The short answer
A ground source heat pump (GSHP) extracts heat from the ground rather than the air. A network of buried pipes — the ground loop — circulates a water-and-antifreeze mixture that absorbs the steady, mild heat held in the soil or in rock a few metres down. That collected heat is passed to the heat pump, where a refrigerant cycle upgrades it to a useful temperature for your radiators, underfloor heating and hot water cylinder. Because ground temperature stays relatively constant year-round — typically around 8 to 12 °C in the UK — a GSHP often achieves a slightly higher and more stable efficiency (SCOP) than an air source unit, especially in deep winter. The trade-off is a more disruptive and costly installation, because it needs either long horizontal trenches or deep vertical boreholes.
Ground source heat pumps are less common in the UK than air source units, mainly because of the groundworks involved. But for homes with the land or budget, the stable ground temperature can deliver consistently strong efficiency. Understanding the ground loop is the key to understanding the system.
Ground source heat pump key facts
- Heat sourceThe ground (soil or rock)
- Ground temperatureRoughly 8 to 12 °C year-round
- Collector typesHorizontal trenches or vertical boreholes
- Typical efficiency (SCOP)Often around 3.5 to 4.5
- Main drawbackDisruptive, higher-cost groundworks
How a ground source heat pump works
A GSHP has two linked circuits. The first is the ground loop: buried pipe filled with a water-and-antifreeze fluid (often called brine) that circulates underground and absorbs the earth's natural heat. The second is the refrigerant circuit inside the heat pump unit, which works exactly like an air source pump:
- The mild heat collected by the ground loop boils a refrigerant into a gas.
- A compressor raises the gas temperature.
- A heat exchanger transfers that heat to your heating water and hot water cylinder.
- The refrigerant condenses, expands, cools, and the cycle repeats.
The advantage over air source is the source temperature. Outside air can drop below freezing on a cold night, but the ground a metre or two down stays mild all year. A warmer, more stable source means the pump works less hard to reach the target flow temperature, which supports a steady efficiency.
Horizontal loops vs boreholes
The ground loop can be installed in two ways, and which one you need depends on how much land you have:
- Horizontal ground loops: pipe laid in trenches roughly 1 to 2 metres deep across a garden or field. Cheaper to dig, but they need a substantial area of open land.
- Vertical boreholes: one or more holes drilled deep into the ground, with pipe inserted as a loop. They take up little surface area, making them suitable for smaller plots, but drilling is more specialised and expensive.
Both options are sized to the home's heat demand, and getting that sizing right is essential — an undersized loop can cool the ground over a heating season and lose efficiency.
| Collector type | Land needed | Relative cost | Best suited to |
|---|---|---|---|
| Horizontal trenches | Large garden or field | Lower | Rural / large plots |
| Vertical boreholes | Small footprint | Higher | Smaller plots / restricted sites |
Indicative comparison of ground loop types. Sources: Energy Saving Trust; MCS.
How it compares to an air source heat pump
Both pump types use the same refrigerant principle and deliver low-temperature heat to a wet system. The differences are about the heat source and the installation:
- Efficiency: A GSHP commonly achieves a SCOP of around 3.5 to 4.5, often a little higher and more consistent than an ASHP because the ground stays warmer than winter air.
- Installation: A GSHP needs trenching or drilling, making it more disruptive and significantly more expensive to install than an ASHP.
- Appearance and noise: There is no outdoor fan unit, so a GSHP is silent outside and visually discreet once the groundworks are complete.
For most UK homes the lower installation cost of an air source unit wins. A ground source pump tends to make sense where there is suitable land, a high heat demand, or a desire for the steadiest possible winter efficiency.
The way to weigh the two is to separate the running benefit from the upfront cost. A ground source system's steadier source temperature means it avoids the efficiency dip an air source unit suffers on the coldest nights, and it has no outdoor fan to defrost, so it tends to hold a higher SCOP precisely when heat demand peaks. Over a long winter that can translate into lower electricity use. But the groundworks — trenching or borehole drilling — add several thousand pounds and real disruption that an air source unit, which simply mounts outside, avoids entirely. For a typical well-insulated home the running-cost saving rarely repays that gap quickly, which is why air source is the default. Ground source comes into its own for larger or off-gas properties with high heat demand, sites where outdoor noise or appearance rules out a fan unit, or developments installing several pumps at once where shared boreholes spread the drilling cost.
Cost, grants and what installation involves
The defining feature of a ground source installation is the groundworks. Before the pump is connected, an installer must either dig trenches across a garden or bring in a rig to drill boreholes. This is what makes a GSHP significantly more expensive to install than an air source unit, and why it is far less common in the UK despite its strong efficiency.
The process typically runs in stages:
- Survey and design: an MCS heat loss survey establishes the home's peak heat demand, which sizes both the pump and the length of ground loop required.
- Groundworks: trenching or borehole drilling, then laying and connecting the loop. This is the disruptive phase, after which the garden is reinstated.
- Indoor connection: the heat pump unit, hot water cylinder and controls are installed and connected to the existing radiators or underfloor heating.
- Commissioning: the system is filled, balanced and tuned to run at a low flow temperature for best efficiency.
On cost support, a ground source heat pump qualifies for the same £7,500 Boiler Upgrade Scheme grant in England and Wales as an air source unit, provided the installer and installation are MCS certified. Because the upfront cost is higher, that grant covers a smaller share of the total — but the long ground-loop lifespan and steady efficiency are what make the investment worthwhile over decades for suitable properties. As with any heat pump, good insulation and correctly sized emitters are essential to realise the efficiency the ground source promises.
Frequently asked questions
Do I need a big garden for a ground source heat pump?
For horizontal trench loops, yes — you need a substantial area of open land. If space is limited, vertical boreholes drilled deep into the ground take up a small surface footprint instead, though they cost more to install. A surveyor sizes the loop to your home's heat demand and confirms what your plot can accommodate.
Is a ground source heat pump more efficient than air source?
Often slightly, and more consistently. Because ground temperature stays mild all year while winter air can fall below freezing, a GSHP typically holds a steadier efficiency through the coldest months. The gap is modest, and the much higher installation cost means air source is the more common choice for UK homes.
Does a ground source heat pump qualify for the Boiler Upgrade Scheme?
Yes. Ground source heat pumps are eligible for the Boiler Upgrade Scheme grant in England and Wales, the same as air source heat pumps, provided the installation and installer are MCS certified and other scheme conditions are met. The grant helps offset the higher upfront groundworks cost.
Sources & further reading
- Energy Saving Trust — Ground source heat pumps
- MCS — Heat pumps for consumers
- gov.uk — Boiler Upgrade Scheme
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.