Most UK homeowners looking into heat pumps only ever seriously consider one type: air source. It’s cheaper to install, doesn’t touch the garden, and is what nearly every installer quotes first. Ground source heat pumps get far less attention, but for the right property they can run more efficiently, more consistently through winter, and last longer - at a meaningfully higher upfront cost. This guide compares both technologies on the things that actually decide which one suits a given home: cost, space, efficiency, noise, planning rules and lifespan, using current UK figures rather than a generic “heat pumps are great” pitch.
How each type actually works
Both technologies do the same basic job - moving heat from somewhere cooler into your home, using electricity to run a compressor rather than burning fuel - but they draw that heat from different sources. An air source heat pump extracts heat from the outside air via an outdoor unit, similar in size and appearance to a large air conditioning condenser. A ground source heat pump extracts heat from the ground instead, via a loop of pipe buried in trenches or sunk into a borehole, circulating a fluid that picks up the earth’s stored heat before it reaches the heat pump unit itself, usually installed indoors.
The difference in heat source is what drives almost every other difference between the two systems: installation cost, space needed, how consistently they perform through a UK winter, and how disruptive the install itself is.
Installed costs compared
According to Energy Saving Trust, a typical air source heat pump installation in the UK costs around £12,000. A ground source system costs substantially more: EST puts a trench-based installation at around £29,000, with government scheme data showing installed costs for ground source systems ranging from roughly £18,700 to £38,200, averaging around £25,300 before any grant is deducted. Where a borehole is needed rather than a trench - usually because the garden isn’t large enough for horizontal trenches - the cost climbs further still, since it requires specialist drilling rig access and a geological survey beforehand.
Both technologies are eligible for the same Boiler Upgrade Scheme grant support in England and Wales, so the grant itself doesn’t change the comparison between them - it simply reduces the up-front cost of whichever one you choose by the same amount. The roughly £13,000-£17,000 cost gap between air and ground source is the single biggest reason most UK homeowners default to air source without looking further, and it’s a completely reasonable reason to do so unless the other factors below tip things the other way for your specific property.
Space, garden and disruption
This is usually the deciding factor before cost even comes into it, because a lot of UK homes simply don’t have the option of ground source regardless of budget. A horizontal ground loop needs a garden large enough to dig trenches - typically two trenches of 30-40 metres in length for an average three-bedroom home, more for a larger or less well-insulated property - with the ground itself suitable for digging and accessible to machinery from a road entrance, and no trees nearby (roots interfere with the trench and the pipework). A borehole needs much less surface space - the shaft itself is only around 20cm wide - but drilling rig access is still required, along with a specialist geological survey to confirm the ground is suitable, and boreholes typically run anywhere from 75 to 200 metres deep depending on the heat needed.
An air source heat pump needs none of this. It requires an outdoor unit fixed to a wall or standing on the ground with reasonable airflow around it - broadly comparable in footprint to a large air conditioning unit - and involves nowhere near the disruption of digging up a garden or bringing in a drilling rig. For a terraced house, a home with a small garden, or anyone who doesn’t want their garden dug up for a week or more, air source is usually the only realistic option regardless of what the cost or efficiency comparison says.
Indoors, the difference runs the other way round: a ground source system’s indoor unit is considerably larger than an air source one - Energy Saving Trust describes it as roughly the size of an American-style fridge (about 120cm x 60cm x 60cm) - and it often houses the hot water cylinder too, so it needs a proper utility space or plant room rather than a small cupboard.
Efficiency and cold-weather performance
Both technologies are measured the same way - Coefficient of Performance (CoP), the ratio of heat output to electricity input - and both typically deliver three to four units of heat for every one unit of electricity used. Where they differ is consistency. Air temperature in the UK fluctuates between roughly -5°C and 25°C for most of the year, and a heat pump has to work hardest, and least efficiently, exactly when it’s coldest outside - which is also when a home needs the most heat. Ground temperature, by contrast, stays above roughly 5°C year-round a few metres down, regardless of what’s happening at the surface. That stability is the core efficiency argument for ground source: it keeps delivering a consistent CoP through a cold snap in January in a way an air source system’s efficiency will dip during.
In practice, this means a ground source system tends to need a smaller electricity input to deliver the same heat on the coldest days of the year, which is where its running-cost advantage over air source is greatest. It’s worth being realistic about the size of that advantage, though - it isn’t a dramatic difference for most well-installed modern systems, and a correctly sized air source heat pump in a reasonably insulated home still performs well through a typical UK winter. The gap matters most for larger, harder-to-heat properties, or anyone specifically prioritising the lowest possible running cost over the lowest upfront cost.
Noise and planning permission
Air source heat pumps have an outdoor unit that runs more or less continuously in cold weather, which is why noise and planning rules focus almost entirely on this technology - a ground source system’s heat pump unit sits indoors, so it isn’t subject to the same outdoor-noise planning tests.
Most air source heat pump installations in England are “permitted development,” meaning no planning application is needed, provided the outdoor unit doesn’t exceed 1.5 cubic metres in volume (0.6 cubic metres for a flat) and, for most houses, no more than one or two units are installed. Listed buildings and Scheduled Monuments always need planning permission regardless of these limits. The rules changed materially on 29 May 2025: England scrapped the old blanket requirement that a unit be sited at least one metre from the property boundary, replacing it with a noise-based test under the updated MCS 020a standard - in short, a unit can now be positioned closer to a boundary than the old rule allowed, provided it’s demonstrated to meet the noise standard at that distance. Scotland, Wales and Northern Ireland still use the earlier MCS 020 standard at the time of writing, so the specific rule that applies depends on where the property is.
The practical upshot: check with your installer whether your proposed unit position and model pass the current MCS 020a noise calculation for your property, particularly on a terraced or semi-detached home with close neighbours, rather than assuming an old “just keep it a metre from the fence” rule of thumb still applies.
Lifespan and maintenance
The heat pump unit itself - whether air or ground source - typically lasts in the region of 15-20 years before it needs replacing, similar to a modern gas boiler, and benefits from an annual service to keep it running efficiently. Where ground source has a genuine long-term advantage is the ground loop: a properly installed horizontal loop or borehole is expected to last 50 years or more, since it’s just buried pipework with no moving parts, exposed to almost none of the wear a boiler or heat pump unit experiences. In practice, this means a ground source system’s biggest cost - the groundworks - is a largely one-off expense, and a future replacement heat pump unit doesn’t require redoing the trenches or borehole, only reconnecting to the existing loop.
So which should you choose?
For most UK homes, air source is the practical default: lower upfront cost, no garden disruption, and now more straightforward planning rules under MCS 020a. It’s the right choice for terraced and semi-detached homes, smaller gardens, and anyone who wants a heat pump without a major groundworks project.
Ground source is worth serious consideration where a property has the land for it - a reasonably large garden or rural plot with machinery access, or a new-build where groundworks are happening anyway - and where the buyer specifically values the most consistent possible winter performance and the longest-lived core installation, and can absorb the higher upfront cost even after the same grant support is applied. It’s a genuinely different proposition rather than simply “the more expensive option,” and for a large, hard-to-heat rural property it can be the more sensible choice despite costing more to install.
Either way, the right starting point is the same: get a proper heat loss survey for your specific property rather than working from averages, since the size and cost of either system depends on your actual heat loss, not a rule of thumb. Our Heat Pumps service page can match you with a local MCS-certified installer who’ll survey your home and quote for both options where relevant, and if you’re still weighing up heat pumps against solar or insulation first, our guide on sequencing a self-funded retrofit covers that decision in more detail.
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