Ground Source Heat Pumps in Cornwall: The 2026 Guide

A ground source heat pump exploits the simple fact that the ground stays at a remarkably stable temperature year-round. At 1-2 metres depth in Cornwall, ground temperature varies between roughly 8°C in late winter and 12°C in late summer. At 50+ metres (borehole depth), the temperature is essentially constant at 11-12°C all year.

The system has three loops:

1. Ground loop: a closed circuit of polyethylene pipe filled with a glycol-water mix (typically 25-30% propylene glycol) buried in the ground. A circulation pump moves the fluid through the pipe, picking up heat from the surrounding ground. The fluid returns to the heat pump cabinet at around 0-4°C in winter (after giving up heat to the cold evaporator)
2. Refrigerant loop: inside the heat pump cabinet, a refrigerant absorbs heat from the ground loop fluid via the evaporator, is compressed to a much higher temperature, and gives up that heat in the condenser. Modern GSHPs use R32, R454B, or increasingly R290 refrigerants
3. Heating loop: hot water (typically 35-50°C) leaves the condenser and circulates through your underfloor heating, radiators and hot water cylinder coil, returning at 5-10°C cooler to be reheated

The COP advantage versus ASHP comes from the higher source temperature. An ASHP in January extracts heat from -2°C air; a GSHP extracts from 4°C ground. The smaller temperature lift to deliver 50°C flow means less compression work, which means more heat per kWh of electricity. In a typical Cornwall installation, a well-designed GSHP at A4/W35 conditions hits COP 5.0+, versus ASHP COP 3.5-4.0 at the same flow temperature.

The cabinet itself sits indoors — usually in a utility room, plant room or large airing cupboard — making GSHPs visually invisible compared with the outdoor unit of an ASHP. They also operate near-silently (around 30dB versus 45-55dB for an ASHP fan). For listed buildings, conservation areas and properties where a visible outdoor unit would be problematic, this matters.

Three main ground loop configurations exist, each suited to different sites.

Horizontal trench loops

Straight runs of polyethylene pipe laid in trenches 1.5-2m deep, typically 600-800mm apart, with one or two pipes per trench. Land area required: roughly 2.5-3 times the heated floor area. For a 200m² farmhouse needing a 14kW GSHP, that means 500-600m² of paddock or unused field.

Pros: cheapest loop type (£60-90 per metre of trench installed), quick to dig with a small excavator, easy to repair. Cons: needs lots of land, disruptive to install (the field is unusable for 6 weeks of works and 2-3 years for full reseeding), modest performance compared with boreholes.

Slinky coils

Polyethylene pipe coiled in a "slinky" pattern (overlapping circles) and laid in trenches. Same depth as horizontal but achieves more pipe per metre of trench, reducing land area requirement to around 1.5x heated floor area.

Pros: less land than straight horizontal, similar cost per kW (slightly more pipe but less trench), good for smaller paddocks. Cons: slightly lower performance than equivalent straight horizontal due to thermal interference between coils, more complex to lay correctly.

Vertical boreholes

Boreholes drilled 80-150m deep, lined with polyethylene U-tubes grouted into the borehole with thermally conductive grout. Multiple boreholes drilled 5-7m apart depending on heat extraction load.

Pros: smallest footprint (a 14kW system might need just 3-4 boreholes in a 50m² area), highest performance (constant 11-12°C source temperature year-round, COP 5.0-5.5 typical), no land disturbance after the drilling rig leaves. Cons: most expensive (£15,000-25,000 borehole works for a typical Cornwall domestic install), drilling rig access can be a problem on tight rural sites, granite geology slows drilling.

For most Cornwall GSHP installs we recommend horizontal trenches if land is available, vertical boreholes if not. Slinky is the compromise option for medium land availability. See our GSHP service page.

Cornwall sits on a complex geological foundation: predominantly granite intrusions (the Cornubian batholith, including the Carnmenellis, Land's End, St Austell and Bodmin Moor granites), surrounded by older Devonian killas (mudstones and slates) and overlain by varying superficial deposits.

Granite drilling

The granite is hard but homogeneous, drilling cleanly with diamond-tipped or hammer-bit rotary rigs at typical penetration rates of 8-15m/day. Borehole costs in granite areas (Camborne, Redruth, Helston, St Austell, Bodmin) typically run £45-65 per metre, so a 120m borehole costs £5,400-7,800 each. A 14kW system needing four boreholes is therefore £21,600-31,200 just for drilling.

