Heat and health in Europe: how cool a home needs to be, and for whom
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Search for the temperature a home should be kept at during a heatwave and you will be told, confidently and in several places, that the World Health Organization recommends 26 °C. It does not. What the WHO Housing and Health Guidelines actually did, after reviewing the evidence on indoor heat, was decline to set a universal maximum — and understanding why is more useful than the invented number, because it points at the thing that does decide the answer.
The stakes are not theoretical. Peer-reviewed estimates published in Nature Medicine put heat-related mortality in Europe at roughly 61,700 deaths in the summer of 2022 and around 47,700 in 2023, concentrated in exactly the countries and the age groups you would expect. Cooling in Europe stopped being a comfort question somewhere in that decade, and our guide to Europe heatwaves since 2003 traces how the record got there.
Why there is no single number
The WHO review found only a handful of eligible studies linking indoor temperature to health outcomes, with low to very low certainty, and no direct evidence for any particular threshold. What it issued instead was a conditional recommendation that, in populations exposed to high ambient temperatures, strategies to protect people from excess indoor heat should be developed and implemented — with targets set regionally, because acclimatisation moves the goalposts. The minimal-risk temperatures cited in that work span a wide band: in the region of 23 °C in northern continental cities, and close to 29 °C in Mediterranean ones.
That spread is the practical lesson. A living room at 28 °C in Seville is an ordinary August afternoon for a resident who has lived through forty of them. The same 28 °C in a Dutch or Danish flat, in a population that has never adapted to it, arrives with measurably more risk. Anyone quoting one European indoor limit is quoting something that does not exist.
What the night actually decides
The variable that separates an uncomfortable heatwave from a deadly one is not the afternoon peak but the run of nights. Body core temperature falls during sleep; it cannot fall in a bedroom that has not cooled, and after two or three consecutive hot nights the physiological debt accumulates in precisely the people least able to carry it. Meteorologists call a night that stays at or above 20 °C a tropical night, and the count of them is rising faster in European cities than the count of hot days.
This is why, if a household is going to cool one room, it should be the bedroom, and why the sizing and the noise of that machine matter more than its brochure efficiency. The working rules are in our guide to bedroom air conditioning.
Who is genuinely at risk, and what changes for them
| Group | Why the risk is higher | What to change first |
|---|---|---|
| People over 75, especially living alone | Reduced thirst sensation and sweating response; isolation means nobody notices the decline | One cool room, a daily phone call, and registration on the municipal vulnerable-persons list where the country runs one |
| Infants and young children | High surface-to-mass ratio, no control over their own environment | Bedroom below roughly 24 °C at night, no air stream on the cot, fluids on demand |
| Chronic heart, lung or kidney disease | Heat raises cardiac demand while fluid balance is already managed tightly | A refuge room that stays moderate all day rather than intermittent cooling |
| People on certain long-term medications | Diuretics, anticholinergics and several psychotropics alter fluid balance or thermoregulation | Ask the pharmacist before a heatwave, not during one — this is a medical question, not a housing one |
| Outdoor and hot-workplace workers | Exertion adds internal heat on top of ambient heat | Recovery at home matters as much as the shift itself; see our guide to workplace temperature rules in Europe |
| Anyone in a top-floor or single-aspect flat | The building, not the person, is the hazard: roof gain and no cross-ventilation | External shading and night flushing first, then a correctly sized machine — see cooling a loft or attic room |
The cool-room strategy, and what it costs
Cooling an entire European dwelling to a fixed temperature is expensive, usually needs consent for several outdoor units, and is rarely what protects anyone. Cooling one room properly does. Pick the bedroom or the room where the person at risk spends the day, seal it, shade its glass, size the machine for that room alone and run it as a refuge — moderate setpoint, continuous rather than in bursts.
