Air-to-air systems are air-source heat pumps where the useful heat is distributed into a building as warm air rather than warm water, which is used in radiators and underfloor systems. Such air-to-air systems are already extremely common in commercial settings, and in certain countries, including the Nordics and the United States. So-called ‘reversible’ air-to-air systems can produce space cooling as well as heating. As cooling demand grows, there is therefore potential for the growth in demand for cooling to organically grow the use of these reversible air-to-air systems for heating.

For buildings with existing wet central heating systems like the majority of those in the UK, however, air-to-air systems may only have limited value, unless cooling is required. Even in this case though, a separate cooling system in addition to a heating system may be most logical for practical reasons. The use of air-to-air systems seems likely to have most value in small dwellings, those without wet central heating, and those where cooling is required.

Energy policymakers working on the decarbonisation of the building stock will want to keep a close eye on the potential for air-to-air systems to speed up building decarbonisation. The added benefit of cooling could provide a strong consumer pull, and air-to-air systems are already likely to have cost and decarbonisation value in some homes. While increased policy support for air-to-air systems could be considered, such support needs to reflect:

• The heterogeneity of air-to-air systems; they range from freestanding units to whole-house systems that also produce hot water.
• The fact that they can be extremely cheap to install depending on the type of system.
• The fact that building owners’ interest in them may primarily be for cooling.

As such, we make three policy recommendations which could support air-to-air heat pump systems while protecting public budgets from the risks of gaming and maximising the value of public spending:

• Grant funding and other market support could be made available for air-to-air systems subject to careful consideration and limits.
• Planning permission policy could be reformed to ease the installation of air-to-air systems.
• Energy price rebalancing could support the economics of air-to-air systems.