Killas drilling

The killas (slates and mudstones) are softer and faster-drilling but variable, with occasional voids or fractured zones requiring grouting. Penetration rates 15-25m/day; cost per metre £35-50. Cheaper than granite but with higher risk of having to abandon and re-site a borehole if a void is hit.

Cornwall geothermal opportunity

The Eden Project's 4.5km deep geothermal well drilled in 2019-2021 reached 190°C bottom-hole temperature and now supplies heat and (planned) electricity. While that scale is industrial rather than domestic, it has stimulated interest in shallow geothermal — open-loop systems drawing groundwater from disused mine workings (abundant in central Cornwall) at constant 12-18°C.

For a select number of Cornwall properties near disused mine workings, an open-loop minewater GSHP can deliver SCOP 5.5-6.0+. The complications are water rights, abstraction licensing (requires Environment Agency approval), and pump-failure risk. We have installed two such systems in 2025-2026, both in the Camborne area, and see this as a niche but interesting application.

Where boreholes do not work

The far west of Cornwall (Land's End area) has very shallow soil over granite and high water-table issues, complicating both trenches and boreholes. We have several customers in West Penwith for whom we recommended ASHP rather than fight the geology. See our heat pump page for a free site survey.

GSHP installation cost in Cornwall, May 2026, before the £7,500 BUS grant:

The big cost variable is the ground loop: roughly 35-45% of the total project cost. Within that, borehole drilling versus trenching is the single biggest cost driver — a vertical borehole install can be £8,000-12,000 more expensive than the same property's equivalent horizontal trench install.

Other significant cost lines:

• The GSHP unit itself (typically Kensa Shoebox/Evo, NIBE S1155, Vaillant flexoTHERM, Daikin Altherma 3 GEO): £4,500-9,000 for 8-16kW domestic models
• Hot water cylinder, controls, buffer: £1,500-2,800
• Pipework, manifolds, valves: £700-1,200
• Electrical works: £400-1,200
• Excavation and groundworks contractor (separate from drilling): £3,000-8,000
• Glycol charge and circulation pump: £600-1,200
• Labour for plant room install: £3,500-6,000
• MCS commissioning: £400-600

For a free fixed-price quote on a Cornwall GSHP, call 01209 596 002 or visit our GSHP page.

The headline performance metric is SCOP. Real-world Cornwall figures from CCS installations and the DESNZ Electrification of Heat trial:

The SCOP advantage of 0.5-1.0 over equivalent ASHP translates to roughly 15-25% lower running costs. For a 4-bed Cornwall farmhouse using 22,000kWh of heat annually:

• ASHP at SCOP 3.5: 6,286 kWh electricity, costing £1,551 at standard tariff
• GSHP at SCOP 4.5: 4,889 kWh electricity, costing £1,206 at standard tariff

So £345/year saving versus ASHP, ongoing for the life of the system. Over 20 years that is £6,900 — comfortably less than the £8,000-12,000 capital premium of GSHP over ASHP, but a meaningful contribution.

On a smart tariff (Octopus Cosy, Tracker), the absolute saving is smaller because both systems benefit from cheaper electricity. The relative SCOP advantage is unchanged.

Other performance considerations

• Quietness: GSHPs are essentially silent (the indoor cabinet runs at 30dB, comparable to a fridge). ASHPs are 45-55dB at the outdoor unit. For properties near boundaries or where the outdoor unit would be visible, this is a meaningful quality-of-life factor.
• Longevity: GSHPs typically last 20-25 years versus 15-20 for ASHPs. The ground loop itself has a 50-100 year design life and survives multiple heat pump cabinet replacements.
• Cooling: Many GSHPs offer 'passive cooling' in summer — circulating cool ground loop fluid through the heating system to provide low-grade cooling at zero compressor cost. Useful in Cornwall's increasingly warm summers.
• Defrost cycles: GSHPs have no defrost cycles (no outdoor coil to ice up). ASHPs typically pause for 5-10 mins every 1-2 hours in cold humid Cornwall mornings.

The Boiler Upgrade Scheme pays the same £7,500 grant for ground source heat pumps as for air source. This is one of the more controversial design choices in the scheme — given that GSHPs cost £8,000-12,000 more, the grant covers a smaller proportion of capital. The original 2022 launch had a £6,000 GSHP / £5,000 ASHP differential; this was equalised at £7,500/£7,500 in October 2023.