The bill for that is smaller than most people fear. A 2.5 kW split holding a shaded, closed bedroom typically settles at part load and draws in the order of 0.2 to 0.6 kWh per hour once the room is down; over an eight-hour night that is roughly 2 to 5 kWh, which at European domestic tariffs of around 0.15 to 0.35 € per kWh works out at something like 0.30 € to 1.75 € a night. Those are indicative orders of magnitude, not a quotation — the method for your own tariff and machine is in our guide to AC running costs in Europe, and the sizing method in our guide to AC sizing in kW.
Before any of that, the free half of the job is worth doing, because it decides how hard the machine has to work and it keeps working during a power cut: external shading on the glass that receives sun, closing the house during the day, flushing it at night. Our guide to cooling a home without air conditioning sets out the order.
Cooling in a way that does not create its own problems
- Do not chase extremes. A setpoint of 19 °C in a room of frail or elderly people is not protective; it produces a large shock on entering and leaving and costs several times what a moderate setting does. Our guide to the best AC temperature setting gives the cost of each degree.
- Keep the air off the person. Aim the louvres along the ceiling, never at a bed, a cot or an armchair. Continuous cold air on the neck of someone immobile for hours is the origin of most of the "air conditioning made me ill" stories.
- Watch humidity, not just temperature. A room at 27 °C and 45 % relative humidity is tolerable; the same room at 70 % is not, and the machine handles both if it is not grossly oversized.
- Keep the machine clean. Filters and a free-draining condensate tray are the difference between cooler air and a biofilm blowing at a vulnerable person all night.
- Have a plan that survives the machine. Grids are most stressed exactly when heat peaks. Water, cool showers, a shaded low-level room and a neighbour who checks daily are the part of the plan that does not need electricity.
The intervention with the best evidence behind it is social
Across the analyses of 2003, 2022 and 2023, the strongest single predictor of a heat death in Europe is not the absence of an air conditioner: it is being old, alone and unvisited. Every national heat-health action plan built since 2003 is organised around that finding, which is why municipalities keep vulnerable-persons registers, why alert levels trigger phone calls rather than equipment grants, and why a daily call to a parent in a hot flat does more than any purchase on this site could. Buy the machine if the building needs it — and make the call regardless.
Frequently asked questions
Does the WHO recommend 26 °C indoors?
No. The WHO Housing and Health Guidelines deliberately set no maximum indoor temperature, because the evidence was too thin and because the temperature that carries minimal risk differs by region and by how acclimatised a population is — roughly 23 °C in northern continental cities against nearly 29 °C around the Mediterranean. The 26 °C figure circulating online generally comes from national energy-saving rules for public buildings, which is a different subject entirely.
Is air conditioning bad for your health?
Not in itself. The harm attributed to it comes from three avoidable habits: excessive temperature differences, a cold air stream played directly on a stationary person, and a machine whose filters and drain have never been cleaned. Corrected, cooling is a protective measure for people at risk — it is what hospitals and care homes across southern Europe rely on every summer.
Is a fan enough during a heatwave?
Up to a point, and that point is real. Moving air helps while sweat can still evaporate, but several national health authorities warn that above roughly 35 °C blowing hot air over a frail or elderly person accelerates dehydration rather than cooling them. At that stage cool showers, fluids, damp cloths and a genuinely cooler room matter more than air movement.
Which room should I cool if I can only cool one?
The bedroom of the person most at risk, or the room where they spend the afternoon if the two differ. Nights are what the body needs for recovery, so if the choice is between an unbearable afternoon and an unbearable night, cool the night. A small, well-sealed, well-shaded room is also the cheapest thing a small machine can hold.
How do I know a heatwave is coming?
Every European country now runs a heat-health warning system through its national meteorological service, with colour-coded levels that trigger public-health measures. Signing an elderly relative up for the local register and knowing the alert level for their region two days ahead is the whole of the preparation most households need.
Sources
Read next
- The room under the roof: cooling a loft conversion in Europe
- Air conditioning that has stopped cooling: the European diagnosis order
- Europe’s heatwaves: the record of a continent warming fastest
- Too hot to work? Workplace temperature rules across Europe
- How far can the outdoor unit sit from the indoor unit?