What a ground source system is
A few metres below the surface, the ground holds a remarkably steady temperature all year — warmer than the air on a January morning and cooler than it in August. A ground source heat pump exploits that.
Fluid circulates through a sealed loop of buried pipework, absorbing low-grade heat from the surrounding ground. Indoors, the heat pump lifts that heat to a useful temperature and passes it into your heating water, exactly as an air-to-water system does. From inside the house, the two behave the same way: radiators, underfloor heating and a hot water cylinder.
The difference is entirely outside, and it is the difference that decides whether the project is feasible.
Ground arrays: the three ways heat is collected
The two common collectors are drawn below. Both end up doing the same thing indoors — the difference is entirely in what has to happen to your land to get there.
Horizontal loops
Pipework laid in shallow trenches, straight or coiled, across an area of open ground. The digging is not deep, but it covers a lot of land — which is why this suits paddocks and large rural plots rather than a domestic garden.
Vertical boreholes
Narrow bores drilled to considerable depth, taking a very small surface footprint. They reach ground that stays warmer through winter, but a drilling rig has to be able to physically reach the position — which is what rules them out on most tight sites.
| Array type | What it is | What the site needs | Notes |
|---|---|---|---|
| Horizontal loops (slinky or straight) | Trenches at shallow depth across an area of ground | A large area of accessible open land | Lower drilling cost; the ground is dug and reinstated |
| Vertical boreholes | Deep, narrow bores taking a small surface footprint | Rig access to the site and suitable geology | Steadier ground temperature; far less land used |
| Water source (where it qualifies) | Heat taken from a suitable body of water | A watercourse or lake, plus the relevant consents | Treated within the same grant category as ground source |
Horizontal loops
Pipework is laid in trenches at shallow depth across an area of ground, either in straight runs or in coiled "slinky" form to fit more pipe into a shorter trench. The excavation is substantial but shallow, and the ground is reinstated afterwards.
The trade-off is area. Horizontal collection needs a lot of land relative to the heat it provides, which is why it suits farms, paddocks and large rural plots rather than domestic gardens.
Vertical boreholes
Boreholes are drilled to considerable depth and take a very small surface footprint — a practical answer where land is limited. They reach ground that is warmer and more thermally stable than the shallow layers, which helps winter performance.
The constraints are access and geology. A drilling rig has to physically reach the position, and what lies underneath affects both the drilling and the number of bores needed. Boreholes are the more expensive route.
Water source
Where a suitable body of water is available, heat can be collected from it instead. Qualifying water-source systems sit within the same grant category as ground source under the Boiler Upgrade Scheme. The consents involved make this a specialist case rather than a general option.
Site considerations that decide it
- Available land, or rig access. One or the other has to work. This is the question that ends most enquiries, and it is worth asking first.
- What is already buried. Drainage, services, septic systems and old foundations all constrain where an array can go.
- Ground conditions. Soil type and geology affect how much heat the ground will give up and therefore how much pipework or how many bores are needed.
- Consents. Requirements vary with the property and the works, particularly for boreholes. Establish this at survey.
- Reinstatement. With horizontal loops, the state the ground is left in — and who is putting it back — should be written into the quotation, not assumed.
Which properties suit ground source
The technology makes most sense where three things line up: a high annual heat demand, a site that can physically take an array, and an owner with a long time horizon. Large rural houses, farm properties, converted buildings and small multi-building schemes are the classic fit.
It is a weaker fit for a compact modern house on a small plot — not because it would not work, but because the groundworks cost the same regardless of how little heat you need, so the arithmetic rarely rewards it.
If the site rules ground source out, air source does the same job for the house with a far smaller project attached. Our guide comparing air source and ground source sets the two out side by side.
What installation involves
- Survey. A room-by-room heat loss calculation for the building, plus a site assessment for the array — land, access, services and ground conditions.
- Design. Heat pump size, array type and size, flow temperature, emitter schedule and cylinder.
- Groundworks. Trenching or drilling, laying the collector, and connecting it to the building. This is the stage that makes the project longer than an air source one.
- Indoor installation. Heat pump, cylinder, any radiator changes, controls and electrical work.
- Commissioning and reinstatement. Setting the system up to run at its design temperature, and putting the ground back.
We do not publish installation prices for ground source systems. The groundworks are the largest variable and they are genuinely site-specific — a figure quoted without seeing the site would be a guess dressed up as information.
Grant support
In England and Wales, an eligible ground source heat pump installation currently attracts £7,500 under the Boiler Upgrade Scheme — the same value as an air-to-water system, so the grant does not favour one technology over the other.
Properties off the mains gas grid replacing oil or LPG heating may instead qualify for £9,000, available until 31 March 2027. Rural properties with land are exactly the profile where both the technology and that higher value tend to line up, which is worth knowing before the deadline. See the off-gas-grid heat pump grant page for the conditions.
Grant values are not quotations
The grant is a fixed contribution towards the installation, not a proportion of it. On a ground source project the groundworks are a substantial part of the total, so the balance you pay is more variable than for an air source system.