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We've seen heatwaves in the US and the UK already this year, and while that might be great for a day at the beach or park, it's not ideal for sleeping. Especially if you're one of countless people making a common yet key mistake with your bedroom window that unintentionally makes your bedroom even hotter during a heatwave.After staying in a beautiful, but particularly hot, rental property in the UK for a week as temperatures soared during a record-breaking May heatwave, I learned a bedroom window hack that can help keep you cool at night. And here I've spoken to sleep and home experts about why it actually works.Read on to find out what key bedroom window mistake you should avoid at night during a heatwave, and what to do instead to keep your sleep space cool.Key takeaways: At a glance The key mistake – Keeping the bedroom window and curtains/blinds open during a heatwave is the most common mistake people make.Why it's a mistake – When the temperature is hotter outside than indoors, you're actually allowing warm air into the room, while open curtains/blinds allow sunlight in that can also heat up your sleep space.The fix – Keep windows and curtains/blinds closed during hot weather, opening them when the air is cooler in the evening. You can also use tin foil on windows during very hot weather, but this is only a temporary solution.The temperature thresholds – You must close up your bedroom the moment the outdoor temperature exceeds the indoor temperature. As a rule of thumb, experts recommend sealing the room once outdoor temperatures reach 22°C to 25°C in the UK, or 79°F in the US (the official indoor limit recommended by the World Health Organization). At this point, your walls begin to hold heat.Beware hidden heat traps – these include bedroom electronics on standby, memory foam mattresses, and thick bedding, non-breathable bedding.The key bedroom window mistake people make during a heatwave
