A few weeks ago, the temperature record in England was broken, hitting 37.7°C in Lingwood in Norfolk on 26 June. In early July the Met Office declared another heatwave, with temperatures set to again breach 30°C in much of the country for up to a week.

As Britain bakes under scorching sunshine and sweats through back-to-back ‘tropical’ nights, it’s fair to say that most households aren’t thinking about how best to warm their homes.

Instead, conversation turned quickly to air conditioning: why so few UK households have it; how many schools, hospitals and workplaces lack cooling technology; and what all this might mean for education, health and productivity as the country continues to face more extreme temperatures.

But here’s the thing. In certain settings, cooling and heating can be achieved using exactly the same technology. In particular, a built-in split system air conditioning unit is just an air-to-air (A2A) heat pump. And if installed correctly, such systems can provide low-carbon heating to homes over winter and then cool them during summer. The same hardware that could have offered respite from this year’s blistering heatwaves could then create a cosy refuge come Christmas.

Let’s start by looking at air conditioning in the UK, and how it compares with other countries around the world. At a glance we are miles behind. According to research by the Energy Demand Research Centre, just 4.3% of homes in England have AC. The share is 16% in Brazil, 24% in France, 60% in China, and as high as 91% in Japan.

Much of this discrepancy is down to historical choices concerning our housing stock. In the mid 20th century the UK moved away from ‘town gas’ (made by distilling coal or oil) to relatively cleaner natural gas from the North Sea. In 1963, around 70% of UK homes were heated by coal. By 1977, nearly half of homes had ‘wet’ central heating, using networks of pipes to supply hot water to radiators throughout the building.

A few decades ago this made a lot of sense. Wet heating systems work well in cold climates, and are safer and more efficient than coal fires or wood-burning stoves. The same hot water can also be used for washing dishes and running baths. With cold winters and mild summers, Britain’s wet heating systems did the job well.

But elsewhere in the world, air-based systems (or HVAC) are more common. These circulate warm (or cool) air around the house through vents or wall-mounted units. These HVAC systems don’t typically heat the property’s water, with most homes opting for a separate unit to do this.

As the UK starts to experience more frequent and more extreme temperatures, consumer demand for cooling technology looks set to surge. In fact, researchers from the University of Manchester argue that cooling demand could increase by as much as 140% by 2050. Indeed, recent market analysis forecasts that the domestic air conditioning sector could grow by around 6% year-on-year between 2026 and 2034 (although this projection also includes commercial buildings).

This is hardly surprising. According to the Met Office, seeing a 40°C summer day in the UK is about 20 times more likely than it was in the 1960s, and within the next decade, it is possible that average daily highs could exceed 28°C for entire months in England.

We are starting to see signs of this corresponding change in consumer demand playing out in the data. While there is no centralised record of air conditioning installs in the UK – unlike with MCS for air-to-water (A2W) – we can get clues from survey data. According to analysis by USwitch, the share of UK homes self-reporting to be using air conditioning has doubled in three years. Of course, these figures should be interpreted with plenty of caution, as each survey only includes a few thousand residents. Even so, the overall trend implies an increase in demand for cooling technologies following several hot summers.

The surveys include both portable and built-in air conditioning. Portable AC systems tend to be single hose mobile units that draw air from inside and use it to cool other room-drawn air which is then expelled into the room. Hot air is expelled outside through the hose (you often see these poking out of windows or doorways). Portable systems are rarely used for heating, are much less efficient (partly due to negative pressure in the room which draws in hotter air from outside or from adjoining rooms), and tend to be noisier than the built-in alternative.

Built-in systems are essentially A2A heat pumps with a reversing valve, and include fixed indoor and outdoor components. To cool a room down, a cold liquid refrigerant inside the heat pump absorbs indoor heat, lowering the air temperature. This ‘absorbed heat’ converts the liquid into gas, which is then squeezed through the outdoor compressor, raising the temperature of the (now gas) refrigerant. A fan then uses outside air to transfer the heat contained in the refrigerant outdoors. Finally, an expansion valve drops the refrigerant's pressure again, re-freezing it (into a liquid again) to restart the cycle.

Looking at the use of desktop fans tells a similar story to air conditioning. Since 2022, the share of households self-reporting to be using fans has more than doubled, climbing from 14% to 34%.

Within the USwitch survey figures, what we are most interested in are the built-in units. Since 2022, the share of households reporting to have what is basically an A2A heat pump has increased from about 3% to 7%. Under the right conditions, many of these units could also be used to heat these people’s homes during the winter (although this is not always the case).

Perhaps surprisingly, many people might not even know that their air conditioning set-up can also serve as a home heating solution. As Ed Conway flags in a recent Substack article, the official Ofgem advice on A2A systems fails to mention that these systems can double up as air conditioning.

In some cases, households may have an AC unit for a couple of bedrooms which they only use in the summer, plus an entirely separate gas-powered wet heating system for the rest of the property which they use for the colder months of the year. This is a missed opportunity for home decarbonisation.

