With the UK bracing for temperatures as high as 40°C this week, experts have issued guidance on the optimal times to open and close windows to keep homes cool. The Met Office has issued a rare red alert for Wednesday (June 24) and Thursday for certain areas, indicating hazardous weather with a significant risk to life.
When to Open and Close Windows
According to specialists, the decision to open or close windows depends on the relative temperatures indoors and outdoors. The experts at SCI Windows state: "Open the windows if house temperature is greater than outside temperature. Otherwise keep them closed to keep the cool air inside, as long as possible." They recommend keeping windows open at night when feasible and first thing in the morning before temperatures climb again.
Alan Reid, windows specialist at Art Windows and Doors, advises households to start opening windows at 8pm when outdoor temperatures begin to fall. John Small, owner of Ty Eco, suggests closing windows around 9am when temperatures start rising again, according to the Border Counties Advertiser.
Security Considerations
Leaving windows open overnight raises security concerns. Homeowners are advised to check if their windows have a night vent lock or 'night latch'. Many modern UK double-glazing systems allow the window to be secured while slightly ajar (about an inch). While less effective than a fully open window, it still permits essential night-time thermal exchange safely.
Expert Advice on Managing Heat
Dr Ben Roberts, an expert in building performance and indoor environments at Loughborough University, explains: "With overheating, it's a simple heat balance problem. We have too much heat going in - and not enough heat going out." He notes that the sun's heat comes through windows, hot air infiltrates from outside, and everyday activities like cooking, watching TV, or running appliances generate heat inside the home.
Dr Roberts advises: "Many people open their windows during the heat of the day, thinking it helps - but it actually does the opposite. During the day, your home can be a cool battery. The last thing you want to do is bring in hot air." He recommends keeping windows closed during the day, with reflective blinds or light-coloured curtains drawn on the sunny side of the house. Then, when it cools down in the evening, that's the time to open windows and let cooler air in.
