

A typical ground source heat pump should be 320 to 420% efficient³. In plainer terms, for every unit of electricity used to pump the heat, 3 to 4 units of heat are produced², and heat pumps generally produce three to four units of heat per unit of electricity they use¹⁴. The percentage expresses the ratio of heat delivered to electricity consumed, which is why the figure can sit above 100%: the electricity is not making the heat, it is moving heat that already exists outdoors into the home.

Why the range? Efficiency depends on the temperature the system has to deliver. A ground source heat pump feeding well-sized emitters at a low flow temperature, such as underfloor heating in a well-insulated home, works closer to the top of the range, because the compressor has less work to do to lift the ground temperature to the delivery temperature. A system pushing heat through small radiators at a higher temperature works harder for the same output.

Ground source systems hold an advantage here over air source because the collector sits in ground whose temperature is stable through the year, rather than in outside air that swings between summer heat and winter cold. Official consultation papers note that ground source systems offer increased energy efficiency relative to air source¹⁵. The efficiency figure is a property of the whole installation, collector, unit, emitters and controls together, not of the box alone, and a poorly sized or badly balanced system will fall short of the published range regardless of what the specification sheet says.

Prices from roughly £15,000 with trenches up to £57,000 for boreholes

Installing a ground source heat pump is typically around £15,000 if your ground loop is buried in trenches¹. That is the headline figure for the cheaper collector option. Borehole systems cost more, because drilling to depths of 75 to 200 metres³ is specialist work, and the total rises with the number of boreholes needed to meet the property's heat demand. Published price ranges for borehole installations run considerably higher than the trench figure, and the overall spread across the market is wide.

What drives the variation? The cost factors are identifiable and worth taking to installers in quotes¹:

• access to the ground, and whether you choose trenches or a borehole to lay the ground loop
• 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
• whether radiator or underfloor heating upgrades are needed at the same time

That last item matters more than many households expect. Because a ground source system works best at lower flow temperatures, existing radiators sized for a gas boiler may need upgrading, and that cost sits inside the project, not beside it. A hot water cylinder is also part of the package for homes that do not already have one⁸.

Against the capital cost, the running economics are favourable: the 3 to 4 units of heat per unit of electricity² means the effective cost of each unit of heat is a fraction of the electricity price. Ground source systems also need less maintenance than combustion boilers, and excavation for the ground loop, while disruptive, offers long-term energy savings⁴. Prices are installer-quoted, and the recommended approach is quotes from at least three MCS-accredited installers before committing¹.

Grants of £7,500, rising to £9,000 off the gas grid

The Boiler Upgrade Scheme (BUS) in England and Wales provides £7,500 off the cost and installation of a ground source heat pump⁵. The government's heat and buildings factsheet describes the scheme as £2.7bn in funding to 2030 to cover £7,500 towards the cost and installation of ground and air source heat pumps, including water source heat pumps¹⁶.

For off-gas-grid homes there is a time-limited uplift. From 21 July 2026, eligible off-gas-grid properties have been able to apply for an uplifted grant of £9,000⁶, and the £9,000 figure applies to air-to-water or ground source heat pumps in eligible off-gas-grid properties, those heated by oil or LPG⁷. The uplifted grant runs until 31 March 2027⁷.

The grant is claimed through the installer, not the householder, which is one reason the installer must be certified under the scheme¹⁸. Once a voucher is issued, the clock starts: vouchers for ground source heat pumps are valid for 6 months¹⁸, a longer window than the 3 months given for air-to-water, air-to-air and biomass vouchers¹⁸, reflecting the groundworks involved. The installation must be completed and the voucher redeemed within that period.

The homes and sites best suited to ground source heat pumps

Heat pumps are best suited to buildings with good insulation levels¹⁹. That single statement shapes most of the suitability question for ground source, because a well-insulated home needs a smaller heat pump, a smaller collector, and lower flow temperatures, all of which reduce both capital cost and running cost. Independent guidance is more specific still: before installing a ground source heat pump, check your home's energy efficiency, and if appropriate add loft and cavity wall insulation first⁸.

The second suitability factor is the heat distribution system. Because the system delivers best at lower flow temperatures, underfloor heating or generously sized radiators suit it well, and undersized emitters force the unit to run hotter and less efficiently. The third factor is hot water: a ground source system works with a hot water cylinder, and heat pumps do not provide hot water instantly, so a cylinder is needed⁴. If you are replacing a combi boiler and do not have a hot water tank, you will need a suitable space to install a new hot water storage cylinder⁸.

The fourth is the house itself. The heat pump unit is installed indoors⁸, so an internal space roughly the size of a fridge-freezer, or an under-counter fridge for the smaller versions, has to exist somewhere⁸. The fifth is the land, as set out above: a garden big enough for trenches, or ground that can be drilled for boreholes. Properties with none of these, no land, no internal plant space, no cylinder position, are better served by other technologies, and an honest installer will say so at survey stage.

Rules on planning, permits and building control

The planning position for ground source heat pumps is unusually favourable. The installation of a ground source heat pump or a water source heat pump on domestic premises is usually considered to be permitted development, not needing an application for planning permission². 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 dwellinghouse²⁰. In England, ground source heat pumps do not usually require planning permission as long as permitted development criteria are met²¹, and the same general position holds for domestic premises elsewhere²². The underlying legislation in Northern Ireland permits the provision of a ground or water source heat pump within the curtilage of a dwellinghouse²³.

