Air-to-air heat pumps: a big opportunity for UK installers?

Summary

Air-to-air heat pumps are gaining relevance in the UK domestic heating market as MCS moves to bring the technology into its certification framework. For installers, the opportunity is significant, particularly in homes where wet central heating retrofits are difficult, but success depends on correct heat loss assessment, system sizing, indoor unit placement, refrigerant competence, controls and commissioning. Certified air-to-air heat pumps give installers and customers independently verified performance data, supporting better product selection, compliance and confidence in low-carbon heating and cooling solutions.

Position of air-to-air heat pumps in the UK market

Air-to-air heat pumps are moving from the margins of domestic low-carbon heating into a more formal place in the UK market. With MCS updating its standards to bring air-to-air systems into scope, installers are likely to see growing interest from homeowners looking for efficient heating, comfort cooling and lower-disruption retrofit options.

For contractors, the opportunity is attractive but technically specific. These are not simply “air conditioners that heat”. Correct application depends on heat loss, air distribution, refrigerant design, condensate management, sound, controls, electrical supply and commissioning. MCS recognition adds another layer: installers will need to understand the competence expectations attached to certified installations.

How does air-to-air differ from air-to-water?

An air-to-air heat pump transfers heat between outdoor air and indoor air using a vapour-compression refrigeration circuit. In heating mode, the outdoor coil acts as the evaporator and the indoor unit rejects heat directly into the room. In cooling mode, the cycle reverses and the indoor unit removes heat and moisture from the occupied space.

This makes the design approach different from an air-to-water heat pump. There is no hydronic emitter circuit to balance and no radiator or underfloor heating flow temperature to optimise. Instead, comfort depends on indoor unit selection, fan performance, throw pattern, room geometry and control strategy. Most systems provide space heating and cooling, with new technological advances increasing the number of heat pumps that also provide domestic hot water (DHW).

Typical domestic configurations include single split, multi-split and, in larger homes or light commercial applications, small variable refrigerant flow (VRF) systems. The main components are the outdoor unit, one or more indoor fan-coil units, refrigerant pipework, insulated condensate drains, controls, isolators and suitable electrical protection.

The technology is not new: reverse-cycle air conditioners have provided heating in homes for many years. What is changing is the recognition of air-to-air heat pumps within the UK’s renewable-energy certification and incentive landscape.

Air-to-air is particularly suited to dwellings without wet central heating, electrically heated homes, flats, extensions, garden rooms, converted lofts and open-plan areas where rapid response is desirable. It can also support summer resilience as overheating becomes a more common concern.

What are the design considerations for installers?

An important stipulation for MCS is the requirement for whole building heating. The starting point therefore remains a room-by-room heat loss assessment. Capacity should be checked at relevant outdoor design conditions, not only at nominal catalogue points. Installers should also consider minimum modulation, part-load operation and the likelihood of cycling in smaller rooms. Oversizing may deliver fast warm-up, but it can reduce comfort, increase noise and shorten run times, leading to lack of performance, and increased running costs.

Indoor units should be positioned to wash air across the occupied zone without blowing directly at seating or sleeping areas. Ceiling height, furniture layout, door positions and stairwells all affect air movement. Poor indoor unit positioning can lead to many issues including draught complaints, cold spots or stratification. In multi-room properties, installers should avoid assuming that one high-wall unit will heat a whole dwelling evenly. Zoning, door closure and internal heat transfer need to be discussed clearly with the customer.

Refrigerant pipework is another critical area. Pipe length, height difference, added charge, insulation, flare quality, pressure testing, evacuation and leak checking must follow the manufacturer’s instructions and F-gas requirements. Condensate should be designed for both cooling and defrost conditions, with suitable fall, insulation where needed, and consideration of freezing risk or nuisance discharge.

Outdoor units require adequate airflow and service access, with attention to recirculation, prevailing wind, snow or leaf build-up, wall vibration and neighbour noise. Sound power data should be reviewed during selection, while sound pressure at sensitive locations will depend on distance, reflections, mounting and operating mode. Electrical design should confirm circuit capacity, protection, isolation and any DNO notification requirements.

Controls are equally important. Set-points, fan modes, timers, occupancy patterns, zoning and remote access can make the difference between an efficient system and one that acts like an oversized electric heater. At handover, installers should explain realistic heat-up times, filter cleaning, defrost behaviour, cooling/dehumidification, and if required, when the separate hot-water system will operate.

