The Best Bedroom Temperature for Sleep
To fall asleep, your body has to cool down: core temperature drops by roughly a degree as you drift off, and the room either helps that heat escape or fights it. That is why a bedroom at 24 °C feels fine for reading but miserable for sleeping — and why the thermostat number is only half the story.
Why cool rooms make sleep easier
Your body sheds heat through your skin, mostly via the hands, feet and face that stick out of the duvet. A cool room keeps that heat flowing outward all night; a warm one blocks the exit. Somewhere around 17–19 °C is commonly recommended for adult bedrooms — cool enough to dump heat, warm enough that you’re not tensing up under the covers.
The exact number is personal. Duvet thickness, pyjamas and metabolism all shift it. The useful signal is simple: if you wake up sweaty or keep pushing the duvet off, the room is too warm for how you sleep.
Humidity is the hidden half of comfort
Two rooms at 20 °C can feel completely different. When you get warm at night, your body sweats and counts on that sweat evaporating; humid air slows the evaporation, so the same temperature feels hotter and stickier. Dry air at 20 °C is a pleasant night — muggy air at 20 °C is a wrestling match with the sheets.
For comfort, keeping indoor relative humidity roughly between 40 and 60% is the usual guidance. But be careful when deciding whether to open the window to fix it: what matters is how much water the outdoor air actually holds in absolute terms (g/m³), not its percentage. Muggy evening air can read a harmless-looking RH while carrying more water than your bedroom air.
Getting the bedroom cool without AC
In summer the problem is timing. Walls and furniture soak up heat all day and release it back in the evening — that thermal lag is why your bedroom is still an oven at midnight even after the outdoor air has cooled.
The routine that works:
- Shut and shade all day. Windows closed, shutters or blinds down on the sunny side, from mid-morning onward.
- Open wide when outside is genuinely cooler and drier. Usually late evening through early morning. Night airing is when the real cooling happens — cross-draft if you can.
- Shut again before the morning warm-up. Trap the cool air and the walls’ overnight losses before the sun reverses the flow.
In winter: cool, yes — damp, no
A cool bedroom in winter comes with a catch. You exhale water vapour all night — roughly a fraction of a litre per sleeper — and cool air holds less of it, so the RH climbs and the coldest surfaces flirt with the dew point. That’s the recipe for wet window corners and, eventually, mold behind the headboard.
The fix isn’t heating the bedroom to 22 °C. It’s a short, wide-open airing every morning to flush out the night’s moisture while the walls keep their warmth — the routine that keeps bedroom mold away. Cool and dry is healthy; cool and damp is not.
Let the app watch for you
The right moment to open the bedroom window shifts with every evening’s weather. Open/Shut compares outdoor temperature and absolute humidity with your home’s and tells you when opening will actually cool and dry the room — and when to keep it shut. Free, private, no account.