How do I keep a bedroom cool enough to sleep in?

A bedroom that is unbearable at midnight was decided at two in the afternoon. Once the room and its contents are hot, there is very little that helps quickly — so nearly all of the useful action happens hours before bedtime.

Safety

Step by step

1. Shade the room from first thing.Curtains or blinds closed all day, before the sun reaches that side. A bedroom is empty during the day, so there is no cost to keeping it dark.
2. Keep the door and windows shut while it is hotter outside.Treat the room as sealed through the day. Every hour it stays shut is an hour it is not gaining heat from the rest of the house.
3. Open it fully as soon as outside is cooler.Usually mid to late evening. Open the bedroom window and one on the other side of the house or landing so air actually moves through rather than sitting.
4. Position the fan to exhaust, not to blow at you.A fan in the window facing outwards pushes the hot air out and pulls cooler air in from elsewhere. That changes the room temperature; a fan aimed at the bed only changes how you feel.
5. Then add a second fan for airflow over the bed if you want one.Once air is moving through the room, a gentle breeze across the bed helps sweat evaporate, which is the actual cooling mechanism. Low speed is enough and much quieter.
6. Strip the bedding back.A single cotton or linen sheet. Natural fibres move moisture away; polyester bedding and mattress protectors trap it and are a common hidden cause of overheating.
7. Check the mattress and protector.Memory foam retains heat noticeably, and a waterproof protector is a plastic layer under you. A cotton topper over either makes a real difference.
8. Cool yourself rather than the room.A cool — not cold — shower before bed, and a damp flannel on the wrists, neck or ankles. Cooling the blood at the surface works faster than cooling the air.
9. Turn off everything in the room.Chargers, standby lights, a television. Small heat sources matter in a sealed room over eight hours.
10. Deal with the loft above.An upstairs bedroom under a poorly insulated loft is heated from above all evening. Insulation depth is the single biggest structural fix for a hot bedroom.

Tips

• Put the fan on a timer for an hour or two. It gets you to sleep, and the noise and draught stop before they wake you at four.
• A hot water bottle filled with cold water and put in the freezer for an hour is a genuinely effective bed cooler.
• If one room is always the hot one, sleeping downstairs for a few nights in a heatwave is a reasonable answer rather than a defeat.

Common mistakes

• Opening the bedroom window during the day to air it — It fills the room with hot air, which the furniture and mattress then absorb and release all night.
• Pointing the only fan at the bed — It makes you feel cooler while the room stays exactly as hot. Use it to move air out of the window first — the two-fan arrangement is much better than either alone.

If it doesn't work

Questions people ask