The Short Answer
We'd choose air source for almost everyone. Ground source is quieter outside and runs cheaper, but real installs cost about £13,200 more to fit (DESNZ medians across all sizes), and it saves about £89 a year on a typical 3-bed, so the gap never closes.
We'd go ground source if you're building or have nowhere to put an outdoor unit. Even in a very large house, at real install costs the gap would take about 35 years to close, past a heat pump's life.
The Numbers Side by Side
| Air source | Ground source | |
|---|---|---|
| Real installs (DESNZ) | Middle half £11,128 to £15,627, April to June 2026; 2025/26 median £13,021 | 2025/26 median £26,200 |
| Energy Saving Trust | Typical around £12,000 | Around £15,000 with trenches; a borehole considerably more |
| Boiler Upgrade Scheme grant | £7,500 | £7,500 |
| SCOP we use | 3.5 | 4.0 |
| Running cost, 9,500 kWh of heat | About £714 a year | About £625 a year |
| Space | An outdoor unit | 2 trenches of 30 to 40 metres for a new-build 3-bed, or a borehole 75 to 200 metres deep |
Running costs at the 26.32p price cap rate, for our typical 3-bed's heat (from DESNZ's measured gas use). The 307 systems on heatpumpmonitor.org with a year of data, of all types together, averaged 4.01 when we checked, though those are homes whose owners choose to publish their data. Both of our SCOPs are our assumptions, not measurements. We use 15 years as a heat pump's life in paybacks.
Why Air Source Wins for Most Homes
Both get the same grant, so the difference is the installed price. On the Energy Saving Trust's headline figures the gap is about £3,000, which at £89 a year takes about 34 years. On DESNZ's figures for real installs in 2025/26 (medians across all sizes) it's about £13,200, which you'd never get back. Ground source also means digging trenches across the garden, or drilling a borehole.
The efficiency gap is real: Kensa says the ground stays between about 8C and 12C even in a UK winter, so a ground source heat pump always lifts heat from a mild source and never needs to defrost a coil.
When Ground Source Makes Sense
- You're building, and the diggers are already on site.
- A big, heat-hungry house, but only with a keen quote. At 40,000 kWh of heat a year the gap grows to about £376 a year. If your ground source quote is only about the Energy Saving Trust's typical-home gap of £3,000 more than air source, that pays back in about 8 years. At DESNZ's real-install gap it's about 35 years, past a heat pump's life, so in our view a big house alone isn't enough: compare the two quotes first.
- Nowhere for an outdoor unit, for space, planning or noise reasons.
Our ground source guide covers it in full.
Cold Weather and Noise
Air source keeps making heat in a UK cold snap, though efficiency drops and it has to defrost. Ground source doesn't notice. An air source unit makes some noise; in England and Wales permitted development depends on meeting the MCS 020 a) noise standard at the nearest neighbour's window, so ask the installer for the completed calculation. Ground source puts nothing outside.
Our Verdict
Air source for most homes; ground source if you're building or an outdoor unit won't work; a large house on its own, in our view, rarely closes the gap at real install prices. Our heat pump costs guide and best heat pumps guide help choose.
Frequently Asked Questions
Get free heat pump quotes
Match with MCS-certified installers who take the Boiler Upgrade Scheme grant off the price in England and Wales, and get personalised quotes for your home. Free, no obligation, takes about 60 seconds.