An air source heat pump (ASHP) installs in the UK for roughly £8,000 to £14,000 before grant, while a ground source heat pump (GSHP) lands at £18,000 to £40,000 because the groundwork dominates: a horizontal collector loop wants 600 to 1,000 square metres of ground, a vertical borehole costs around £6,000 to £10,000 per 100 metres drilled, and that geology spend has nothing to do with the heat pump unit itself. The £7,500 Boiler Upgrade Scheme grant applies equally to both. The catch is that the post-grant gap stays wide while the running-cost gap is narrow.
Last reviewed: May 2026
TL;DR
- ASHP install: £8,000 to £14,000 typical, BUS grant takes the net to £500 to £6,500 for most UK homes.
- GSHP install: £18,000 to £40,000 typical, BUS grant takes the net to £10,500 to £32,500: still a step up.
- SCOP (seasonal coefficient of performance): ASHP 3.0 to 3.8, GSHP 4.0 to 4.5 per Energy Saving Trust field data.
- Operating cost: a SCOP of 4.5 versus 3.3 is around a 27% reduction in kWh consumed for the same kWh of heat delivered.
- Capital payback on the GSHP versus ASHP delta is typically 15 to 25 years at 2025-2026 tariff levels: most owners do not recoup the groundwork on running costs alone.
What you are actually paying for
An ASHP is a refrigerant cycle in a metal box that sits outside the house, lifts low-grade heat out of the ambient air, and delivers it to a flow-and-return water loop into the heating system. The capital cost is the unit, the indoor cylinder if a new one is needed, refrigerant pipework, electrical commissioning, and labour. There is no groundwork.
A GSHP is the same refrigerant cycle, but it pulls low-grade heat from a buried collector loop or borehole array. That ground loop is the heat source: it carries a glycol-water mix at around 0 to 8°C through the heat pump's evaporator. The collector array is where the money goes.
Three groundwork configurations exist in UK practice:
- Horizontal slinky. Trenches roughly 1 to 1.5 metres deep, spread over 600 to 1,000 m² of unobstructed ground. Cheapest groundwork option but needs land.
- Vertical borehole. One or more 80 to 200 metre boreholes drilled into the substrate. Suits compact urban plots. Drilling is the cost driver: roughly £6,000 to £10,000 per 100 m drilled depending on geology.
- Open loop / water source. Pumped abstraction from an aquifer, lake or borehole pair. Requires Environment Agency abstraction permission. Rare outside specific rural settings.
Install cost ranges in 2026
The Microgeneration Certification Scheme (MCS) and Energy Saving Trust cost ranges, combined with installer quote samples gathered through 2025 and early 2026, point to the following typical bands.
| Configuration | Install range (pre-grant) | After £7,500 BUS | Notes |
|---|---|---|---|
| ASHP, retrofit, 3-bed semi | £8,000 to £12,000 | £500 to £4,500 | Standard radiator upgrade often required |
| ASHP, larger detached, deeper retrofit | £12,000 to £16,000 | £4,500 to £8,500 | Hot water cylinder upgrade and pipework changes |
| GSHP horizontal slinky | £18,000 to £28,000 | £10,500 to £20,500 | Requires 600 m² plus accessible land |
| GSHP vertical borehole | £25,000 to £40,000 | £17,500 to £32,500 | Geology determines drilling depth and cost |
| Water source / open loop | £20,000 to £45,000 | £12,500 to £37,500 | Environment Agency licence often needed |
The 25 to 40 grand band for vertical GSHP is the area that scares off most homeowners. It does not mean GSHP is wrong; it means the case has to be made on something other than headline grant economics.
SCOP and what it actually means for the bill
Seasonal Coefficient of Performance (SCOP) is the ratio of heat delivered to electricity consumed across a full UK heating season. A SCOP of 3.5 means the heat pump delivers 3.5 kWh of heat for every 1 kWh of electricity drawn. Higher is better.
Energy Saving Trust field trial data published over 2023 and 2024 consistently shows GSHP SCOP in the 4.0 to 4.5 band, while ASHP SCOP runs 3.0 to 3.8 depending on installation quality and how cold the local design temperature gets. The physics behind the gap is straightforward: ground temperature at 1.5 metres depth in the UK stays around 8 to 12°C all winter, so the heat pump is lifting from a warmer baseline. Air can be down at minus 3°C in a Manchester January cold snap, and the cycle has to work harder. To put a number on the running-cost gap: a typical 9,000 kWh heat demand at a SCOP of 3.3 (ASHP) means 2,727 kWh of electricity. The same demand at SCOP 4.5 (GSHP) means 2,000 kWh. At a heat pump tariff blended rate of 18p per kWh, that is £490 versus £360, a saving of roughly £130 per year. Across a 20-year asset life, that is around £2,600 of cumulative running-cost saving. The groundwork gap is £10,000 to £25,000.
The post-grant economics: why most owners go ASHP
Run the numbers and the picture is unambiguous. The BUS grant of £7,500 applies to both technologies, so the absolute grant amount is identical. But the relative impact is asymmetric: £7,500 closes most of the gap on a £10,000 ASHP, and only a fraction of the gap on a £30,000 GSHP.
