The short answer
Keep the sun off your windows during the day, open up when the air outside is cooler than inside, usually from late evening to early morning, and cut the heat produced indoors. Fans make you feel cooler, though they don't cool the room.
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Many UK homes are built mainly to hold on to heat, so in a hot spell they can warm up a little more each day and struggle to cool down at night. The measures below work together: shading stops heat getting in, ventilation lets it out when the weather allows, and cutting indoor heat stops you adding to it.
Keep the sun out
On a sunny day, sunshine through the windows is often the biggest source of heat in a room. Once it has passed through the glass the heat is inside, so the aim is to stop it before it gets that far.
| Shading | How well it keeps heat out | Things to know |
|---|---|---|
| Shutters, awnings and outside blinds | Best | Stop sunshine before it reaches the glass |
| Trees, climbers and pergolas | Good, once established | Deciduous plants let winter sun through |
| Light or reflective-backed blinds and curtains | Moderate | Close them before the sun arrives |
| Dark blinds and curtains | Least | Absorb heat and warm the room |
| Solar control window film | Varies | Cuts some light too; check it suits your glazing |
Follow the sun round the house. East-facing windows need shading in the morning, south-facing ones around the middle of the day, and west-facing ones from the afternoon into the evening. North-facing rooms usually stay coolest, so they're the ones to use in the hottest part of the day. Why some rooms overheat explains why direction matters so much.
Ventilate at the right times
Open windows when it's cooler outside than inside, and close them when it's warmer. On a hot day that usually looks like this:
| Time | Windows | Blinds and curtains |
|---|---|---|
| Early morning | Open while the air is cool | Open on shaded sides |
| Late morning to evening | Closed once it's warmer outside | Closed on sunny sides |
| Late evening and night | Open once it's cooler outside | Open, so air can flow |
A thermometer that shows both indoor and outdoor temperatures takes the guesswork out of it. A stuffy room on a hot afternoon is tempting to air, but opening up then lets hotter air in.
Air moves best with a way in and a way out:
- Cross-ventilation. Open windows on opposite sides of the house, with internal doors open between them while you're up. Fire services advise closing internal doors at night.
- Stack ventilation. Open a window high up, such as upstairs or a roof window, and another low down. Warm air leaves at the top and draws cooler air in at the bottom.
- Security. Only leave windows open where it's safe. Lockable window restrictors let you leave a window slightly open overnight, and fly screens keep insects out.
Cut the heat made indoors
Almost everything that uses energy indoors ends up as heat. On hot days:
- Switch off televisions, computers and games consoles you aren't using.
- Use a microwave, kettle or barbecue rather than the oven, or cook in the cooler part of the day. Put lids on pans and run the cooker hood.
- Dry washing outside where you can. Tumble dryers add heat, and drying washing indoors adds moisture, which makes warm air feel stickier.
- Replace halogen and old-style filament bulbs with LEDs, which give off far less heat.
- Check that heating timers, heated towel rails and electric underfloor heating aren't still switching on.
- Close the bathroom door and run the extractor fan while showering, so warm, moist air doesn't spread through the house.
Fans
A fan doesn't lower the temperature of a room. It moves air across your skin, which helps you feel cooler, and its motor adds a little heat, so switch it off when you leave the room.
Desk, pedestal and tower fans can move with you from room to room. Ceiling fans move air around a whole room, but need enough ceiling height and fitting by an electrician. At night, a fan facing out of an open window pushes warm air out while cooler air comes in through windows open elsewhere.
Evaporative coolers blow air through a wet pad. They add moisture as they cool, so they work best in dry air and do less on a humid day. Evaporative air coolers explains how they compare.
If the heat is affecting your health, or the health of someone you look after, follow the NHS's advice on hot weather.
Longer-term changes
If your home overheats every summer, some changes keep working year after year:
- Shutters, awnings or outside blinds on the sunniest windows.
- Trees or climbing plants for summer shade.
- Topping up loft insulation, which slows heat coming through the roof into top-floor rooms.
- Solar control glass when windows are due for replacement.
- Windows that can be left open securely at night.
On a listed building or in a conservation area, check with the local council before fixing anything to the outside. Bedrooms that stay hot at night need particular attention, and sleeping in hot weather covers them in more detail.
Related guides
- Why some rooms overheatA room overheats when heat gets in or builds up faster than it can escape. The usual causes are sunshine through large or west-facing windows, a roof directly above, heat from people and equipment, and too little ventilation.
- Sleeping in hot weatherBedrooms stay warm at night because the building gives back the heat it soaked up during the day. Keeping sun out by day, ventilating once it's cooler outside, and quiet cooling or a fan all make a warm night more comfortable.
- Doors, windows and blindsKeep doors and windows shut while the system runs, and close blinds or curtains on sunny windows in warm weather. In winter, let the sun in by day and close curtains at dusk.
- Evaporative air coolersAn evaporative air cooler blows air through a wet pad so that evaporating water cools it. It uses little electricity and needs no hose or installation, but it isn't air conditioning, adds humidity and does little on humid days.