Portable aircon vs a fan in a UK heatwave
One costs pennies a day, the other actually lowers the temperature. The honest answer to "do I really need aircon?" depends on how hot your rooms get - here is how to decide without wasting money either way.
The physics, in one paragraph
A fan does not cool a room at all. It cools you, by moving air across your skin so sweat evaporates faster - the same reason a breeze feels good. The room's temperature stays the same, or rises fractionally, because the fan's motor adds a little heat. A portable air conditioner is a different machine entirely: a heat pump that pulls heat out of the room air and dumps it outside through an exhaust hose, while also wringing moisture out of the air. It is the only common household appliance that makes a room genuinely cooler and drier than the air outside.
When a fan is genuinely enough
For most British summer weather, a decent fan is honestly all you need. It earns its keep when:
- Room temperatures are warm rather than extreme - up to roughly 30°C, moving air still feels properly cooling.
- You mainly need help sleeping and the bedroom cools down at night anyway.
- The air is reasonably dry, so sweat evaporates and the breeze does its job.
- You can pair it with open windows after dark to pull cooler night air through.
A fan is cheap to buy, silent enough on low, and costs pennies to run all night. If your home only gets uncomfortable a handful of days a year, stop reading here and buy a good fan.
When a fan stops helping
Fans fail in exactly the conditions that make UK heatwaves dangerous. UK hot weather guidance warns that once air temperature climbs above about 35°C, a fan is mainly blowing hot air over you, and can add to dehydration and heat stress rather than relieve it. Humid heat is the other failure mode: when the air is muggy, sweat stops evaporating efficiently, so the breeze loses most of its cooling effect - which is why a fan can feel useless on a sticky night at 28°C. And if your bedroom holds its heat into the small hours, as many well-insulated UK homes do, a fan just stirs that heat around. An air conditioner keeps working in all three cases, because it removes heat and moisture rather than moving them about. For anyone elderly, pregnant, very young or managing a health condition, that difference matters most.
The evaporative cooler trap
Between fans and real aircon sits the "air cooler": a fan blowing over a tank of water. Evaporating water does absorb some heat, so these work tolerably in hot, dry climates. UK heatwaves are often humid, and in humid air an evaporative cooler barely lowers the temperature while pumping extra moisture into the room - leaving it feeling stickier than before. They are frequently listed alongside real air conditioners at similar prices, which is how people end up disappointed. The tell: a real portable air conditioner has a compressor, a BTU rating and an exhaust hose. An air cooler has none of those - and AirconWatch deliberately does not track them.
What each costs to run
A typical fan draws tens of watts, so even running all night it costs pennies a day. A portable air conditioner draws around a kilowatt, give or take, which works out at very roughly 20 to 40p per hour depending on the unit's size and your electricity tariff - and less in practice once the thermostat starts cycling rather than running flat out. Our running costs guide works through per-hour and per-night figures by unit size. The gap is real, but so is the difference in what you get: one appliance moves warm air around, the other removes it.
The honest verdict
| Situation | Buy |
|---|---|
| Warm spells, rooms below ~30°C, cool nights | A good fan |
| Muggy, sticky heat that ruins sleep | Portable aircon |
| Rooms that stay hot after dark (lofts, flats, south-facing) | Portable aircon |
| Extreme heat, or vulnerable people in the household | Portable aircon |
| Hot dry climate abroad | Evaporative cooler - but not in the UK |
The two also work well together: an air conditioner to bring the room down, a fan to spread the cooled air and let you set the AC a degree or two higher.
If you land on aircon, get the size right before you buy - an undersized unit disappoints and an oversized one leaves the room clammy. Our portable air conditioner size guide matches BTU to UK room sizes in two minutes.
The catch: buying one in a heatwave
The moment fans stop coping is the moment everyone else reaches the same conclusion, and retailer stock evaporates - why aircon sells out everywhere explains the mechanics. Rather than trawling sold-out pages, use our live aircon stock tracker: we check 17 UK retailers every 2 to 5 minutes, including Currys and Argos, with Argos and Screwfix click and collect mapped to stores near you. Free instant restock alerts via @AirconWatchUK on Telegram. And while you wait for stock, see how to keep your house cool without aircon.
See which portable air conditioners are in stock now →AirconWatch checks 17 UK retailers every 2 to 5 minutes - real refrigerant units only, never fans or coolers - with Argos & Screwfix click & collect near you and free Telegram alerts.
Aircon vs fan FAQs
Do fans work in a heatwave?
Up to a point. A fan cools you rather than the room, by moving air across your skin so sweat evaporates faster, and in air up to around 30°C that usually feels genuinely good. In extreme heat, above about 35°C, UK hot weather guidance warns that a fan is mainly blowing hot air at you and can make heat stress worse rather than better.
Can a fan make a room hotter?
Slightly, yes. A fan's motor adds a small amount of heat, so a fan running in a closed room nudges the temperature up rather than down. All of the cooling you feel comes from moving air helping sweat evaporate, which is why a fan does nothing to the room itself.
Are evaporative air coolers worth buying in the UK?
Usually not. They cool by evaporating water into the air, which works well in hot, dry climates but poorly in humid UK heatwaves, and the moisture they add can leave a room feeling stickier. If you need the room itself cooler, you need a refrigerant unit with an exhaust hose.