A key benefit of air-to-air heat pumps is their ability to be used well for different heating patterns and with a variety of different system configurations. For example, some choose to install an indoor unit in each room as they prefer to keep doors closed or use their heating in a zoned or intermittent manner.

Others may install only two indoor units for the whole home. One might be used to heat the whole of an open-plan downstairs kitchen and living space. The other might be installed on the upstairs landing to heat all rooms on the first floor, by leaving doors to rooms open. Some homeowners have even reported that a downstairs unit can provide ample heat to the rooms upstairs in most contexts.

So the system design requirements for an air-to-air heat pump to be eligible for the grant mustn’t limit how systems can be installed, as this could drive up both cost and complexity.

One limitation is that most models don’t usually provide hot water, so a separate system is needed. However, the air-to-air heat pump grant should support flexible solutions, including heat batteries and other low-carbon options.

Currently, many homeowners installing air-to-air heat pumps choose to retain their boiler for hot water use. Some may not know what the other options are, whilst others may want to wait until their boiler needs to be replaced. However, this leaves homes in a situation where roughly a quarter of their heat demand is still burning fossil fuels.

That’s why it’s positive to see that heat batteries are also eligible for the new £2,500 air-to-air heat pump grant. This could encourage homeowners to fully decarbonise their heat demand in situations where their installations would become unaffordable, or more expensive than a post-grant air-to-water installation, if they were to decarbonise their hot water too.

However, the grant's scope should ideally be wide enough to include other domestic hot water supply options, such as a hot water heat pump, or even immersion heaters if they’re used alongside an air-to-air system. This would provide stronger support for the low-carbon heating transition by enabling homes that are installing air-to-air heat pumps to more easily take the final step in fully decarbonising their systems.

There is a risk that planning constraints are a major barrier to adopting the system,, particularly in flats or non-detached properties. Expanding permitted development rights will be key to ensuring the grant is widely accessible.

In November 2024, the UK government updated planning rules to include heat pumps under permitted development in England, in particular dropping the “one metre rule” and allowing units that provide cooling alongside heating.

However, only detached homes are able to have two outdoor units under permitted development, with all other property types requiring planning permission for additional units. This isn’t an issue for air-to-water, where it’s relatively unlikely that multiple outdoor units would be required for non-detached homes, but it could pose a challenge for air-to-air, particularly in buildings with multiple homes, such as flats.

This is because air-to-air systems are more likely to require two outdoor units to avoid complex, efficiency-reducing, impractical or aesthetically undesirable refrigerant pipe runs to reach all indoor fan coil units.

That’s why the UK government should consider expanding permitted development for two outdoor units to other property types.

There are also permission constraints for some properties where air-to-air heat pumps are particularly well-suited, such as flats.

For example, leaseholders in flats will usually require freeholder consent to install an air-to-air heat pump, due to either structural changes or external additions to the building. Coupled with the permitted development rights of only one outdoor unit per property, and concerns over the peak load capacity for electricity within the building, this can make it extremely difficult for those in flats to install an air-to-air heat pump and benefit from the grant. The Leasehold and Freehold Reform Act 2024 provides an opportunity to help reduce challenges associated with freeholder consent, especially as many aspects of this act will still require secondary legislation and consultation.

Although the £2,500 of funding available through the air-to-air heat pump grant is roughly commensurate with the lower cost of installation, it’s important to consider what the actual savings will end up being for homeowners.

Air-to-air heat pump systems aren’t currently installed under the Microgeneration Certification Scheme (MCS). However, installations eligible for the pump grant through the Boiler Upgrade Scheme (BUS) will likely require MCS certification. This is important to ensure the government grant has controls around quality; however, it can increase both financial and administrative costs for installers, potentially reducing the overall savings a homeowner would achieve from a BUS-eligible air-to-air heat pump installation.

Given that air-to-air heat pumps are usually installed with a less intensive heat loss survey, and that they are generally more forgiving in terms of performance, efficiency, user operation and comfort than air-to-water heat pumps, it’s worth considering whether the MCS process could be made less intensive or costly for air-to-air heat pump systems, without compromising on quality. This could allow homeowners to make more efficient use of the grant and maximise the value of government funding.

Making a £2,500 air-to-air heat pump grant available for air-to-air heat pumps or heat batteries will help boost the number of homes able to switch to low-carbon technology. This will be achieved by building public awareness, increasing access to more flexible and appealing solutions, and giving households that may face complex air-to-water installations an alternative route to decarbonisation.

However, the issues described above will be important to address if the grant is to be used most effectively and deliver widespread adoption of air-to-air heat pumps across the UK.

An air-to-air heat pump typically costs between £1,500 and £4,000 per unit in the UK, depending on system size and installation complexity. The grant can help reduce upfront costs.

Yes, the UK government is introducing an air-to-air heat pump grant to support the installation of low-carbon heating systems.

It provides energy-efficient heating and cooling, lower carbon emissions, flexible zoned heating, and lower installation costs compared to other systems.

Homeowners may be eligible for the air-to-air heat pump grant through the Boiler Upgrade Scheme (BUS), offering up to £2,500 towards installation.

You can apply for the grant through an MCS-certified installer, who typically handles the application process on your behalf.

Eligibility for the air-to-air heat pump grant generally includes homeowners in England and Wales replacing fossil fuel heating systems, subject to property and installer criteria.