The UK is forecast to be hit by temperatures as high as 40C this week, and experts have shared the best times to open and close your windows to keep your house cool15:40, 22 Jun 2026With Britain sweltering in another scorching heatwave, discussion has once more shifted to whether folk should keep their windows open or shut to combat the heat.‌Weather forecasters predict that temperatures across parts of the nation could soar as high as 40C this week, which would shatter the all-time June record that has stood for half a century.‌The Met Office issued a rare red alert warning for Wednesday (June 24) and Thursday for certain areas of the country, signifying that hazardous weather is expected with a significant likelihood of risk to life.‌With this in mind, people are frantically attempting to stay cool, but should you open your windows or keep them shut?According to specialists, that very much depends on how the outside temperature compares to the conditions inside your home, reports the Express.The experts at SCI Windows say: "There is lots of advice available on the internet, but the general rule is: 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 suggest keeping the windows open at night when feasible and also first thing in the morning, before the temperature begins to climb again.They added: "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."‌Alan Reid, windows specialist at Art Windows and Doors, informed the Manchester Evening News that households should begin opening their windows at 8pm when outdoor temperatures begin to fall.UK housebuilder and Ty Eco owner John Small believes windows ought to be closed around 9am in the morning when temperatures begin climbing again, according to Border Counties Advertiser.Leaving windows open overnight brings some clear security concerns. Homeowners are recommended to check whether your windows feature a night vent lock (or 'night latch').‌Numerous contemporary UK double-glazing systems enable you to secure the window while it remains slightly ajar by roughly an inch. It's not as effective as a fully-open window, but it will still permit that essential night-time thermal exchange to occur safely while you sleep.According to Dr Ben Roberts, an expert in building performance and indoor environments at Loughborough University, who explained how vital it is to manage our properties during warm weather.‌He stated: "With overheating, it's a simple heat balance problem. We have too much heat going in - and not enough heat going out."The sun's heat comes through windows, hot air infiltrates from outside, and even everyday activities like cooking, watching TV or running appliances all generate heat inside the home."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.Article continues below"Instead, windows should stay 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 your windows and let the cooler air in."