What do the MCS changes mean?

MCS has been updating its heat pump standards to explicitly cover air-to-air heat pump products and installations. Its December 2025 update introduced air-to-air requirements into the Heat Pump Product Standard MCS 007, the Heat Pump Pre-Sale Information and Performance Calculation documents, and the heat pump design standard. MCS has also stated that technical supervisors for air-to-air heat pump installations must hold Level 3 or above competence in Refrigeration, Air Conditioning and Heat Pumps (RACHP).

That competence requirement is significant for the sector. Air-to-air systems use refrigerant circuits operating at higher pressures than hydronic systems and may involve refrigerants with flammability, toxicity or high-pressure considerations. RACHP skills are therefore central to safe installation, commissioning and maintenance.

How do you use certified data?

For installers, certification is most useful when it improves the quality of technical selection. Product data should be checked for heating capacity, COP, SCOP, sound power, application limits and low-temperature performance. Seasonal figures help comparison, but the installed result will still depend on sizing, controls, defrost, fan operation, maintenance and occupant behaviour.

A certified product is not a shortcut around design. It simply gives the installer a more reliable basis for comparison, design and compliance. The product must still be suitable for the building, installed to the manufacturer’s instructions and correctly commissioned.

MCS certification should also be understood in context. It may be required for funding routes or customer assurance, but it does not replace Building Regulations, planning constraints, electrical requirements, F-gas obligations, product safety rules or good practice.

Where does Eurovent Certification fit in?

At product level, MCS 007 covers single heat pumps up to 45 kW, including electrically driven heat pumps designed to provide space heating and, where applicable, domestic hot water. Certification involves more than accepting a manufacturer’s catalogue data. It involves laboratory testing and factory audits, verifying product performance and quality of manufacturing.

Eurovent Certification is one of the bodies offering certification services for MCS 007 heat pumps. Its role is to assess products against the scheme requirements, manage testing and audit activity, and support publication of approved performance data for certified models. For manufacturers selling across Europe, Eurovent Certification also offers a coordinated route that can align MCS 007 with other schemes such as Eurovent Certified Performance, Heat Pump Keymark and NF 414, utilising one test result for all schemes. This removes the need for retesting, reducing timescales, and costs for manufacturers.

MCS is primarily an installer certification scheme, set up to protect the consumer (homeowner) and ensure they receive high-quality installations that perform as expected. The installation must therefore be designed, installed and commissioned by an appropriately certified contractor, in accordance with the applicable MCS standards and the manufacturer’s instructions. The precise requirements for air-to-air systems should be checked against the latest MCS publications and product listings.

Final thoughts

For installers, the end benefit is practical: independently assessed product data that can support selection, compliance and customer confidence. As air-to-air heat pumps become more visible in the domestic market, the winners will be those who combine technical competence with careful design, clear handover and robust use of certified performance information.

FAQ

What is an air-to-air heat pump?

An air-to-air heat pump transfers heat between outdoor air and indoor air using a refrigeration cycle. In heating mode, it delivers warm air directly into the occupied space via indoor fan-coil units. In cooling mode, the process reverses, helping to remove heat and moisture from the room.

Why should installers pay attention to air-to-air heat pumps?

They can offer an efficient, lower-disruption option for homes without wet central heating, flats, extensions, loft conversions and open-plan spaces. With MCS progressing the inclusion of air-to-air heat pumps, installers who understand the technical requirements will be better placed to meet growing demand.

Why choose certified air-to-air heat pumps?

Certified air-to-air heat pumps provide independently assessed performance data, helping installers compare products, support compliance and give customers greater confidence in the declared efficiency, capacity and quality of the system selected.

How can manufacturers apply for MCS certification?

Eurovent Certification provides a one-stop-shop for heat pump certification, offering MCS 007, Eurovent Certified Performance, heat pump KEYMARK and the NF mark for heat pumps and hybrid heat pumps. Manufacturers wishing to apply for more than one mark can access a streamlined certification process that combines all the required laboratory tests and factory audit requirements for multiple marks into one test campaign – reducing duplication, admin and costs.

If you are a manufacturer wanting to know more about UK heat pump certification you can email UK Partnership Manager, Matthew Nudd at m.nudd@eurovent-certification.com

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