Should You Sleep with the Window Open?

When a heatwave hits and your bedroom turns into a greenhouse, you find yourself wondering whether to fling the window open or keep it firmly shut. Come a cold night in January, the same question flips to fresh air against a chilly room and a bigger heating bill. It’s one of those small bedtime choices that matters more than you’d think.

So, should you sleep with the window open? For most people, the answer is yes, with a few sensible exceptions. To help you get it right, we’ve teamed up with our sleep expert, Sammy Margo, and dug into the research.

For most people, yes. A window cracked open at night pulls off two nice tricks at once: it cools the room down, and it freshens up the air you’re breathing all night. Both make a real difference to how well you rest. Our 2026 Sleep Survey found that being too hot is one of the most common reasons people cite for a broken night, with nearly 1 in 4 (24%) naming it. A slightly open window is one of the simplest ways to take the edge off.

“For most people, it is relatively risk-free and cracking the window open can have some remarkable benefits at this time of year.”

Sammy Margo, Dreams sleep expert

That said, it comes down to your own situation, and there are a handful of nights when keeping it shut makes more sense. We’ll get to those.

Here’s what a bit of overnight fresh air can do for your sleep…

Cold air can help you fall asleep faster. When your bedroom is too warm, your body can’t shed heat easily, making it harder to reach the natural dip in core temperature that triggers sleep. Heat exposure has been shown to increase wakefulness and cut into your REM and deep sleep, which is why a hot room leaves you tossing and turning. Cooler air coming in helps your body settle through the night, which is exactly what restful sleep needs. Studies also link warmer bedrooms with poorer sleep overall. Sammy Margo suggests aiming for around 16 to 18 degrees, in line with the ideal temperature for sleep.

Shut the window and, over the course of a night, the air in your bedroom goes stale. Carbon dioxide slowly builds up from your own breathing, along with dust and other fine particles. That matters more than it sounds. Higher bedroom carbon dioxide levels are linked to more night-time awakenings and shallower sleep.

In studies where people simply opened a window or a door, air quality improved, sleep improved, and people thought more clearly the next day. It’s often why a stuffy, closed-up room can leave you feeling groggy and a bit stuffy come morning. Crack the window overnight, and the fresh air keeps things clear, so you may wake up feeling brighter.

There’s something calming about drifting off to soft rain or waking to birdsong. As Sammy Margo puts it:

“Whether it’s gentle raindrops or the chirp of birds in the morning, these sounds serve as perfect natural noises to help you sleep.”

Sammy Margo, Dreams sleep expert

Raindrops and bird sounds do much the same job as the sleep apps and playlists so many of us reach for, and they cost nothing. Whether it suits you depends on where you live. A quiet garden is one thing. A main road at 2 am is quite another, which leads us neatly to the nights it’s better to keep the window shut.

For all its perks, an open window isn’t right for every home or every night. A few things are worth a quick think first.

If you get hay fever, an open window lets pollen drift in, which can flare up your symptoms and disrupt your sleep right through spring and summer. On high pollen nights, keeping the window shut may be best. If you live on a busy road, traffic noise and fine particle pollution can undo the good that the fresh air does, so the quality of the air outside is worth considering as much as the air inside. Security is another sensible thought, especially for ground-floor and easily reached windows.

Winter brings its own catch. An open window on a cold night can leave the room chilly and damp and add to condensation on the glass and walls. Airing the room well before bed, or opening the window just a crack for a short spell, gives you the fresh air without the shivering. Our season-by-season sleep guide has more on getting this balance right in the colder months.

It depends a little on the time of year and where you live. Here’s the quick cheat sheet:

A few extra habits help too. If your bedroom has only one window, opening a window in another room and leaving the doors ajar helps air move through. Pair an open window with breathable summer bedding and, on the hottest nights, a fan. For the full rundown, see our tips for keeping cool at night.