Air Source Heat Pump vs Ground Source Heat Pump

Air Source vs Ground Source Heat Pump: Which Should You Get?

If you're choosing between an air source heat pump (ASHP) and a ground source heat pump (GSHP), here's the honest answer for almost everyone: get the air source. Ground source is better technology. It's quieter, it lasts longer and it runs cheaper. It just isn't better by enough to justify what it costs, and the gap doesn't close no matter how long you own it.

Here's the working.

The Numbers Side by Side

Costs and land requirements are from the Energy Saving Trust, which puts a trench-based ground source install at around £15,000 and says a newbuild three-bedroom house needs "two trenches of 30-40 metres in length", with a bigger loop for larger or less well insulated homes. The air source figure is the same source: "The typical cost of installing an air source heat pump is around £12,000", which is why we use £9,000 to £13,000 across this site for a job that varies by house size.

Note what the Energy Saving Trust doesn't give you: a minimum plot size. You'll see numbers like "you need 600 square metres" thrown around online, including on this page until we checked. Nobody official publishes one, because the answer depends on your heat demand and your soil, and the only person who can tell you is an installer standing in your garden.

Why Air Source Wins for Most People

Nine out of ten UK heat pump installations are air source, and it isn't fashion. It's the price difference, and the fact that the efficiency advantage can't catch it.

Work it through. Take a house needing 12,500 kWh of heat a year at the current 26.32p electricity cap. An air source system at SCOP 3.5 uses 3,571 kWh and costs £940 a year to run. Ground source at SCOP 4.2, the figure we use site-wide, uses 2,976 kWh and costs £783. That's £157 a year better.

Now the cost. Both get the same £7,500 grant, so the grant cancels out and what matters is the gap between the installed prices. On the Energy Saving Trust's figures that's roughly £4,000: £15,000 for a trench system against about £11,000 for a mid-range air source install. £4,000 divided by £157 is 25 years, on a machine with a 20 to 25 year life. Go to a borehole, which the Energy Saving Trust says costs "considerably more" again without putting a figure on it, and you're past the life of the equipment before you break even.

Then there's the installation. An air source unit goes in over two or three days: a box outside, pipework in, done. Ground source means machinery in your garden, trenches across it, and a site the Energy Saving Trust says needs to be free of trees (roots wreck the digging) and reachable by plant from a road entrance. If space is tight you're drilling instead, which usually needs a thermogeological survey first.

Where the Efficiency Gap Actually Comes From

Ground source is more efficient for two good reasons. The ground sits at a stable 10–12°C all year, so the pump is always lifting heat from a warm-ish source rather than from air that might be at freezing. And because it isn't pulling heat out of damp winter air, it never has to stop and defrost a coil, which is a real efficiency cost for air source in a cold, wet January.

We've quoted these as SCOP, seasonal coefficient of performance, rather than the single-point COP numbers on manufacturer brochures. SCOP is what you actually pay for: it's the average across a whole heating season, defrost cycles and all. A brochure COP of 5.0 measured at 7°C outside and a 35°C flow temperature is a real measurement, it just isn't a bill. Real monitored UK air source systems average 3.87 across the 252 machines reporting to heatpumpmonitor.org, which is why 3.5 is the conservative number we use throughout this site.

Worth noting in passing: at 26.32p for electricity and 7.97p for gas, a 90% gas boiler delivers heat at 8.86p per kWh and an air source heat pump at SCOP 3.5 delivers it at 7.52p. The break-even point is a SCOP of 2.97. Both of these machines beat gas now, which they didn't under the July 2026 cap. Ground source just beats it by more.

The honest caveat: there's no equivalent large public dataset of monitored domestic ground source systems in the UK, so treat the 4.2 above as a reasonable expectation rather than a measured fact. Push it to a flattering 4.5 and the annual gap goes to £209, which still takes 19 years to repay £4,000. The conclusion doesn't move.

When Ground Source Actually Makes Sense

There are genuine cases. Consider it if:

• You're building. If the diggers are already on site and the garden is a building plot rather than a lawn, the trenching cost collapses. This is the single best reason.
• You have a big, heat-hungry property. The efficiency advantage scales with how much heat you use. At 40,000 kWh a year rather than 12,500, that £157 becomes about £500 and the £4,000 gap pays back in eight years, which is a completely different conversation.
• Siting an outdoor unit is genuinely impossible. A listed building, a tight conservation-area frontage, or a boundary where no air source unit can meet the noise limits.
• You want it to last. The ground loop is effectively permanent. In 25 years you replace the heat pump in the utility room and reuse the expensive bit in the garden. That's a real long-term argument, it just doesn't pay back inside one owner's stay in most houses.

The Cold Weather Question

People worry that air source stops working in a cold snap. Modern units don't. Published operating ranges typically run down to -20°C or -25°C, which is well past anything a UK winter delivers outside the Highlands. Efficiency does drop when it's genuinely freezing, and defrost cycles eat into it, but the system keeps making heat.

Ground source doesn't have the problem at all, because 10°C of soil in January is still 10°C of soil. That's a real advantage on the coldest fortnight of the year. It's worth money. It isn't worth £4,000 for most houses.

What About Noise?

An air source unit makes a noise. Not much of one, and quieter every product generation, but it's a fan and a compressor and it runs hardest when it's coldest. The thing to check is placement.

Permitted development in England is conditional on the installation meeting the MCS Planning Standards sound calculation (MCS 020 a), assessed at your nearest neighbour's habitable-room window. Don't accept a reassurance: ask for the completed calculation and the sound power level (LwA) of the exact unit being quoted. A good installer sites the unit to be comfortably inside the limit rather than scraping past it.

A ground source system puts nothing outside at all. If your only possible unit position is under a bedroom window or a metre from a boundary fence, that matters more than any spreadsheet.

The Bottom Line

For most UK homes, air source is the clear winner. It's thousands cheaper, it goes in without turning your garden into a building site, and the efficiency advantage of ground source takes about 25 years to repay the difference, which is the whole life of the machine.

Go ground source if you're building from scratch, if the property is large enough that the running cost gap gets serious, or if there's genuinely nowhere to put an outdoor unit. Those are good reasons. "It's more efficient" on its own isn't, because you can buy an awful lot of electricity for £4,000.

For help choosing a specific model, see our best heat pumps UK guide and our heat pump costs guide.