The exceptions cluster around protected buildings and areas:

• If the property is listed, installing a ground source heat pump and its associated housing or boxing equipment within the curtilage will need listed building consent²⁴.
• Bristol's guidance for listed buildings is that adding renewable energy solutions like solar panels or air and ground source heat pumps might be acceptable but will require listed and or planning consent²⁵.
• In a conservation area, local requirements can differ, and the advice is to contact your council to check²⁶.

Building regulations apply regardless of the planning position. Installation of either a ground source or an air source heat pump will have to comply with the Building Regulations²⁷, and the relevant building regulations requirements are the same for ground source heat pumps as for air source⁴. The approved document guidance expects commissioning information for the owner to include details of the fluids used and their commissioned concentrations²⁸, which is the householder's record of what is in the ground loop and at what strength.

Getting it fitted: surveys, digging and approved installers

Installing a ground source heat pump is not a DIY job⁸. Sizing, design and installation should be done by a suitably qualified professional, and the specific recommendation is to look for a Microgeneration Certification Scheme (MCS) certified installer⁸. MCS certification matters twice over: it is the quality gate for the installation, and it is the route through which the Boiler Upgrade Scheme grant is accessed, since the scheme is administered through certified installers¹⁸.

The process runs in a clear order:

1. Efficiency check first. Check the home's energy efficiency and add loft and cavity wall insulation if appropriate⁸.
2. Survey and design. The installer assesses the property's heat demand, the land available, and whether trenches or a borehole suit the site¹.
3. Quotes. Get quotes from at least three different MCS-accredited installers¹.
4. Groundworks. Excavation is needed for installing the ground loop system⁴. This is the disruptive stage: trenches are dug to one to two metres deep⁸, or a borehole is drilled to between 75 and 200 metres³. Council guidance rates the disruption level for ground source installation as high⁴.
5. Heat pump fitting. The installation of the ground source heat pump itself typically takes one to two days for a professional installer to complete⁸.
6. Commissioning and handover. The system is commissioned, and the owner should receive details of the fluids used and their commissioned concentrations²⁸.

The one to two days of heat pump fitting⁸ is therefore the smallest part of the timeline. The survey, quoting, groundworks and commissioning stretch the project well beyond that, and households planning around the six-month voucher window¹⁸ should build that wider timeline into their plans rather than the fitting time alone.

Is a ground source pump worth the premium over air source?

A ground source heat pump costs around twice as much as an air source heat pump installation³. An air source heat pump is easier and cheaper to install than a ground source heat pump because it does not use buried pipes²⁹, and official consultation papers note that ground source systems are typically more expensive and require more space¹⁵. For many homes, that ends the comparison: if the budget or the land is not there, air source delivers most of the benefit of electrified heating at a fraction of the installation burden.

What the extra money buys is threefold. First, efficiency: ground source systems offer increased energy efficiency¹⁵, because the collector sits in ground at a stable temperature rather than in outside air, so the compressor does less work, particularly in winter when heat is needed most. Second, quiet: ground source systems are quieter¹⁵, with no large external fan unit, which matters on tight sites and with neighbours. Third, the collector itself is out of sight and out of the weather, with no external unit needing siting and clearances.

The counterweights are real. Ground source needs land for the collector or ground that can be drilled¹³, the disruption during installation is rated high⁴, and the capital cost is roughly double³. Air source awareness among owner-occupiers stands at 84% against 78% for ground source⁹, and the two technologies are not substitutes in every property: a flat with no garden cannot host a ground loop at all, while a home with land and a long-term view can.

How a ground source heat pump affects your energy self reliance

A ground source heat pump removes the fossil fuel supply from a home's heating: no gas pipe, no oil delivery, no LPG tank. The heat source is the ground under the property, a store that does not run out, does not arrive by tanker, and is not exposed to fuel price movements. Against that, the system runs on electricity, so the household remains connected to the grid and exposed to electricity prices, though the 3 to 4 units of heat per unit of electricity² softens that exposure considerably. The remaining dependencies are the installer and the equipment maker for servicing and parts, and the scheme administrator for the grant.

Ownership in the UK is still rare. In the Summer 2025 official attitudes tracker, only a very small proportion of owner occupiers said they had already installed a ground source heat pump, at 1%⁹. Awareness is high, at 78% among owner-occupied households⁹, but the step from awareness to installation is where the cost, the land requirement and the disruption⁴ bite. Overall likelihood to install or already have a ground source heat pump among owner-occupiers moved from 18% to 14% over the tracker's reporting period⁹.

For a household weighing the investment, the independence case rests on durable facts: a collector buried in the ground working at 320 to 420% efficiency³, a grant of £7,500 or £9,000 off the capital cost⁵, a system quieter than its air source counterpart¹⁵, and a heat source that no supplier controls. The dependence that remains is the electricity supply, and the honest summary is that ground source shifts a home from fuel dependence to grid dependence, a shorter and more manageable chain, but not a complete break.