Air Source vs Ground Source Heat Pumps
How air source and ground source heat pumps differ in efficiency, installation, running costs and site requirements — and which suits which kind of property.
By Warm Home Support ·
Both systems do the same job: they move heat from the surroundings into your home rather than burning a fuel to create it. The difference is where that heat comes from, and that one difference changes the cost, the disruption and the performance of everything that follows.
The short answer
For most UK homes, an air source heat pump is the practical choice. It costs less to install, needs no land, and installs in days rather than weeks.
A ground source heat pump is worth serious consideration where there is suitable land or drilling access, where the property has a high heat demand, or where the system will serve several buildings. It is more efficient and quieter, but the groundworks are a significant part of the project.
How each one works
An air source heat pump takes heat from outdoor air. A fan draws air across a heat exchanger, and a refrigeration cycle raises that low-grade heat to a useful temperature for radiators, underfloor heating and hot water. The type used for wet central heating is called air-to-water.
A ground source heat pump takes heat from the ground, which stays at a far steadier temperature than the air all year. Fluid circulates through buried pipework — either horizontal loops in trenches or vertical boreholes — and the same refrigeration cycle lifts that heat to a usable temperature indoors.
Side by side
| Consideration | Air source (air-to-water) | Ground source |
|---|---|---|
| Heat source | Outdoor air | Ground, via loops or boreholes |
| Land needed | Space for one outdoor unit | Trench area, or borehole access for a rig |
| Installation time | Typically a few days | Longer, with groundworks or drilling first |
| Efficiency through winter | Falls as outdoor air gets colder | Stays steadier — ground temperature varies little |
| Visible equipment | External unit at ground or wall level | Nothing outdoors once work is complete |
| Audible in operation | A fan, audible close up | Effectively silent outside |
| Planning considerations | Siting rules for the outdoor unit | Ground conditions, access, sometimes drilling consent |
| Typical fit | Most homes | Larger properties, rural sites, multi-building schemes |
Efficiency, in plain terms
Heat pump efficiency is described by a coefficient of performance: the units of heat delivered per unit of electricity used. Both technologies deliver several units of heat per unit of electricity, which is why they compare favourably with direct electric heating.
Ground source systems generally achieve a higher seasonal figure because the ground is warmer than the air on the coldest days — and the coldest days are exactly when your home needs the most heat. Air source performance dips in that same weather.
The gap is real but it is often smaller than people expect, and it is easily wiped out by a poor design in either technology. A well-designed air source system with correctly sized radiators will comfortably outperform a badly designed ground source one.
What actually drives the decision
Do you have the land or the access?
Horizontal ground loops need a meaningful area of open ground that can be excavated — usually far more than a typical suburban garden. Boreholes need much less surface area but require a drilling rig to reach the site, which rules out many terraced and mid-town properties on access alone.
If neither is realistic, the comparison ends there.
How much heat does the property need?
The higher the annual heat demand, the more the running-cost advantage of ground source counts against its higher installation cost. A large, older, rural property benefits far more than a compact modern house.
How long will you be there?
Ground source is a long-horizon investment. The ground array itself has a very long service life — much longer than the heat pump connected to it. That is genuinely valuable, but the value accrues over decades.
Disruption
Air source is a heating installation. Ground source is a heating installation plus a groundworks project, with the reinstatement that implies. For some households that is a minor issue; for others it is decisive.
Grants
Under the Boiler Upgrade Scheme, air-to-water and ground source heat pumps currently attract the same standard grant value, and both can qualify for the higher off-gas-grid value where the property meets those conditions. In other words, the grant does not push you towards one technology or the other — the site does.
The current values and the conditions attached to them are on our heat pump grants page. If your property is off the mains gas grid and runs on oil or LPG, the off-gas-grid grant page covers the higher value and its deadline.
Note that air-to-air heat pumps sit outside this comparison entirely: they deliver warm air to rooms rather than heating water, they do not serve radiators or a cylinder, and they attract a different, lower grant value. See air-to-air heat pumps if that is what you had in mind.
Which to choose
Choose air source if you have a normal domestic plot, want the work done quickly, and want the lower installed cost. This is the right answer for the large majority of UK homes.
Choose ground source if you have suitable land or drilling access, a high heat demand, and a long time horizon — and if the quieter, steadier performance is worth the groundworks to you.
Either way, ask for the heat loss calculation and the design flow temperature before you compare prices. Two quotations for the same technology can differ far more than the two technologies differ from each other.
Ready to look at your own property? Start with the eligibility checker, or read more about air source and ground source systems.