As our homes become increasingly hot and stuffy, the temptation is to open a window – but counterintuitively, Dr Andrew Shea, Senior Lecturer in Building Physics in the Department of Architecture and Civil Engineering at University of Bath, claims this is wrong.
“If it’s cooler inside than outside, you should keep the windows closed,” he says, aptly The Guardian.
While it’s easy to imagine that opening the windows wide might bring in a nice cool breeze, you’ll most likely just be bringing warm air in, making your living space even more stuffy.
“If you have a shaded area at the back of the house, for example, you can open a window there – but generally. However, just hang on to that last bit of cool air inside,” he says.
Dr Ana Souto, senior lecturer at Nottingham Trent University’s school of architecture, design and environment, says her true expertise in keeping cool comes from being of Spanish descent.
“Close everything,” she advises. “You can open the windows late at night and early in the morning – until 9am or so – when it’s cool, but otherwise keep them closed. My home is like a cave, but it works.”
Amin Al-Habaibeh, professor of intelligent engineering systems at Nottingham Trent University, suggests some exceptions to the closed windows rule.
“Heat enters the house in two ways: solar radiation from the sun and warm air. We want to limit both by closing the windows and the curtains – but if it gets to a point where the temperature inside the house is equal to the temperature outside, then we should open the windows and keep the curtains drawn.”
The location of the windows can also have an impact.
“Sometimes, with south-facing windows, closing the window and drawing the curtains can create a greenhouse effect between the two – and this can be another source of heat,” says Professor Al-Habaibeh. “In this scenario, opening a window can help reduce heat dispersion from the south side.”
He also suggests that balcony windows should always be kept open during a heatwave – “otherwise a greenhouse effect is created – and the door between the balcony and the house should be kept closed”.
But other justifications for opening a window – like the idea that placing a towel or damp cloth in front of the airflow might help? Dr. Shea remains skeptical.
“It could work in principle, but I wouldn’t do it in these extreme weather conditions,” he says. “Evaporation of water takes some of the heat out of the air, but the degree of cooling would not be enough to make a difference. If your house has already reached unbearable temperatures, then it could be a last resort. But with all that, it’s better to keep the hot air out altogether.”
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