Medical News
Should you open your windows or close them? Can plants help, and should you get air conditioning? This is your guide to staying cool at home during a heatwave
Environment
25 July 2019
Most of our homes have not been designed with heatwaves in mindRudi Gobbo/getty
By Sam WongScorching hot summers were once rare in the UK, but thanks to global warming, they are more likely to occur. However, most buildings in this country have not been designed with sizzling heat in mind, and many of us struggle to keep our homes and offices cool when temperatures get above the mid-20s.
So what can we do to improve the situation? Some sources, including the National Health Service website, advise people to keep windows closed. That’s a big mistake, says Sue Roaf at Heriot-Watt University.
The main mechanism our bodies have for cooling down is sweating. This works much more effectively if air is moving over our skin. “You need ventilation to actually cool the body down,” says Roaf. That is why a hot room feels much more comfortable with a fan.
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The NHS website says: “Shut windows and pull down the shades when it’s hotter outside. You can open the windows for ventilation when it’s cooler.”
The NHS said their advice is based on the Heatwave Plan for England. But the advice in this document is more nuanced. It says: “Keep windows that are exposed to the sun closed during the day, and open windows at night when the temperature has dropped.” Elsewhere, it says: “Windows and other ventilation openings should not be closed, but their openings reduced when the outdoor air becomes warmer than the air indoors – this should help keep rooms cool whilst allowing adequate ventilation.”
In 1995, 739 people died in five days in a heatwave in Chicago. Many of them could not afford air conditioning and did not open their windows because they were worried about crime.
“This heat is very dangerous,” says Roaf. “If you’ve got an overheating flat or house, go somewhere else.” Go to an air-conditioned shopping centre or cinema, for example, or stay with a relative with a cooler house if possible.
If it stays very hot in your bedroom at night, move your mattress to the coolest room in the house.
Blocking out light on sun-facing sides of the house can also make a big difference. “Keeping the sunlight out will prevent some 800 watts per square metre coming through the windows,” says Roland Ennos at the University of Hull.
The best way is to have shutters fitted on the outside of windows, blocking the light before it gets into the house. If that isn’t possible, closing curtains will help.
There are other things you can do to help cool your house in the long run. Growing plants outside your house can help to shade the walls from direct sunlight, once again blocking something like 800 watts per square metre, says Ennos. “Wisteria is great up the south side, as are climbing roses, and reasonably manageable, while ivy on the other sides can help keep the house cool in summer.”
In a city like London, green roofs on buildings cool the surrounding area, lowering the peak temperature by around 4°C.
Alternatively, you could paint your house white so the walls reflect more heat, although it will need regular repainting.
If a heatwave lasts for many days, even a well-shaded house with thick walls will heat up. At this point, you might be tempted to get air conditioning. From a societal perspective, that’s a terrible idea. Air conditioners shunt hot air outside, making the surrounding neighbourhood warmer – by up to 2°C, according to one study. What’s more, they use huge amounts of energy, contributing to the burning of fossil fuels and causing more global warming.
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