‘I’ve been opening my windows wrong all this time!’ This smart trick is the fastest way to cool down a room in the evening without AC

I’ve lived in flats with large sash windows for the last four years, however, it wasn’t until the first heatwave of this year that I discovered I’d been opening them wrong all this time, and not taking advantage of their in-built cooling design feature.

I’d always believed I could only open my sash windows from the bottom. So my mind was blown when I discovered not only do they open at the top, but that the most efficient way to cool down a room and keep a bedroom cool was to open sash windows at the top AND bottom. I’ve been testing this trick out for the last few weeks, and can vouch for its effectiveness.

Sash windows are typically found in period homes, and this hidden trick would have been what the Georgians and Victorians used to keep cool before the age of the best air conditioners and electric fans.

(Image credit: Future PLC / Carolyn Barker)

‘Opening sash windows at both the top and bottom is one of the most effective ways to naturally cool a room,’ agrees Jo Trotman, marketing manager at The Residence Collection, which specialises in windows and doors.

‘This method creates a convection flow: warm air rises and escapes through the top opening, while cooler air is drawn into the room through the bottom.’

‘This continuous airflow helps regulate the temperature more efficiently than opening just one part of the window. It’s a simple yet clever feature that makes sash windows not only timeless in style but also smart in function, especially during warmer months.’

Yvonne Keal, product expert at Hillarys, a window dressing brand, agrees, saying: ‘This simple method is a great way to make the most of your sash windows and keep your home cool naturally.’

(Image credit: Future PLC / David De Lovatti)

I’ve been using this trick for the last few weeks in the evening to help quickly cool down my bedroom before going to bed. I don’t have the space or budget to invest in an AC unit at the moment, but this has done the trick of cooling my bedroom down quickly to make it a better temperature to sleep.

However, note that it will only work effectively if the air is cooler outside, which usually happens in early mornings and evenings.

If you don’t have sash windows, you can mimic the effect by opening a higher-up window and a nearby lower window to create the same convection flow. Alternatively, you can try to create a wind tunnel to force the air flow through by opening windows (or a door) on opposite sides of a room.

(Image credit: Future PLC / David Giles)

I have been encouraging the flow of air and the cooling effect by positioning a fan in front of the open bottom part of the sash window to help draw the cold air in. If you have a second fan, you can also try positioning it facing out of the window to force out the lingering hot air.

Boost the effect

Were you already in the know about this sash window cooling trick?