The eligibility criteria are identical:

• Property in England or Wales (Scotland uses Home Energy Scotland)
• Owner-occupied, privately rented, small non-domestic, or self-build
• Valid EPC (no minimum band, no insulation prerequisite)
• MCS-certified installer
• Not new-build (with self-build exemption), not social housing, not replacing biomass

One nuance: the GSHP grant covers all variants — horizontal closed loop, slinky, vertical borehole, water source (rivers, lakes, ponds), and shared ground arrays serving multiple properties. The shared-array option is interesting for clusters of Cornwall holiday cottages or hamlets where one borehole field can serve 4-8 properties at lower per-unit cost.

Application process is identical to ASHP — see our BUS pillar guide. CCS handles the entire Ofgem process for GSHP customers, including the more detailed survey work needed to evidence ground loop sizing.

Combined with 0% VAT on heat pump installations until March 2027, a GSHP install that quotes at £30,000 list price comes out at £22,500 inc. VAT after grant. Add 0% APR finance via our partner Phoenix Financial Services and the monthly cost over 24 months is roughly £937 — see our finance page.

The GSHP manufacturer landscape is more concentrated than ASHP, and includes a Cornwall-headquartered company.

Kensa Heat Pumps (Truro, Cornwall)

Kensa Heat Pumps is headquartered just up the road from us in Truro and is the UK's largest dedicated GSHP manufacturer. Their Shoebox NX (3-6kW), Evo (4-13kW), and Twin range (12-25kW) units are designed and assembled in Cornwall. Performance is excellent (Shoebox NX achieves SCOP 4.7 at W35 in independent testing) and the after-sales support is responsive — important for the relatively niche GSHP market. Kensa also operates as an installer-and-developer in some markets, particularly shared ground array developments. We frequently install Kensa kit and have a strong working relationship with their technical team. For a Cornwall customer, supporting a local manufacturer is a meaningful additional reason to choose Kensa.

NIBE (Sweden)

NIBE's S1155 and S1255 ranges are the long-time European market leaders, with S1255 integrating a 180L hot water cylinder into the cabinet for compact installations. SCOP performance is class-leading and the Uplink remote monitoring is the best in the business. NIBE is our default specification when the customer prioritises reliability and monitoring depth over UK-manufacturer support.

Vaillant (Germany)

Vaillant flexoTHERM exclusive is well-engineered, attractive cabinet design, and benefits from Vaillant's strong UK engineer network. Slightly less efficient than NIBE or Kensa at the top end. Often specified for customers who already have a Vaillant boiler and want familiar controls.

Daikin (Japan)

Daikin Altherma 3 GEO is a competent unit but not Daikin's strongest product line — they focus more on ASHP. Specified rarely.

Viessmann (Germany)

Vitocal 222-G and 333-G are excellent, integrating cylinder and controls cleanly. Premium pricing. Our recommendation when budget allows and the Vitoconnect monitoring platform is preferred.

Bosch (Germany)

Bosch Compress 7000i LWM is the volume option, well-engineered but not class-leading on SCOP. Good for budget-conscious GSHP installs.

For most Cornwall GSHP installs in 2026, our default specification is Kensa Evo (for the Cornish manufacturing connection) or NIBE S1155 (for the controls and monitoring depth). See our GSHP page.

For a Cornwall farmstead — a 4-5 bed period property, off mains gas, on oil or LPG, with paddock land available — both ASHP and GSHP are viable. Here is the honest comparison.

Worked example: 4-bed Helston farmhouse, 28,000 kWh/year heat demand

So the GSHP saves around £400/year on Cosy versus ASHP, paying back the £9,000 capital uplift in about 22 years. That is longer than ASHP design life but well within GSHP design life (20-25 years).

The pure-cash case is therefore tight. The reasons to choose GSHP over ASHP for a Cornwall farmstead are usually:

1. You have land and want to use it — paddock, smallholding, equestrian field; zero opportunity cost
2. You want zero outdoor visual impact — listed building, AONB, conservation area, principal-elevation issue
3. You want quietness — close-boundary properties or noise-sensitive sites
4. You value longevity — 20-25 year heat pump life vs 15-20 for ASHP
5. You like the idea of "free" passive cooling — useful as Cornwall summers warm
6. You support a Cornwall manufacturer (Kensa) — meaningful local economy point

For most rural Cornwall farmsteads we present both options and let the customer choose. Roughly 30% choose GSHP, 70% ASHP. For urban/suburban Cornwall properties, ASHP is overwhelmingly the right choice given the lack of land and cheaper retrofit. Call 01209 596 002 for a free survey or visit our GSHP page.