How do I keep my house cool in a heatwave?

Cooling a house without air conditioning is about timing. Once the outside air is hotter than the inside, opening windows makes it worse. The house needs to be sealed during the day and flushed with cool air at night.

Safety

What you'll need

• Curtains or blinds (optional)
• A fan (optional)
• Thermometer (optional)

Step by step

1. Close windows and curtains before it gets hot.Early morning, before the outside temperature exceeds the inside. Once you have missed that moment, opening windows brings heat in.
2. Block direct sunlight, ideally from outside.External shading is far more effective than internal, because it stops the heat before it enters the glass. Awnings, shutters or even a temporary reflective cover.
3. Open everything at night once it is cooler outside.Windows on opposite sides for cross-ventilation. This is when the house sheds the heat it accumulated.
4. Use fans to move air across you, not to cool the room.A fan does not lower the temperature; it helps sweat evaporate. Pointing it at people is effective, pointing it at an empty room is not.
5. Turn off anything producing heat.Ovens, tumble dryers, unnecessary lights and electronics. Cook outside or use a microwave or air fryer rather than the oven.
6. Close doors to unused rooms.It concentrates cooling effort in the rooms you use. Ground floor and north-facing rooms stay coolest.
7. Use a damp towel or a bowl of ice with a fan.Air passing over ice or a wet cloth is cooled by evaporation. It is modest but genuinely effective in a small space.
8. Check on anyone vulnerable.Older neighbours and relatives, anyone with a health condition. Heat is a genuine health risk and people underestimate it.

Tips

• The loft gets extremely hot and radiates into upstairs rooms. Good loft insulation keeps heat out in summer as well as in during winter.
• A portable air conditioner needs its exhaust hose vented properly outside. Venting it into the room defeats the purpose entirely.
• Sleep downstairs if upstairs is unbearable. Heat rises and a ground floor room is often several degrees cooler.

Common mistakes

• Opening windows during the hottest part of the day — It brings hot air in. Once outside is hotter than inside, the house should be sealed.
• Leaving a fan running in an empty room — Fans do not cool air; they help sweat evaporate from skin. Running one with nobody there adds heat from the motor.
• Using the oven during a heatwave — It adds a substantial amount of heat to the house that then has to be shed overnight.

Questions people ask