The CCC's 2025 progress report to Parliament notes that ASHP installs were running at around seven times the volume of GSHP installs through 2024 and 2025, almost entirely because of upfront cost. On the ground, this is what installers see in their order books across the South East, the Midlands and the North West. GSHP volume concentrates in custom new-builds, large rural retrofits where land is not the limiting factor, and a small number of community-scale shared loop projects.
When GSHP actually wins
Three scenarios genuinely favour GSHP on the numbers.
High heat demand off-gas rural homes. A six-bedroom Grade II listed farmhouse in a Welsh postcode with no mains gas, currently on heating oil at around 13p per kWh effective, has a heat demand that could exceed 25,000 kWh. The SCOP gap matters more at scale: at 25,000 kWh demand, the 1.2 SCOP difference equates to roughly £400 per year, and the listed-building constraints make an outdoor ASHP unit harder to site under planning.
Shared ground arrays. Community schemes (Aberdeen Heat and Power and several Cornwall affordable housing trusts have run pilots since 2022) spread the borehole capital cost across many dwellings, so the per-home capital number drops dramatically.
New-build with groundwork already on programme. If excavators are on site for foundations and drainage, the marginal cost of slinky trenches is far below the retrofit cost. Custom new-builds in the Cotswolds, Suffolk and North Yorkshire have used this efficiency through 2025 and into 2026.
The installation quality variable
The single biggest factor in real-world heat pump performance is not technology choice, it is installer quality. An MCS-certified installer must complete an MIS 3005-D heat loss calculation, size the unit correctly, and design radiators or underfloor for a low flow temperature (ideally 35 to 45°C). A poorly designed system running at 55°C flow temperature will turn an advertised SCOP of 4.0 into a delivered SCOP of 2.7, and that gap obliterates any technology choice advantage on the spreadsheet.
Here is where it breaks. Two homeowners with otherwise identical specifications: a Crawley three-bed semi installed by an experienced MCS firm with a full radiator upsizing programme delivered 12-month average COP of 3.6 in trial data. The same product, same size, installed in a Reading three-bed semi without radiator upgrades, delivered 2.4. Same hardware, very different outcome.
Regional and devolved-nation differences
In Scotland, Home Energy Scotland grants and interest-free loans (administered by the Energy Saving Trust on behalf of the Scottish Government) can stack to give a household up to £15,000 of combined capital support for an ASHP install: the £7,500 grant plus an optional £7,500 loan. Scotland also has a £1,500 rural uplift in postcodes including IV, KW, HS, ZE and parts of PA. For a GSHP install in the Highlands, the combined support can move the affordability needle materially.
In Wales, the Nest scheme can stack with BUS for households meeting low-income thresholds. England has the BUS grant only, with no loan layer.
Northern Ireland does not currently have a direct equivalent to BUS at the same value level. Households in Belfast, Derry and across the province route through Department for the Economy energy efficiency support, which is structured differently.
Maintenance and lifespan
ASHP lifespans are typically quoted at 15 to 20 years, GSHP at 20 to 25 years for the heat pump unit and 50+ years for the ground loop itself. Annual service costs for both are similar at £150 to £250 per year. The GSHP edge on lifespan is real but the discounted cashflow impact is small at typical UK discount rates: £200 of saving in year 22 is worth very little in today's terms.
The straight answer
For most UK retrofit homeowners, ASHP is the install that the post-grant economics support. GSHP is the install for homes with high heat demand, sufficient land, or new-build sites where the marginal groundwork cost is much lower than the retrofit equivalent. Running-cost savings on GSHP are real but rarely repay the capital gap inside an asset life.
Frequently asked questions
Is GSHP always more efficient than ASHP?
Yes on paper. Field data from the Energy Saving Trust consistently puts GSHP SCOP at 4.0 to 4.5 against 3.0 to 3.8 for ASHP, because ground temperature is more stable than winter air temperature.
Can the BUS grant pay for the borehole drilling?
The £7,500 BUS grant goes against the total eligible installation cost, including drilling and collector loop where they form part of the GSHP project. It does not pay for landscaping or remediation outside the heat pump install scope.
How much land does a horizontal GSHP loop need?
Around 600 to 1,000 square metres for a typical 9 to 12 kW system, depending on soil type and slinky pitch. A trial trench is normal before final design.
Does a GSHP work without underfloor heating?
Yes. Oversized radiators designed for low flow temperatures (35 to 45°C) work with both ASHP and GSHP. Underfloor improves efficiency further but is not a precondition.
How long do heat pumps last?
ASHPs are typically rated 15 to 20 years for the unit, GSHPs 20 to 25 years, with the ground loop itself often quoted at 50+ years.
Is the noise difference significant?
ASHP outdoor units generate fan noise (typically 40 to 55 dB at one metre, depending on model and mode). GSHPs are indoor-mounted and quiet, with no external fan. Permitted Development noise limits for ASHP under MCS 020 apply where planning is via PD.