How to cool a bedroom for sleep in a UK heatwave

Poor sleep is often the first real cost of a UK heatwave. Bodies need to cool slightly to fall and stay asleep, and a warm, still bedroom gets in the way. The frustrating part is timing: the bedroom is frequently at its hottest just as you go to bed.

Why the bedroom is hottest at bedtime

Walls, floors and roofs soak up heat through the day and give it back for hours after the sun has gone. Upstairs bedrooms sit under the roof and above the rest of the house, where warm air collects. And if the windows were open during the afternoon, the room filled with warm air that is still there at 11pm.

A bedtime routine that works

1. 1

   All day: keep the sun out

   Blinds and curtains closed on the bedroom windows before the sun reaches them, and the door shut.
2. 2

   Early evening: cool the rest of the house first

   Open windows elsewhere as soon as the air outside is cooler than inside.
3. 3

   An hour before bed: flush the bedroom

   Open the bedroom window wide, and a window on the opposite side of the home, to pull the stored heat out.
4. 4

   In bed: move air over you

   A fan pointed across the bed helps sweat evaporate. Light cotton or linen bedding, and a thin sheet instead of a duvet.
5. 5

   Through the night

   Keep the window open if it is safe and quiet. Use a secure restrictor on the ground floor.

Nights are getting warmer

A tropical night is one where the temperature does not fall below 20°C. They are rare in the UK now, but the Met Office's local projections for Westminster rise from about 1 a year in the 2001 to 2020 climate to about 4 at 2.5°C of global warming, and about 15 at 4°C. On those nights, opening the window stops being enough, because the air outside is not cool.

Who is most at risk

Hot bedrooms are more than uncomfortable for older people, babies and young children, and anyone with heart, lung or kidney conditions, because their bodies cope less well with sustained heat. If someone like that sleeps in the hottest room in the house, it is worth moving them to a cooler one during a heatwave, and the checker lets you flag a heat-vulnerable occupant so it weighs the risk accordingly.

When a bedroom needs a system

If the bedroom regularly stays above 26°C at night despite shading and ventilation, a small wall-mounted unit is the most effective fix, and usually only a 2.0 or 2.5 kW unit for a typical bedroom. Run it for the first part of the night at 24°C to 26°C rather than all night at a low setting: it is quieter, cheaper and easier to sleep with.