Two heatwaves, one study, one very sobering number. On 13 July 2026, researchers from Imperial College London, the UK Met Office and the London School of Hygiene & Tropical Medicine published a rapid mortality analysis covering England and Wales for May and June. Sky News and other outlets picked it up with the toll already past 2,000; the researchers' own central estimate is higher still.
The study's own framing is worth sitting with: climate change is estimated to have added 3–4°C on top of what these heatwaves would otherwise have reached, and that added heat alone accounts for more than 40% of the deaths recorded. This isn't a freak event any more — it's the shape of a British summer now, and as of this week the country is in its third heatwave of the year, with amber heat-health alerts covering most of England and forecasts running hot into 16–17 July.
We've written before about the rising number of days above 25°C in southern England. This is the sharper version of that argument: those days aren't just uncomfortable, they are now measurably lethal for the most vulnerable people in the country — the elderly, people with heart and respiratory conditions, and anyone in a home that can't shed heat overnight. Which makes the question of how you actually cool a British home a lot less academic than it was five years ago.
The heat pump you already have probably can't do this
Here's the awkward bit for the roughly one million UK households now on an air-to-water heat pump, most fitted under the Boiler Upgrade Scheme for exactly the right reasons: most of them are not built to cool your home properly, even the ones marketed as reversible.
The physics is the same reason your bathroom mirror steams up. Run cold water through underfloor pipes or radiators and, if the pipe surface drops below the room's dew point, water condenses straight out of the air onto the floor or radiator. On a humid July day that dew point might sit around 16–18°C, so a "cooling" air-to-water system has to keep its flow temperature a safe 2–3°C above that — which caps how cold the floor is ever allowed to get. Installers call the result "light cooling" or "dry cooling": it takes the edge off, typically 2–4°C below ambient, but it is nowhere close to what a proper air-conditioner does, and on the genuinely hot days — the 30°C-plus days when it actually matters — it can't keep up at all. Push flow temperatures lower to compensate and you risk exactly the condensation, damp patches and eventual mould the safety margin exists to prevent.
Why "our heat pump does cooling too" is often marketing
A reversible air-to-water heat pump absolutely can run backwards and chill the water in your emitters. The catch is what it's chilling: radiators and underfloor loops were never designed to run cold, so the system has to throttle itself well short of real air-conditioning to avoid condensation. It is a genuine feature — just not the feature most buyers think they're getting when a brochure says "heating and cooling in one unit."
Air-to-air does the job properly — because it's the same thing as air-con
The other branch of the heat pump family, air-to-air, doesn't have this problem, because it isn't trying to chill water at all. It moves heat directly between outside air and indoor air through a wall-mounted unit — it is, mechanically, exactly what people mean by air conditioning, just built to run in reverse for winter heating too. There's no pipework to keep above dew point and no floor to protect: the indoor unit simply dehumidifies and cools the room air directly, the way a hotel air-con unit does. We've covered the case for this in detail, including running air-to-air alongside a Sunamp instead of a wet system entirely, and the basic heat pump economics for 2026 if you're weighing this up from scratch.
The industry has noticed — hence the new joint units
The neatest fix for the "grant-funded air-to-water heats but can't really cool" problem turns out not to be picking a side, but combining both in one outdoor unit. We looked at this properly in our Daikin X Series vs Samsung EHS Quint piece: both brands have now announced heat pumps that run air-to-air cooling, air-to-water heating and hot water from a single compressor. Samsung's EHS Quint is orderable now and has a genuinely clever trick — heat recovery, where the heat pulled out of a room you're cooling gets diverted into your hot-water cylinder instead of being dumped outside. You needed that hot water anyway; here it arrives as a free by-product of cooling you also wanted. Daikin's X Series, landing in September, takes the other approach: one shared compressor allocating capacity across air-to-air, hydronic heating and hot water as demand shifts, rather than two machines that never talk to each other.
Neither is a slam-dunk yet — no independent UK field data exists for either, and Daikin hasn't published a COP. But the direction is unmistakable: the "air-to-water or air-to-air" fork was always artificial, driven by legacy product lines rather than what a home in a country with 2,700 heat deaths in one summer actually needs from its heating system.
What it looked like at Rose Cottage
Numbers are easier to trust with a real meter behind them. Rose Cottage runs three air-to-air units as zonal cooling, and Homey — the automation hub that's the source of truth for everything else on this roof — logged exactly how much electricity that took across this heatwave-heavy July.
Figure 1 — Cooling electricity by room, July 2026 to date. Garden Room and Master Bedroom carry the load because they get the most sun; combined, the house's air-con used 196.4 kWh this month keeping every room comfortable through two amber heat-health alerts. Source: Homey Insights, Decarbonarma home monitoring.
All of it came off solar that would otherwise have been thrown away
The house has a 6 kWp array behind a G100 export limiter capped at 6 kW. On the bright, still days that also happen to be the hottest ones, the panels can produce well beyond that cap — and without a load to soak up the difference, the inverter simply clips the surplus and it's generated for nothing. Running the air-con through the hottest hours of the day does exactly the job the EV charger does on other days: it turns power that would have been curtailed to zero into cooling that keeps the house at 21°C. On the worst days of this heatwave, cooling the whole house cost precisely £0 in marginal terms — it was surplus the grid was never going to take anyway.
The bottom line
Sky News rounding the toll to "over 2,000" undersells it — the researchers' own number is over 2,700, in two heatwaves, in one summer, and there's likely a third contributing before the year is out. That is a public health number now, not a comfort number, and it changes what "do you need air conditioning" actually means. The honest technical answer is that most UK heat pumps — the air-to-water ones funded by the grant scheme — were never built to solve this problem, and the condensation limits on their cooling mode are physics, not a firmware gap the next update will fix. Air-to-air does the job properly, the new joint A2W+A2A units from Samsung and Daikin are where the industry is heading next, and at Rose Cottage the whole exercise cost nothing extra, because the sun that nearly killed 2,700 people this summer is the same sun that kept this particular house at 21°C.