Air Source vs Ground Source Heat Pumps: Which One Makes Sense for Your Home?

Both air source and ground source heat pumps extract heat from outside and use it to warm your home. But the way they do it, what they cost, and where they work best are quite different.

The basics

Air source heat pumps (ASHPs) pull heat from the outside air. They look like large air conditioning units and sit outside your house against a wall or on a flat surface.

Ground source heat pumps (GSHPs) extract heat from the ground via buried pipes. The ground stays at a relatively constant 8-12C year round, which gives them a theoretical efficiency advantage.

Cost comparison

Ground source is significantly more expensive upfront, mainly because of the groundwork - either boreholes or horizontal trenches. For a full breakdown, see our heat pump costs guide.

Efficiency

Ground source wins on paper. GSHPs typically achieve a Coefficient of Performance (COP) of 4.0-4.5, compared to 3.0-3.8 for ASHPs. In practice the gap narrows, because modern air source units have improved dramatically in cold weather, and the lower installation cost means the overall lifetime cost can favour ASHPs.

Space requirements

ASHP: About 1m x 1m of outside space, at least 1m from a boundary.

GSHP horizontal: Roughly 2-3 times your home's floor area in garden space. Your garden is unusable during installation but recovers within a season.

GSHP borehole: Much less surface area but boreholes go 60-150m deep. More expensive, but the only option if you lack garden space.

Which should you choose?

For most UK homeowners, air source is the practical choice. Lower upfront cost, minimal disruption, and the £7,500 BUS grant makes it genuinely affordable.

Ground source makes sense if you have a large garden and plan to stay 15+ years, you're building a new home, or you want the absolute lowest running costs.

Either way, proper sizing is critical. Make sure your installer does a room-by-room heat loss calculation. For more detail on all types including hybrid systems, see our heat pump types guide. And when you're ready, get free quotes from MCS-certified installers.