Air to air heat pumps: how they work and the £2,500 grant

Checked November 2026

An air to air heat pump heats your rooms by blowing warm air from indoor units on the wall. It doesn’t heat your water. Since 28 April 2026 the law allows a £2,500 Boiler Upgrade Scheme grant towards one in a home. When we checked in November 2026 though, MCS said no installers were certified to fit them under the scheme yet. So the grant is in law, but check with your installer that they can actually claim it before you sign anything. That goes for us too.

On cost, we haven’t put a figure here on purpose. The prices you’ll find online are mostly old or guessed. What you pay depends on how many rooms need a unit and how far the pipe runs are.

What is an air to air heat pump?

It’s a heat pump that moves heat from the outside air into your rooms as warm air. The outdoor unit sits on a wall or on the ground. Refrigerant pipes run through the wall to one or more indoor units, usually mounted high up on a wall. A fan in each indoor unit pushes the warm air into the room.

MCS describes them as working in a similar way to air to water heat pumps. The difference is how the heat gets delivered. There are no radiators, no water pipes and no hot water cylinder involved. Each indoor unit heats the room it’s in, plus whatever open space is around it.

You can have one outdoor unit feeding a single indoor unit. Or one outdoor unit running several indoor units in different rooms. That’s usually called a multi-split. Which one you need comes down to the layout of the home and how much heat each room loses.

Is an air to air heat pump the same as air conditioning?

Not quite. If you’ve seen an air con unit on a wall, you know what an air to air heat pump looks like. The kit is often very similar. Most air to air heat pumps can cool on a hot day. Plenty of air con units can heat.

What separates them, for the grant at least, is what the system is designed to do. MCS says an air to air heat pump must be optimised to heat the whole property. It can cool as well. But systems that only cool are excluded from MCS, and so from the grant.

Planning follows the same line. In England, an air source heat pump on a house can usually go in under permitted development, but those rules don’t cover a unit that’s used only for cooling. Our guide to heat pump planning permission has the details. So if what you really want is a cool bedroom in July, that’s air conditioning. It’s a perfectly good thing to have. There’s just no grant for it.

We do air conditioning installation as well, so we’re happy to talk through either. The honest question is what you’re mainly after. Heating or cooling.

How is air to air different from an air source heat pump?

Most people who say “air source heat pump” mean an air to water one. It heats water instead of air. That water goes round radiators or underfloor heating, and it also heats a hot water cylinder for your taps and shower.

Here’s how the two compare on the things people ask us about most:

	Air to air	Air to water (air source)
How it heats	Warm air from wall units	Hot water through radiators or underfloor heating
Hot water	No	Yes, with a cylinder
Boiler Upgrade Scheme grant	£2,500, homes only	£7,500, or £9,000 replacing oil or LPG off the gas grid
Can cool	Usually	Not usually

Grant figures from Ofgem and the GOV.UK grant notice, checked November 2026.

Air to air stays at £2,500 in every case. The £9,000 rate is only for air to water and ground source heat pumps replacing oil or LPG, and Ofgem says it runs until 31 March 2027.

An air to water system is a bigger job. It ties into your radiators and needs space for a cylinder. But it replaces your boiler completely, heating and hot water both. Our guide to air source heat pump cost shows what goes into that price. An air to air system is simpler to fit in some homes. It leaves you needing another way to heat water though.

Can I get the £2,500 air to air grant?

Not yet, as far as we can tell. The grant is £2,500 off the cost of an air to air heat pump. It’s for homes only. The change came in through the Boiler Upgrade Scheme (England and Wales) (Amendment) Regulations 2026, which took effect on 28 April 2026. Those rules exclude non-residential buildings from the air to air grant.

The usual scheme rules still apply, so you need to own the home and be replacing fossil fuel heating, and GOV.UK counts oil, gas, LPG and electric heating. There are further rules on timing, new builds, social housing and earlier heat pump funding, set out in the Boiler Upgrade Scheme conditions.

The grant isn’t paid to you directly. An MCS certified installer applies for it and it comes off your quote. That’s the sticking point right now, and this is where it gets messy. The law changed in April 2026. But to claim the grant an installer needs MCS certification for air to air. When we checked on 3 November 2026, MCS’s own page for homeowners still listed air to air as “coming soon”. It said no installers were yet certified to fit them.

