Air Source vs Ground Source Heat Pump: Which Suits Your Home

Both technologies use the same vapour-compression cycle to move heat from a low-temperature source to the higher-temperature heating water, and both are limited by the temperature lift involved. The key difference is the source temperature: outdoor air swings from mild to well below freezing, while the ground a couple of metres down stays close to the annual mean, around 8–12°C in the UK. Because efficiency falls as the lift rises, the GSHP's warmer, steadier source gives it an efficiency advantage that is greatest exactly when it matters most — the coldest days.

That physics, however, sits behind the same fabric-and-emitter logic that governs any heat pump. Whether the source is air or ground, the system runs efficiently only if the flow temperature is low, which in turn depends on a modest heat loss and adequately sized emitters. A poorly insulated house with small radiators will run a GSHP at high flow temperatures and lose much of its theoretical advantage; a well-detailed, low-loss house lets even an ASHP run cool and efficiently.

The decisive practical factor is usually cost and site. A GSHP's ground loops or boreholes add substantial capital and need either land for horizontal trenches or drilling access for boreholes, plus the ground array must be sized so it does not cool over the heating season. An ASHP needs only an external unit position, with noise and defrost to manage. For most homes the ASHP's far lower cost outweighs the GSHP's efficiency edge; the GSHP comes into its own with high, sustained demand, available land and a long ownership horizon.