As summer temperatures soar, many homes become uncomfortably warm, particularly overnight. While the natural inclination is to open windows for fresh air when heat intensifies, a key question arises: is it more effective to keep them closed?
Should you keep windows open or closed during a heatwave?
According to NHS advice, curtains should be kept shut to keep sun-facing rooms as shaded as possible. The health service also advises drinking plenty of fluid, avoiding excess alcohol, staying out of the sun between 11am and 3pm, and refraining from exercise during the hottest part of the day.
Professor Amin Al-Habaibeh, an expert in heat transfer in buildings at Nottingham Trent University, explains: “It is all about heat transfer. We need to reduce heat gain to inside the building in hot weather. Heat gain comes mainly from two sources: solar radiation and hot air. Also we need to avoid the greenhouse effect as this would increase the temperature inside the house.”
He adds: “If you have a conservatory, it is important to keep windows open during the day and ideally isolate it from the rest of the house to reduce thermal gain due to the greenhouse effect. It is important to keep the curtains closed during the day to reduce solar gain inside the house.”
On whether to keep windows open, Al-Habaibeh says it depends on the type of house and outside temperatures. “In short, open windows when the temperature inside the house becomes greater than the external temperature, otherwise keep the windows closed,” he explains.
Dr Lindsay Browning, psychologist and sleep expert at bed retailer And So To Bed, agrees. “Generally, when it is really hot outside it is a good idea to keep windows closed during the daytime, as you don’t want the hot external air to come into the house warming it up. However, after the sun goes down, the outside air will start to cool down. At this point, it is a great idea to open the windows to let in a breeze of cool external air into the bedroom, helping cool the room and providing needed air circulation.”
She also recommends keeping the room dark during the day to prevent the sun from heating it up.
A spokesperson for NHS Property Services recommends “closing blinds and curtains in rooms that face the sun, opening windows on the side of the building that is in the shade, but closing windows that are in direct sunlight”. They also advise keeping windows closed if you have air conditioning so that cooler air can circulate.