As the UK starts to experience more and more uncomfortably hot spells, the extra pay-off of an A2A system could help encourage people to swap out their gas boilers (at least for their heating). A replacement set-up that is as cheap to run in winter but also keeps you cool in summer – what’s not to like?

One answer is the current price. While often a cheap option for smaller homes and flats, air-to-air systems can be fairly expensive to install for larger homes. A rough estimate for a split-system feeding multiple rooms is anywhere between £1,500 and £2,700 per room. So, for a three bedroom house where heating (or indeed cooling) is also required in a single open plan living area, the upfront cost could be between £6,000 to £10,800.

The current home heating policy landscape offers limited support for A2A customers. Like with A2W heat pumps, there are set to be grants available, but they are comparatively modest (at £2,500 compared with £7,500 for A2W) and were only announced in November 2025 – three years after the A2W scheme launched.

Running costs on the other hand depend on how the system is used. At current energy pricing, the costs are likely to be lower than using an oil boiler and similar to a gas boiler or an A2W heat pump with a standard electricity tariff. But if you use a special heat pump tariff it could make an A2A system cheaper to run than a gas boiler.

There is also the question of housing suitability. For example, properties with very limited external space may struggle to accommodate the outer component of the built-in unit. Properties with a high number of separate rooms (like traditional Victorian terraced houses) or with poor insulation may also not be ideal for an A2A heat pump.

Strict leaseholds which prohibit external alterations can also present a barrier. Indeed, as it stands, only detached homes are able to have two outdoor units under permitted development, with all other property types requiring planning permission for additional units.

For many years, ensuring homes (and other spaces) are at a comfortable temperature in the UK has mainly involved designing heating systems. With its historically cold and wet climate, a well designed home, school or workplace used to be one that could simply be kept warm. But as set out above, cooling is increasingly important – just look at the recent survey evidence for fans and AC units.

Extreme heat has several major impacts on human wellbeing. As Hannah Ritchie explains in an article for Our World in Data, it reduces productivity, makes it harder for children to learn at school, and squeezes healthcare systems. At worst, she warns, it kills.

Starting with work, research published back in 2006 shows that productivity in office-based work follows an ‘inverted u shape’ as temperature increases. People are less efficient if they are shivering away at their desks, but also see relative workplace performance dip once the room heats up beyond 22°C.

So, as well as offering a home decarbonisation solution, A2A systems could also help support productivity in a warming climate. And with more people now working remotely than in 2006, the curve shown above arguably applies to people’s homes as well as their offices.

Turning to education, there is clear evidence that an uncomfortably hot classroom hampers learning outcomes. During last month’s sweltering weather, around 1,000 schools closed or shut early across England and Wales in efforts to protect both teachers and pupils from the worst of the conditions.

Sending children home is disruptive for parents and guardians (and might not even spare them from the discomfort of extreme heat in many cases), but keeping them in a stifling school also harms learning. Research from India shows even a 0.64°C increase in classroom temperature reduces exam pass rates by 3%. The negative effect surges once temperatures reach 40°C.

Finally, health is directly under threat from extreme heat. According to the World Health Organization (WHO), high temperatures can ‘disrupt and compromise essential health services’.

One way to get a measure of the challenge is to look at how the UK has performed during recent heatwaves compared with other countries. Analysis by The Centre for British Progress shows that during the 2022 heatwave, around 3,000 people in the UK died as a result of the elevated temperature. Heat-related death rates in the UK were over 10 times those in Sweden, and were twice as high as in the Netherlands (which has a similar climate to Britain).

The challenge was particularly acute in the UK’s cities: "London's rate of heat-related deaths exceeded any other northern European capital city, and were similar to those in Rome", the report shows. Crucially, air-conditioning could have cut heat-related mortality – which disproportionately affects older people and those living with disabilities – by up to 75%.

The past few weeks have been a taster of the effects of extreme heat (and humidity) in the UK. Encouraging home decarbonisation is one of the many ways that policymakers can help prevent the worst-case warming scenarios in overcoming decades.

At the same time, technologies such as A2A heat pumps can be both a preventive and adaptive measure: a lower carbon heating system that also helps people cope during the summer. While the UK currently lags behind other countries when it comes to AC uptake, survey data implies that the tide is starting to turn.

Dovetailing this change in consumer preferences into the country’s wider home decarbonisation efforts, by highlighting the dual benefit of A2A heat pumps and encouraging their use, could help tackle the issue of a changing climate from two sides at once.

In particular, the UK government should consider expanding permitted development for two outdoor units to other (non-detached) property types. Similarly, the Leasehold and Freehold Reform Act 2024 provides an opportunity for policymakers to reduce the challenges associated with strict leaseholds.

With more hot days and sticky nights on the horizon this summer and beyond, policymakers and households would do well to keep thinking about home heating – as strange as that sounds.