As the UK braces for temperatures soaring to 40C this week, experts have issued clear guidance on when to open and close windows to stay cool. The Met Office has issued a rare red alert for Wednesday and Thursday, warning of dangerous weather with a high likelihood of risk to life.
When to Open Windows
According to Alan Reid, a window expert at Art Windows and Doors, people should start opening their windows at 8pm when the outside temperature begins to drop. This allows cooler night air to circulate and reduce indoor heat. Experts at SCI Windows recommend keeping windows open at night and first thing in the morning before temperatures rise again.
John Small, owner of Ty Eco and a UK housebuilder, advises shutting windows around 9am when temperatures start climbing again, as reported by the Border Counties Advertiser. During the day, windows should remain closed to keep cool air trapped inside.
Why Closing Windows During the Day Helps
Dr Ben Roberts, a specialist in building performance at Loughborough University, explained: "During the day, your home can be a cool battery. The last thing you want to do is bring in hot air." He emphasised that opening windows in the heat of the day actually brings in hot air, making the home warmer. Instead, windows should stay closed with reflective blinds or light-coloured curtains drawn on sunny sides.
Experts at SCI Windows add: "Letting air circulate around the house is easily the best method of keeping inside temperatures down. By doing this, you should be able to create a flow of air, then cold air can be pushed through each room."
Security Considerations at Night
Keeping windows open at night raises security concerns. Experts recommend using a night vent lock or 'night latch' if available. Many modern UK double-glazing windows allow locking while cracked open by about an inch, enabling safe thermal exchange without compromising security.
The heatwave is expected to break the all-time June record of 40C, which has stood for 50 years. With such extreme temperatures, managing indoor heat is critical for health and safety.
