Five reasons why air-to-air heat pumps might be the missing piece for decarbonising social housing
www.nesta.org.uk/blog/5-reasons-air-to-air-social-housing/
www.nesta.org.uk/blog/5-reasons-air-to-air-social-housing/
For most people, a heating system’s success is measured by comfort, control and running costs, not seasonal coefficients of performance. While air-to-water (A2W) heat pumps perform excellently in most settings, they are sometimes less suited to the needs of social tenants, which impacts trust and satisfaction. For some homes, air-to-air (A2A) heat pumps might provide a more responsive and intuitive to use solution to decarbonisation.
A2W heat pumps are a proven, efficient solution for decarbonisation, but there are some limitations when they are deployed in social housing and fuel poverty contexts.
Issues with installation and commissioning are not uncommon in government funded retrofit. Poor pipe lagging or incorrectly set heat curves can leave systems underperforming from day one. This can be further compounded by inadequate handover processes where tenants are left with technical manuals and little practical support on how to use the system efficiently.
Additionally, the low and slow nature of A2W heat pumps can feel counter-intuitive for those tenants who are used to energy rationing and focused on immediate bill reduction. As a result, many tenants, anxious about costs, frequently turn systems off and on. This stop-start approach reduces heat pump performance and drives up cost.
A2W heat pumps remain the cornerstone of UK home decarbonisation policy, but more work is needed to understand how to install these systems better in complex settings. This includes looking at how social housing providers procure these services to guarantee performance, and how handover processes can be redesigned to better empower tenants.
However, there is a subset of people, living in social housing, that could benefit from a fundamentally different delivery mechanism that aligns more closely with their lived realities.
Unlike A2W systems, which circulate heated water through radiators or underfloor pipes, A2A heat pumps extract heat from the air outdoors into a refrigerant and use that to warm up the air inside the home.
In some contexts, they could provide a more suitable alternative to decarbonising social housing. Here are five reasons why.
Fuel poor households tend to not heat their entire home continuously. Behaviours such as cold zoning (heating only the living room while leaving bedrooms cold to save money) or heating intermittently (turning the heating off and on at night or when away) can significantly affect A2W efficiency and running costs as well as fail to provide adequate comfort. In this instance, A2A systems might be more forgiving. By automatically increasing fan speeds to move heat quickly, they maintain high efficiency even during a rapid warm-up. They can deliver warm air in just three to four minutes, and could support zonal and intermittent heating behaviours without the same efficiency or comfort penalties and give more control to users.
Because radiators are less hot with A2W heat pumps, tenants often worry their heating is broken. A2A might solve this by providing immediate, tangible reassurance. It blows hot air almost instantly, confirming for the tenants that the home is indeed being heated and reducing call-outs and the need for tenant support.
To achieve good system performance, A2W installations require precise unit sizing, hydraulic balancing and setting of weather compensation curves, leaving room for installer error. A2A units are load compensated, meaning that the internal unit directly monitors room temperature and adjusts output automatically. Moreover, as the fan speed of internal units can modulate up and down, they might be more forgiving to sizing issues. This could reduce the risk of a system underperforming due to poor design or complex commissioning setups.
Installing a full A2W system often involves lifting floorboards and replacing radiators, which can be highly disruptive for elderly tenants or households in heavily furnished homes. A2A systems bypass the wet heating system entirely, offering a cheaper and less invasive retrofit option for those who cannot face a major home overhaul.
Dense social housing blocks are increasingly prone to extreme summer overheating. Over half of the poorest fifth of English families live in homes liable to get too hot, posing a serious health risk. Unlike A2W, A2A provides cooling alongside heating, which will be particularly useful as summers get hotter.
While A2A might offer some benefits over other alternatives, its property suitability presents both a limitation to at-scale deployment and a unique opportunity for decarbonising social housing. Rather than a silver bullet, A2A should be viewed as a specialised tool for specific archetypes where traditional wet systems are less suitable.
It is particularly well suited to flats and smaller dwellings, a housing type overrepresented in social housing compared with any other tenure, with 43% of homes being flats compared to just 9% of owner-occupied properties.
For the many fuel poor homes that still rely on inefficient storage heaters or direct electric systems, A2A offers a better, up to four times more energy efficient upgrade. Because it requires no internal plumbing, it can be installed with minimal disruption to the resident.
However, hot water remains a challenge. While A2W typically requires space for a hot water cylinder, most UK A2A systems do not provide hot water at all. This necessitates a separate standalone solution which, much like an A2W cylinder, can be difficult to site in small homes.
A2A heat pumps could be a critical tool for decarbonising our housing stock while simultaneously tackling fuel poverty. In the right settings, it could offer a more intuitive user experience, lower bills and improved comfort for tenants compared to A2W systems. However, more work is needed to understand how A2A is being used in the real world, particularly its energy performance when used for intermittent heating or summer cooling, and its potential for effective zonal control.
Nesta is currently exploring how to gather this evidence to help social housing providers make more informed decisions about home decarbonisation.
We would love to collaborate with others to explore this further. If you are a social housing provider or installer planning to deploy A2A, we would love to explore this further with you. Please get in touch with the team at [email protected]
