Sleeping in hot weather

In hot weather the evening often brings little relief indoors. The air outside may cool after sunset, but brick walls, roofs and floors release stored heat for hours, so a bedroom can stay warm well into the night. What you do during the day matters as much as what you do at bedtime.

Why bedrooms stay hot at night

Several things usually combine:

• Sunshine through the windows during the day, especially in west-facing rooms, which catch the sun in the late afternoon and evening.
• Heat stored in walls, floors and ceilings, which keeps coming out long after the sun has gone.
• The roof, which has been heating up all day. Loft rooms and top floors are usually the hardest to keep cool.
• Warm air rising from the rest of the house up the stairs.
• Windows kept shut at night for security or to keep out noise.

Keeping heat out during the day

Close blinds or curtains on sunny windows before the sun reaches them, not once the room is already hot. Shading outside the glass, such as shutters or awnings, stops more heat than blinds inside, because the heat never gets into the room.

Keep the bedroom windows closed while the air outside is warmer than the air inside. It can feel stuffy, but opening them lets hotter air in.

Switch off televisions, computers and other equipment in the bedroom when you're not using them. Almost all the electricity they use ends up as heat in the room. Keeping cool without air conditioning covers more ways to keep heat out of the whole house.

Ventilating at the right time

Open the windows once the air outside is cooler than inside, which on a hot day usually means late evening. Leaving them open overnight and into the early morning, where it's safe to do so, lets the building shed some of its stored heat. Close them again as the day warms up.

Air moves best when it has a way in and a way out. Opening windows on opposite sides of the house draws air through, with internal doors open while you're up. Fire services advise closing internal doors at night, so shut them when you go to bed. Lockable window restrictors let you leave a window slightly open at night without leaving it wide open.

Fans and bedding

A fan doesn't lower the temperature of a room, and its motor adds a little heat. What it does is move air across your skin, which makes you feel cooler, so it only helps while you're in its path.

At night, with a window open elsewhere, a fan facing out of an open window pushes warm air out and draws cooler air in behind it.

Lighter bedding helps too: cotton or linen sheets, and a low-tog summer duvet or just a sheet.

If the heat is affecting your health, or the health of someone you look after, follow the NHS's advice on hot weather.

Cooling the bedroom at night

The main ways of cooling a bedroom compare like this:

Air conditioning lowers humidity as well as temperature, and on a muggy night the drier air makes a noticeable difference. A few habits help it work well:

• Cool the room for a while before bed with the door and windows closed, so it's comfortable when you get in.
• Use a moderate setting rather than the lowest. Drier air feels cooler, so you rarely need a very low temperature.
• Try sleep mode. On many systems it nudges the set temperature up by a degree or two over the first few hours, lowers the fan speed and dims the display, though details vary by model. Sleep and quiet modes explains the options.
• Angle the louvres so the air doesn't blow straight onto the bed. Cool air sinks, so aiming it across the room or slightly upwards spreads it more evenly. Directing the airflow has more on this.
• Use a timer if you'd rather it switched off after you've fallen asleep, or came on before you wake.

Noise matters most in a bedroom. With a split system the compressor, the noisiest part, is in the outdoor unit, and quiet indoor units are often around 19–26 dB(A) on their lowest fan speed. A portable air conditioner has its compressor in the room with you, so it's usually louder.