Ground Source vs Air Source Heat Pump: Which Is Right for a UK Home?

How each works

Both ground source and air source heat pumps move heat from outside to inside, using electricity to drive the process. Neither generates heat; they move it. The same principle applies to a refrigerator running in reverse.

An air source heat pump (ASHP) extracts heat from the outdoor air using a fan-driven heat exchanger, typically mounted at the side or back of the house. Modern units work efficiently down to outdoor temperatures of about minus 15°C, although efficiency drops in very cold weather.

A ground source heat pump (GSHP) extracts heat from the ground using a network of pipes buried in trenches or in vertical boreholes. Ground temperature is more stable than air temperature (around 8 to 12°C all year in the UK at depth), so GSHPs run at a higher and more consistent efficiency than ASHPs throughout the year.

Cost comparison

The ground loop itself lasts much longer than the heat pump unit, so GSHP replacements only require swapping the indoor unit, not redrilling boreholes.

Where each works best

Air source

• Most UK homes
• Properties with an outdoor wall facing away from neighbours (for noise)
• Limited garden space
• Lower upfront budget
• Properties already insulated to a reasonable standard

Ground source

• Larger detached homes
• Rural properties with substantial gardens for trench loops
• Properties where running cost matters more than upfront cost (long ownership horizon)
• Off-grid or oil-heated properties
• Properties already heated by underfloor heating (which works particularly well with the lower flow temperatures of GSHPs)

What about hybrids?

Hybrid heat pump systems pair a small heat pump with a backup gas boiler that runs on the coldest days of the year. Hybrid systems are not eligible for the BUS grant in most cases because the grant requires the gas boiler to be removed entirely. Hybrid systems can be cost-effective in poorly insulated homes that would otherwise need extensive retrofit before a full heat pump would work, but they keep the gas connection running, which counters the carbon objective.

How heat pumps affect EPC

Heat pumps run on electricity. Under the current SAP methodology used to calculate EPC ratings, electric heating is sometimes penalised because of legacy assumptions about grid carbon intensity. This means switching from a gas boiler to a heat pump can sometimes reduce your EPC rating slightly even though the property is genuinely lower carbon.

The government is consulting on revising SAP. Until that happens, get an EPC simulation from your installer if EPC rating matters for your situation (for example, if you let the property and need to maintain compliance with MEES).

You can check your current EPC rating by searching your address on Property Passport UK at [/search](/search). The platform pulls EPC data directly from the official EPC Register for every property in England and Wales.

What insulation work needs to come first

Both heat pumps work best in well-insulated homes. Before installing either, you should have:

• Loft insulation to current standards
• Cavity wall insulation if you have a cavity wall
• Heating controls (TRVs, weather compensation)
• Ideally, larger radiators or underfloor heating to allow lower flow temperatures

The BUS grant requires loft and cavity wall insulation to be in place (or formally exempted) before the grant can be paid. See the Boiler Upgrade Scheme guide for the full eligibility criteria.

Check your EPC on Property Passport UK

Property Passport UK shows the official EPC rating for every property in England and Wales, sourced directly from the EPC Register. You can look up any address at [propertypassport.uk/epc](/epc), or search by postcode at [/search](/search) to see the rating, expiry date, recommended improvements, and the gap between current and potential efficiency.

Related guides

• EPC C rating by 2030 explained
• MEES regulations landlord guide
• Cost of going from D to C on an EPC
• Boiler Upgrade Scheme explained