The short answer
An air source heat pump (ASHP) takes heat from the outside air, while a ground source heat pump (GSHP) takes it from buried pipework in the ground. Both use the same refrigerant principle and feed a wet heating system, but they differ in three ways that matter. Efficiency: a GSHP is usually a little more efficient and more stable in deep winter because the ground stays warmer than cold air. Cost and disruption: an ASHP is much cheaper and simpler to install, whereas a GSHP needs trenches or boreholes, raising cost substantially. Space: an ASHP only needs a spot outside for the unit, while a GSHP needs land for trenches or room to drill. For most UK homes the lower installed cost makes air source the default choice; ground source suits properties with land, high heat demand, or a priority on top efficiency.
The two heat pump types share the same basic technology, so the decision comes down to your property, budget and tolerance for groundworks. This page lays the differences side by side so you can see which fits.
Quick comparison
- Air source heat sourceOutside air
- Ground source heat sourceThe ground (soil or rock)
- Air source efficiency (SCOP)Around 3.0 to 4.0
- Ground source efficiency (SCOP)Around 3.5 to 4.5
- Air source installCheaper, less disruptive
What the two systems share
Before the differences, it helps to be clear on what air source and ground source heat pumps have in common, because it is most of the system. Both:
- Use a refrigerant cycle to absorb low-grade heat and upgrade it to a useful temperature, the same principle that runs a refrigerator in reverse.
- Deliver heat at a lower flow temperature than a gas boiler, so both rely on correctly sized radiators or underfloor heating and good insulation to perform.
- Heat your domestic hot water via a cylinder, replacing the role of a combi or system boiler.
- Run on electricity rather than burning fuel on site, so both cut carbon emissions at the point of use.
- Qualify for the same £7,500 Boiler Upgrade Scheme grant in England and Wales when MCS certified.
Because the indoor side is so similar, the real decision is about the heat source and the groundworks — and that is where cost, efficiency and disruption diverge.
The core difference: where the heat comes from
Both systems work on the same principle — a refrigerant absorbs low-grade heat, a compressor upgrades it, and the heat is released into your radiators, underfloor heating and hot water cylinder. The difference is the heat source:
- An air source heat pump uses an outdoor fan unit to draw heat from the air. Air temperature swings with the weather, so efficiency dips on the coldest days.
- A ground source heat pump circulates fluid through buried pipes to collect heat from the ground, which stays a mild 8 to 12 °C all year. That stable source gives a steadier winter performance.
This single difference drives almost every other distinction between the two systems. The ground is a far more generous heat source in winter than the air precisely because it does not get cold when the weather does. A metre or two down, soil holds onto warmth absorbed over the summer, so a ground source pump faces a gentle, stable temperature even during a January cold snap — the time a home needs the most heat. An air source pump must work hardest exactly when the air it draws from is at its coldest, which is why its seasonal efficiency is typically a little lower and why it occasionally pauses to defrost. Neither effect stops an air source pump heating a UK home well; it simply means the ground source version trades a higher up-front cost for steadier, slightly cheaper running.
Cost, space and disruption
The biggest practical gap is installation. An ASHP is essentially an outdoor unit plumbed into your heating, so the work is comparable to a complex boiler swap. A GSHP needs significant groundworks — either long horizontal trenches across a garden, or vertical boreholes drilled deep — before the pump itself is even connected.
That makes a GSHP considerably more expensive to install and far more disruptive to your garden. It also needs either a large plot for trenches or access for a drilling rig. An ASHP, by contrast, needs only a suitable outdoor location for the unit and usually qualifies for permitted development if siting rules are met.
Space and property type therefore decide a great deal. A detached home with a large garden has the room for trenches and can realistically consider ground source; a terraced house or a flat with no land of its own usually cannot, leaving air source as the practical option. Boreholes can sidestep a lack of horizontal space, but drilling adds cost and needs rig access. The trade-off is rarely about which technology is better in the abstract — both are mature and effective — and almost always about whether the groundworks a ground source system demands are feasible and worth the extra outlay for your particular plot. For the large majority of UK homes, air source ends up being the chosen route simply because it asks far less of the site, while ground source makes most sense for larger rural or new-build properties where the groundworks can be done efficiently.
| Factor | Air source (ASHP) | Ground source (GSHP) |
|---|---|---|
| Heat source | Outside air | The ground |
| Typical efficiency (SCOP) | 3.0–4.0 | 3.5–4.5 |
| Winter consistency | Dips on coldest days | More stable |
| Install cost | Lower | Higher |
| Disruption | Low | High (trenches / boreholes) |
| Space needed | Outdoor unit spot | Land or drilling access |
| Outdoor noise | Low fan hum | Silent (no fan) |
Indicative comparison for guidance only. Sources: Energy Saving Trust; MCS.
Which one suits your home?
As a general guide:
- Air source suits most UK homes. It is cheaper, quicker and less disruptive, and modern units perform well through a normal British winter. It is the most common choice and the one most installers fit.
- Ground source suits properties with land or high demand. If you have a large garden or budget for boreholes, a high heat load (a big or older property), or you want the steadiest possible winter efficiency, the ground loop can repay the extra cost over many years.
For either type, the same fundamentals decide success: correctly sized emitters (radiators or underfloor heating), good insulation, and a low flow temperature. A poorly designed system of either type will disappoint, while a well-designed one will heat the home comfortably and efficiently.
Frequently asked questions
Is ground source always more efficient than air source?
On average yes, and more consistently through winter, because the ground stays warmer than cold air. But the gap is modest — a well-designed air source system at a low flow temperature can perform very well. The much lower installation cost of air source usually outweighs the efficiency advantage of ground source for typical homes.
Which is cheaper to install, air source or ground source?
Air source is substantially cheaper because it avoids groundworks. A ground source system needs trenches or boreholes dug before the pump is connected, which adds significant cost and disruption. Both qualify for the same £7,500 Boiler Upgrade Scheme grant, which reduces the upfront difference but does not eliminate it.
Can I switch from air source to ground source later?
In practice this is rarely done because it means installing a whole new ground loop — the expensive part. It is more sensible to choose the right system at the outset based on your land, budget and heat demand. Most homeowners weighing the two settle on air source unless they have a specific reason to invest in ground source groundworks.
Sources & further reading
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.