What Is a Ground Source Heat Pump?
A ground source heat pump (GSHP) is a highly efficient low-carbon heating system that harvests thermal energy stored in the earth. Unlike air source heat pumps, which rely on outdoor air temperature, a GSHP draws on the ground — which in the UK maintains a relatively stable temperature of around 8–12°C year-round, regardless of the weather above. This thermal stability means GSHPs operate very consistently and are particularly effective in cold winters when air source units see some efficiency reduction.
How Does a Ground Source Heat Pump Work?
A water-glycol solution is circulated through a network of polyethylene pipes buried in the ground. These pipes can be laid horizontally in shallow trenches (typically 1–2 metres deep) across a large area of garden, or inserted vertically into boreholes drilled to depths of 50–200 metres where land area is limited. The fluid absorbs geothermal heat from the soil or bedrock and carries it back to the heat pump unit inside the property. A refrigerant cycle then raises this low-grade heat to temperatures suitable for radiators, underfloor heating, and domestic hot water.
Ground Loops vs Boreholes
The choice between horizontal ground loops and vertical boreholes depends primarily on the land available. Horizontal systems require a large, flat garden — typically around 200–400 square metres per system — and involve significant turf disruption during installation. Vertical boreholes are much more compact but require specialist drilling equipment and are more expensive per unit of heat extracted.
Running Costs and Government Support
GSHPs have some of the lowest running costs of any heating technology. The Boiler Upgrade Scheme offers a £7,500 government grant towards installation. Combined with savings on fuel bills — particularly compared to oil or LPG — payback periods can be competitive for high-energy-use rural properties.