How to keep your house cool without aircon

UK homes are built to hold heat in, which is wonderful in January and miserable in a heatwave. Here is what genuinely helps, what is marginal, and what to do when none of it is enough.

Why UK houses get so hot

British housing is optimised for winter: insulation slows heat moving through walls in either direction, brick and block soak up the day's heat and release it into your evening, and modern builds are deliberately airtight. Loft conversions and top-floor flats sit directly under a roof that has been baking all day. None of that is a design fault - it is just a stock of housing that rarely had to think about cooling. It means the battle is won or lost on timing: keep heat out during the day, dump it overnight.

Shut the heat out by day

Most of a room's heat gain on a sunny day comes straight through the glass. Close curtains or blinds on sun-facing windows before the sun reaches them - east side in the morning, south and west from midday - rather than once the room is already warm. Light-coloured curtains and blinds reflect better than dark ones, and anything you can do outside the glass (awnings, external shutters, even a parasol leaned over a patio door) works better still, because it stops the heat before it enters. Keep windows shut while the air outside is hotter than the air inside; an open window at 3pm in a heatwave is a radiator.

Night purge: flush the heat out after dark

This is the most effective free measure in most UK homes. Once the outside air drops below your indoor temperature - typically late evening through early morning - open windows on opposite sides of the house so air can flow through, and open internal doors to connect them. If you have two storeys, opening upstairs and downstairs windows together lets warm air vent high while cooler air is drawn in low. Leave it running as long as security and comfort allow, then shut everything down again before the morning sun gets to work. A fan in a window blowing inwards (or outwards from the hottest room) speeds the exchange up considerably.

Stop making heat indoors

Everything that uses electricity ends up as heat in your rooms, but the offenders are not equal, so spend your effort where it counts:

• The oven is the big one. An hour's roasting heats the kitchen for the rest of the evening. Cook cold meals, use the microwave, or cook outside.
• Tumble dryers and dishwashers dump heat and moisture; skip them or run them late at night.
• TVs, consoles and desktop PCs add a modest but real amount to a small room over hours of use.
• Phone chargers and LED lights are negligible - do not waste your attention on them.

Reflective window film and foil

Reflective film stuck to sun-facing glazing bounces a worthwhile share of solar heat back out before it enters, and it works while you do nothing. It is one of the better cheap upgrades for a south- or west-facing room that overheats every summer. Two honest caveats: it also cuts winter solar gain and a little daylight all year round (removable or seasonal film avoids this), and taping kitchen foil to the glass does much the same job in an emergency while looking dreadful. Neither will rescue a room on its own; they shave the peak.

The tricks that barely work

An honest ranking, because heatwave folklore is persistent:

Fans still matter - across your skin, not at the walls. See portable aircon vs a fan for when moving air is genuinely enough and when it stops helping.

When passive measures are not enough

Everything above shaves degrees off the peak and buys you cooler evenings, and in a short hot spell that is often all you need. But in a proper multi-day heatwave the maths turns against you: the nights stop cooling down, the house's fabric is charged with heat, and a well-insulated bedroom can sit stubbornly in the high 20s at midnight. At that point the only appliance that actively removes heat from a room is a refrigerant portable air conditioner. Our size guide covers which BTU rating fits your room and our running costs guide covers what it costs per hour and per night to run.

The hard part is not choosing one - it is buying one, because everyone else reaches this conclusion in the same week and aircon sells out everywhere. That is the problem our live aircon stock tracker exists to solve: we check 17 UK retailers every 2 to 5 minutes and list what is genuinely in stock, including Argos and Screwfix click and collect at stores near you - often available when home delivery shows nothing. Free instant restock alerts on Telegram via @AirconWatchUK.

Keeping cool FAQs

Should I keep windows open or closed in a heatwave?

Closed, with blinds or curtains drawn, whenever the air outside is hotter than the air inside, which usually means most of the day. Once the evening air turns cooler than your rooms, open windows on opposite sides of the home so cooler air can flush the heat out overnight.

Does hanging a wet sheet in front of a fan cool a room?

Only slightly, and mainly in dry air. Evaporating water absorbs a little heat but raises humidity, and UK heatwaves are often muggy already, so the room can end up feeling clammier rather than cooler. Treat it as a short-lived comfort trick, not a way to lower room temperature.

What actually lowers a room's temperature?

Three things: stopping heat getting in with shading and daytime closed windows, flushing heat out when the outside air is cooler, and removing heat mechanically. Only a refrigerant air conditioner actively pumps heat out of a room, which is why passive tricks and fans stop being enough in a serious heatwave.