MCS’s latest update, from 8 September 2026, explains why. The certification bodies that check installers have to be accredited for air to air first. Only then can installers apply. MCS said the timeline for that is outside its direct control. Ofgem’s scheme page lists the £2,500 but doesn’t say claims are open.

So our advice is simple. If an installer quotes you with the £2,500 taken off, ask to see their MCS certificate and check it covers air to air heat pumps. If it doesn’t, the grant can’t be claimed through them. We’ll update this page when that changes.

One more thing to ask about. If your boiler does your hot water now and you want to keep it for that, ask how the grant rules treat it. We haven’t seen that case spelt out clearly in the official guidance.

When is air to air the right choice?

It suits some homes really well and others not at all. We’d look at it seriously where:

The home has no radiators. Lots of flats and some older houses run on electric storage heaters or panel heaters. Putting in a full wet system with radiators and pipes is a big, disruptive job. Air to air skips that.

The home is smaller. Nesta’s research says air to air may be a good option for smaller properties and flats. It also says costs rise sharply for larger homes. That matches what you’d expect. More rooms means more indoor units.

You want cooling too. If the heat pump is mainly for heating but a cooler summer bedroom would be welcome, air to air does both.

Where we’d usually steer you away from it is a family house that already has radiators and a cylinder. In that home an air to water heat pump uses what’s there, does your hot water and gets the bigger grant. Air to air would leave you sorting hot water separately. Our guide on whether your home suits a heat pump covers the other things to check.

Heating just one room, like a conservatory, is another case. MCS says the system must be designed to heat the whole property. So a single unit in one room won’t qualify for the grant. It might still be worth doing. Just go in knowing there’s no £2,500 off.

Does an air to air heat pump heat water?

No. MCS says many don’t, and Nesta’s report says they can’t produce hot water and need a separate system alongside them, such as an immersion heater.

In practice that means a hot water cylinder heated by electricity, or another water heating setup. That needs space and it adds to the cost. Factor it in from the start. It’s the part people most often miss.

If you’d rather have one system that does heating and hot water, an air source heat pump installation with an air to water heat pump is usually the better fit.

Frequently asked questions

Can I get an air to air heat pump for a flat?

Often, yes. Flats are one of the places it makes most sense, especially ones without radiators. For the grant you’d need to own the flat and meet the other scheme rules. The outdoor unit has to go somewhere too. Under permitted development in England, the outdoor unit on a flat can’t be bigger than 0.6 cubic metres. If you’re a leaseholder, check your lease and talk to the freeholder before anything goes on an outside wall.

What does an air to air heat pump cost to run?

It depends on how much heat your home needs, how efficient the unit is and what you pay for electricity. We’d rather not give a number that won’t match your home. Nesta notes they should be about as efficient as air to water heat pumps, but that this isn’t well documented in the UK yet. A proper survey of your home is the only way to get an estimate worth trusting.

Not sure which type of heat pump suits your home? We’ll look at it properly before anyone talks prices. Book a free home assessment

Sources

• Ofgem, Boiler Upgrade Scheme (BUS), checked 3 Nov 2026, www.ofgem.gov.uk
• GOV.UK, Notice of approved grant categories and values for the Boiler Upgrade Scheme, checked 2 Nov 2026, www.gov.uk
• legislation.gov.uk, The Boiler Upgrade Scheme (England and Wales) (Amendment) Regulations 2026 (SI 2026/390), checked 3 Nov 2026, www.legislation.gov.uk
• GOV.UK, Apply for the Boiler Upgrade Scheme: check if you’re eligible, checked 3 Nov 2026, www.gov.uk
• MCS, Air-to-air heat pumps (consumer page), checked 3 Nov 2026, mcscertified.com
• MCS, Implementation of air-to-air heat pumps into MCS enters next phase (8 Sept 2026), checked 3 Nov 2026, mcscertified.com
• Nesta, Domestic heating technology options: air-to-air heat pumps (Feb 2025), checked 3 Nov 2026, www.nesta.org.uk
• legislation.gov.uk, GPDO Schedule 2 Part 14 Class G (air source heat pumps), checked 2 Nov 2026, www.legislation.gov.uk