Ground Source Heat Pump Calculator — GSHP Sizing

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.