Air-to-Air vs Air-to-Water: Which Heat Pump Grant?

Two heat pumps, two very different grants, and a lot of confusion about which is which. If you have seen a £7,500 figure and wondered why the air-to-air quotes you have been given only mention £2,500, this guide is for you. The short version: they are two separate technologies under the same Boiler Upgrade Scheme (BUS), and the right one for you depends far more on your home than on the size of the grant.

We will walk through both grants honestly, then match them to real home types. As at July 2026, these are the figures direct from gov.uk and the underlying regulations (SI 2026/390).

The £9,000 off-gas uplift — and why air-to-air can't touch it

From 21 July 2026 to 31 March 2027, homes off the mains gas grid that heat with oil or LPG can access an enhanced grant of up to £9,000 — but only for air-to-water or ground-source. Air-to-air is explicitly excluded from this uplift. So if you are an off-gas oil or LPG household weighing the two, the maths often tilts hard towards air-to-water: a much larger grant, plus hot water included. We would rather tell you that plainly than sell you the wrong system.

Which grant suits your home?

All-electric homes, flats and storage-heater properties

This is where air-to-air genuinely shines. If you heat with storage heaters or direct electric, air-to-air delivers heat at roughly 6.5p/kWh (SCOP 4.0) against about 15p from storage heaters on Economy 7 or 26.11p from direct electric, using the Ofgem cap for 1 July–30 September 2026. A realistic saving versus storage heaters is around £500–£900 a year — not the "70% off" some sites claim, because storage ran on cheap night units. Add the £2,500 grant, a low install cost, and summer cooling, and for many flats and park homes air-to-air is the sensible pick. Keep your existing immersion or cylinder for hot water.

Off-gas oil or LPG whole-house heating

Here we usually point you away from us. Air-to-water is the stronger candidate: the £7,500 grant (up to £9,000 during the off-gas window), whole-home heating, and hot water in one system. Air-to-air can still make sense for a specific room or an annexe, but as a whole-house replacement for oil or LPG, air-to-water typically wins on both grant and coverage.

Mains gas homes

Be realistic. Against mains gas at 7.33p/kWh, air-to-air running costs are roughly at parity — you will not dramatically cut your heating bill. The honest reasons to fit air-to-air on gas are the £2,500 grant, low install cost and, above all, cooling. If beating gas on running cost is your only goal, neither heat pump is a slam-dunk, and air-to-water's higher spend is harder to justify.

Homes that specifically want cooling

Only air-to-air cools. If summer comfort matters as much as winter heating, air-to-water is off the table and air-to-air is your route — with the bonus of the £2,500 grant provided you also meet the eligibility rules below.

Scotland and Northern Ireland

Neither grant applies. BUS is England and Wales only. Home Energy Scotland excludes air-to-air (it requires a system providing 100% of heating and hot water), so in Scotland air-to-air gets 0% VAT and nothing more; air-to-water may qualify for Scottish support. Northern Ireland has 0% VAT only. Wales does get the £2,500 BUS grant, plus means-tested Nest support that typically funds air-to-water.

The catch nobody else mentions

Whichever technology you choose, both grants require an MCS-certified installer and an MCS-certified product. That is where air-to-air has a real-world snag: MCS air-to-air certification is still rolling out through 2026. Certification bodies are still gaining UKAS accreditation to certify air-to-air installers, technical supervisors need RACHP Level 3, and MCS has given no fixed completion date. The £2,500 grant is real and in law — but MCS-certified air-to-air installers are scarce in mid-2026, and no MCS-certified air-to-air job means no grant. Air-to-water, by contrast, has a mature MCS installer base you can access today. If you need the grant paid this year, that availability gap is worth weighing.

How to make the call

Start with your heating fuel and your hot water, not the grant size. If you are all-electric or on storage heaters, want cooling, or live in a flat, air-to-air and its £2,500 grant is usually the honest fit — just confirm your chosen installer holds live MCS air-to-air certification before you sign. If you are off-gas oil or LPG and want one system for heating and hot water, air-to-water's £7,500 (up to £9,000) will very likely serve you better, and we will happily say so. When you are ready, we can connect you with an MCS-certified air-to-air installer and give you a straight answer on whether the grant is claimable in your area yet.