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Ground Source Heat Pump Calculator — GSHP Sizing
Size a ground source heat pump system for your property. Calculate ground loop length, borehole depth, COP, running costs, and savings versus a gas boiler.
From heat loss calculation or EPC
Accessible area for ground works
Default = Ofgem cap Jul-Sep 2026 (7.33p/kWh)
Default = Ofgem cap Jul-Sep 2026 (26.11p/kWh)
Typical old boiler 70-80%, condensing 90%+
35°C UFH, 45°C oversized rads, 55°C standard rads
Typical UK 1800-2200 hours
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How We Calculate This
This calculator sizes a ground source heat pump system based on your property heat loss and the thermal properties of your ground conditions. It estimates loop length or borehole depth needed to extract sufficient heat from the ground.
System sizing
- Heat pump capacity: Based on property heat loss plus hot water demand, rounded up to the nearest 2 kW unit size
- Ground extraction: The heat pump extracts heat from the ground equal to output minus electrical input (output × (1 − 1/COP))
- Loop length: Total extraction needed divided by the ground-specific extraction rate
- COP estimation: An indicative figure based on loop type and required flow temperature — confirm the MCS SCOP against the heat-pump datasheet
Cost comparison
Running costs are compared against a gas boiler at the specified efficiency. Annual heat demand is (property heat loss + hot water demand) × running hours; dividing this by the COP gives the annual electricity consumption. CO₂ savings use the DESNZ/DEFRA 2026 GHG conversion factors (natural gas 0.18231, grid electricity 0.131 kgCO₂e/kWh). The grid factor falls sharply each year as the grid decarbonises. Default energy prices are the Ofgem cap for 1 July–30 September 2026; override them in Advanced options with your own tariff. For the up-front picture — installation cost bands for ASHP and GSHP, the £7,500 BUS grant and payback period — see our UK heat pump cost calculator.
Frequently Asked Questions
For horizontal ground loops, you typically need 2-3 times the floor area of your home. A 10 kW system might need 400-600 m² of garden for horizontal trenches at 1.2m depth. Vertical boreholes need much less surface area (around 25 m² per borehole) but cost more to drill. Boreholes are often the only option for smaller gardens.
Ground source heat pumps typically achieve a seasonal COP of 3.5-4.5, meaning they produce 3.5-4.5 kWh of heat for every 1 kWh of electricity consumed. COP depends on ground type, loop design, and the flow temperature required. Lower flow temperatures (35°C for underfloor heating) give higher COP than higher temperatures (55°C for radiators).
Typical installed costs range from £15,000-£25,000 for a domestic GSHP system including ground works. Horizontal ground loops are cheaper (£2,000-5,000 for trenching) while vertical boreholes cost £6,000-12,000 or more. The UK Boiler Upgrade Scheme (BUS) offers a £7,500 grant towards GSHP installation costs.
GSHPs are more efficient (COP 3.5-4.5 vs 2.5-3.5 for ASHP) because ground temperatures are more stable than air temperatures. They are quieter with no external fan unit. However, they cost more to install due to ground works. GSHPs are better suited for new builds or properties with adequate garden space.
Rock/granite and wet clay provide the best thermal conductivity and heat extraction rates. Borehole figures follow VDI 4640 Part 2: this tool uses conservative rates of about 52 W per metre of probe for wet clay, 65 W/m for hard rock and 35 W/m for dry clay. Horizontal trench figures (about 25 W per metre of pipe for wet clay, 30 for rock, 10 for dry clay) are a trench-pipe design convention, not VDI’s W/m² ground-area values. UK installers size the ground array from the MCS 022 look-up tables; a ground thermal conductivity (TRT) test confirms the rate for boreholes on your site.
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Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.