Heatwave advice: Should we keep our windows open or closed in hot weather?

Windows open or closed in hot weather? (Getty Images)
Is it better to have windows open or closed in hot weather? (Getty Images)

We know reaching for the fan, an ice lolly and drinking plenty of water are surefire ways to stay cool indoors, but the question of whether to keep windows open or closed in hot weather still trumps us.

But with an extreme heat warning issued by the Met Office, we don't want to make any mistakes in the measures we take to reduce our body temperature.

"The Amber warning, which has been issued for Sunday (17 July) and Monday (18 July), highlights likely adverse health effects for the public, not just limited to those most vulnerable to extreme heat," it says.

"Temperatures could be in excess of 35°C in the southeast, and more widely around 32°C within the warning area."

So, we might think that cracking as many windows open as we can, and letting in the 'breeze' is a safer bet then sweltering inside with no air, right? Luckily, the NHS' George’s, Epsom and St Helier Hospitals Group has helped to clear things up, with some advice on staying safe in the sun.

Read more: Heatwave insomnia: 32 tips and tricks to help you sleep during hot weather

Should windows be open or closed when hot?

Window open hot day. (Getty Images)
Is your go-to method only making you hotter? (Getty Images)

While some advice says to shut windows, and some says to open them, it seems getting the balance just right is key.

"Keep windows closed when the room is cooler than outside, but open them at night when the temperature has dropped," the hospital group says.

So, when the air is hotter outside, having windows shut is a safer bet, followed by opening them in the evening and when you sleep for some ventilation.

NI Direct government services echoes this hot weather advice but adds "open them if the room gets too hot" and "close ground floor windows when you leave the house or go to bed".

Read more: How hot does it have to be for schools and offices to close in a heatwave?

How can I know if it's hotter outside or inside?

Thermometer in garden. (Getty Images)
How sweaty you are coupled with some thermometers can help you know when to adjust your windows. (Getty Images)

While stuck indoors working or looking after children during this heatwave, there's no doubt it's going to feel pretty hot most days, and tricky to tell for sure by just sticking your arm out the window whether 'out or in' is cooler.

While this DIY method can help to give us a hunch, placing a thermostat or thermometer both inside your home and outside, whether in your garden, on your balcony, or just on your window ledge, can help you to be sure of the difference, and act accordingly.

Read more: Your sun protection guide: SPF, UVB and UVA explained

Should curtains be open or closed in hot weather?

Man closing curtains. (Getty Images)
Some curtains should be closed, and some should be left open. (Getty Images)

It seems just shutting the windows when it's hotter outside might not be enough though.

"Close curtains on rooms that face the sun to keep indoor spaces cooler and remember it may be cooler outdoors than indoors," advises the NHS Hospitals Group.

Hopefully, not all your windows face then sun and you'll still be able to have some natural light coming in...

However, NI Direct has the answer to solve this too. "Close pale-coloured curtains – closing dark curtains and metal blinds can make rooms hotter," it urges. So there's no need to close every sun-facing window.

Now you know whether it's better to have windows open or closed when hot, hopefully you'll feel that couple of degrees cooler...

The full list of tips for staying safe in the sun from the Hospitals Group include:

  • Look out for people who may struggle to keep cool and hydrated, such as elderly relatives or neighbours

  • Keep windows closed when the room is cooler than outside, but open them at night when the temperatures has dropped

  • Close curtains on rooms that face the sun to keep indoor spaces cooler and remember it may be cooler outdoors than indoors

  • Drink plenty of fluids and avoid excess alcohol. Take water with you, if travelling

  • Try to keep out of the sun between 11am and 3pm

  • Stay in the shade

  • Apply suncream regularly, and wear a hat

  • Don’t exercise during the hottest parts of the day

  • Have cool showers or baths, put a loose, cotton, damp cloth or scarf on the back of the neck, and spray or splash your face with cold water frequently to help keep your body cool.

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