Air-source vs ground-source heat pumps: which one fits your home?

Heat pumps come in two main flavours. Air-source (ASHP) pulls heat out of the outside air and upgrades it. Ground-source (GSHP) pulls it out of the soil via a buried loop of pipe. Both qualify for the £7,500 Boiler Upgrade Scheme grant. Both, when designed properly, will replace a gas or oil boiler beautifully. But they aren't interchangeable — and the right choice depends far more on your site than on personal preference.

Air source vs ground source — the headline differences

How each kind of heat pump actually works

An ASHP looks a bit like a large outdoor air-conditioning unit, usually sitting on an exterior wall or a small base beside the house. A refrigerant circuit absorbs heat from the outside air — yes, even well below freezing — and a compressor upgrades it to useful radiator or cylinder temperatures. All the working kit lives in one box outdoors.

A GSHP runs the same refrigerant cycle but draws its heat from a glycol-water mix circulating through a buried pipe loop. That loop is either a set of vertical boreholes drilled 50–150m deep, or a horizontal array in a trench field. The compressor itself sits inside the house — usually tucked into a utility room or a dedicated plant room — so there's no outdoor fan.

Which heat pump suits which home

Air-source is usually the right call if:

• You have a typical domestic plot with a limited garden — terraced, semi-detached or new-build homes.
• Your budget is tight and you want the lowest upfront number after the BUS grant lands.
• You're on mains gas and need a reasonable payback window for the swap to make financial sense.
• The install needs to happen in weeks, not months — for example in a boiler emergency over the winter.
• You value simpler maintenance and a proven, high-volume service network across the UK.

Ground-source is usually the right call if:

• You have a large plot — 800 m² or more for a trench field — or you can drill boreholes on the drive.
• You're building new or doing a major renovation. Ground works are much cheaper when the diggers are already on site.
• You need the highest possible efficiency in a big, well-insulated home that you plan to live in for 20+ years.
• Silence matters to you. Ground-source has no outdoor fan unit at all, so there's nothing to hum beside the patio.
• You're off-grid and running on oil, LPG or Calor — the lifetime running-cost saving pays back the higher upfront.

Running costs — the bit that actually matters over 20 years

Ground-source is more efficient because the soil is a far more stable heat source than the air — roughly 8–12°C year-round in the UK, compared with winter air that can drop to -5°C. That higher, steadier source temperature translates directly into a better seasonal COP (SCOP) and a cheaper cost per useful kWh of heat in your radiators.

Here is the headline. On a dedicated heat-pump tariff, a well-designed GSHP is genuinely the cheapest heating you can buy in the UK — including gas. On a standard tariff, the gap to ASHP narrows to around £300 a year, which won't recover the £15k+ of extra upfront cost inside the system's lifetime. The tariff matters as much as the kit.

The £7,500 BUS grant applies equally to both

The Boiler Upgrade Scheme now pays the same £7,500 across ASHP and GSHP. That's a big shift from the old RHI days, when GSHP paid out roughly twice as much. The policy change has tilted the economic case firmly towards air-source for most homes, because ASHP is cheaper to buy AND attracts the same grant. Ground-source has to earn its place on site conditions alone.

How OMEGA designs a heat pump that actually works

1. Full heat-loss survey to MCS MIS 3005 — measured room by room, never just estimated from the EPC.
2. Fabric-first review. Where it matters, we recommend insulation upgrades before the pump so the system is sized correctly.
3. Correct sizing from day one. Oversizing is the single biggest cause of unhappy heat-pump customers — we don't do it.
4. Weather compensation tuning and low-flow-temperature design (45°C or below) for a quiet, efficient, comfortable home.
5. BUS application handled for you end-to-end — you never see a form, and the £7,500 comes off your invoice before you pay.

If you'd like a straight answer on whether your home is heat-pump ready, book a free suitability survey online or ring 0800 229 4094, Monday to Saturday. Our surveyor will tell you honestly whether a fabric upgrade should come first, whether a hybrid or A-rated boiler is the smarter bridge, or whether you're ready to go. No cost. No obligation. No pressure.