The UK is bracing for its third heatwave of the year, with the Met Office warning that a return to heatwave conditions is "increasingly likely" and temperatures could soar above 25°C in parts of Wales, reaching as high as 30°C by the weekend. As many people seek ways to stay cool indoors, a common question arises: should windows be kept open or closed during a heatwave?
Seven Experts, One Verdict
Seven specialists from various fields—including interior design, heating, health, and security—were consulted, and while their advice varied slightly, they all reached the same fundamental conclusion: windows should not remain open continuously during the hottest parts of the day.
Johanna Constantinou, interior trends specialist at Tapi Carpets and Floors, stated: "During a heatwave, one of the biggest mistakes people make is having all the windows open during the hottest part of the day. In most homes, it's actually far more effective to keep windows, curtains and blinds closed from late morning through to early evening to stop warm air and direct sunlight building up indoors. Then, once temperatures drop in the evening, open windows strategically on opposite sides of the home to create cross ventilation and let cooler air circulate naturally."
Why Keep Windows Closed During the Day?
Martyn Bridges, Director of External Affairs at Worcester Bosch, reinforced this guidance: "During a heatwave, people should generally keep windows closed during the hottest parts of the day, particularly in rooms exposed to direct sunlight. Blinds or curtains should also be kept closed during the day to help block out direct sunlight and prevent rooms from becoming too hot. This helps reduce solar gain, where the sun warms the home and causes indoor temperatures to rise."
The principle is simple: during daylight hours, outdoor air is warmer than indoor air, so opening windows lets heat in. By closing windows, curtains, and blinds, you create a barrier that traps cooler air inside and reflects sunlight.
Night-Time Cooling Strategy
When evening arrives and outdoor temperatures drop, the experts recommend opening windows to let in cooler air. Dr Katie Tryon from Vitality Health explained: "There are several things you can do to help yourself stay cool at night. Firstly, it's important to keep your bedroom cool. Drawing curtains and blinds during the day and keeping windows closed if in direct sunlight to stop hot air getting in can help. When night comes and the air gets cooler, leaving the window ajar to let a cool breeze in can also make it easier to sleep."
Dr Punam Krishnan, working with Stannah, emphasised that physical preparation is equally important: "While methods such as opening windows and using electric fans to cool your room's temperature are widely recognised, it's important to also focus on cooling down your body, as well as your surroundings, to maintain a high sleep quality during the summer months."
Creating a Cross-Breeze
Victoria Robinson, a product expert at Hillarys, advised opening windows on opposite sides of the home to generate a cross-breeze. She said: "Once temperatures start to drop in the evening, that's the best time to open windows and allow cooler air to circulate through your home. Creating a cross-breeze by opening windows on opposite sides of the house can help cool rooms down more quickly."
Professor Chris Sansom, a specialist in renewable energy storage at the University of Derby, echoed this: "Give thought to the windows in your house that you're opening. For example, opening windows on the opposite sides of your home can create a much-needed, cooling cross-breeze. For even better results, try opening your windows at night-time and closing them during the day to trap cooler air inside and keep it circulating. During daylight hours, open windows on the shaded side of your home to reduce the amount of heat and sunlight entering your home."
Security Considerations
There is also a security angle. Craig Andres from The Perspicacity Life warned: "Temperatures are set to soar over the bank holiday weekend and while it's tempting for households to leave windows open, it's important not to overlook home security. Simple security mistakes such as leaving keys in locks or within reach of open windows, leaving doors unlocked, or windows ajar create easy opportunities for burglars, and more than a quarter of summer burglaries are linked to these oversights."
Conclusion
The unanimous advice from all seven experts is clear: keep windows closed during the hottest part of the day to block out warm air and direct sunlight. In the evening, once temperatures drop, open windows on opposite sides of the home to create cross-ventilation and let cooler air circulate. This strategy not only helps maintain a comfortable indoor temperature but also improves sleep quality and home security.
