Nine Small Changes That Make a Bedroom Cooler at Night
Sleep quality falls off sharply above roughly 20 °C in the bedroom. Most homes can get closer to that without buying anything.
Heat disrupts sleep in a specific way: your body needs to shed about a degree of core temperature to fall asleep and stay asleep, and a hot room makes that slow and unreliable. The good news is that a bedroom is a small, closable space — the easiest room in a house to control.
1. Shade the window from the outside if you can
Once sunlight passes through glass, most of its energy is already in the room. External shutters, awnings or even a temporary outdoor screen block far more heat than any interior curtain. Where external shading is impossible, light-coloured blinds closed before the sun hits the window still help considerably.
2. Close the house during the day, open it at night
Track when the outdoor temperature drops below the indoor one — usually a couple of hours after sunset — and open up then. Opening windows in the afternoon of a hot day actively imports heat.
3. Create a cross-draught, not just a fan
A fan pointed at an open window on the cooler side, with another opening on the opposite side of the home, moves far more air than a fan pointed at the bed. The aim after sunset is to flush warm air out of the building rather than stir it around.
4. Turn off what is heating the room
A games console, a desktop computer, a television on standby and a phone fast-charging on the nightstand all convert electricity into heat inside a small room. So does incandescent lighting. None of them is dramatic alone; together they are noticeable in a 12 m² bedroom.
Fans cool people, not rooms. Leaving one running in an empty bedroom all day slightly warms it. Run it when you are in the room.
5. Change the bedding, not just the temperature
Cotton percale, linen and bamboo-derived fabrics move moisture better than microfibre or satin polyester. A lighter duvet — or two single duvets instead of one shared — changes perceived warmth more than most people expect. Memory foam mattresses retain heat; a cotton mattress protector or a thin topper helps.
6. Cool yourself before bed, gently
A warm — not cold — shower an hour before bed brings blood to the skin and helps the body shed heat afterwards. A cold shower does the opposite by constricting surface blood vessels. Damp hair, a cool flannel on the wrists or neck, and cotton nightwear all work through the same mechanism.
7. Watch the humidity, not just the thermometer
At high humidity, sweat evaporates poorly and 26 °C feels considerably worse than the same temperature in dry air. Drying laundry indoors in the bedroom, or running an evaporative cooler in a sealed room, both push humidity up. A cheap hygrometer tells you whether that is your problem.
8. Deal with the roof
Top-floor and attic bedrooms are hot because the roof space above them stores the day's heat and radiates it back after dark. Loft insulation is the single most effective intervention available, and it works in both directions — cooler in summer, cheaper to heat in winter.
9. Sleep low, and alone if you can
Warm air stratifies. In a room with a high ceiling or a mezzanine, the sleeping surface closest to the floor is measurably cooler. Two adults in a bed generate roughly double the heat of one — in a serious heatwave, temporarily separating is a legitimate and effective solution.
None of these replaces air conditioning in an extreme heatwave. What they do is lower the baseline, which is worth having on its own — and if you do use a cooling appliance, it will reach a comfortable temperature faster and run less to hold it.