Must you set the bedroom to exactly 18°C to sleep well? This is a practical value often recommended in France, but it is not a universal biological temperature. Comfort also depends on your duvet, nightwear, humidity, air circulation, age and health.
Why do we often sleep better in a fairly cool room?
Core body temperature follows a daily rhythm. As sleep approaches, the body promotes heat loss, especially through the hands and feet. This reduction accompanies sleep onset; it is not caused only by the room thermostat.
The environment can nevertheless help or interfere. In very warm conditions the body loses heat less easily. Sleep may become more fragmented and some stages may change. If the room is too cold and bedding does not compensate, discomfort and thermoregulatory responses can also cause awakenings.
Air temperature is only part of the picture. A warmer microclimate forms under the duvet. A cool bedroom with a highly insulating duvet may feel too warm; a 20°C room with a light sheet may be comfortable. Two people exposed to the same thermostat can therefore have very different nights.
18°C: useful recommendation or magic number?
Assurance Maladie cites a temperature around 18°C for cooling the bedroom, including in advice about sleep problems during menopause. France’s energy agency ADEME recommends about 17°C in bedrooms overnight in its heating guidance. These values balance comfort, sleep and energy use.
Use 18°C as a starting point, not a guaranteed result. If you are comfortable, do not sweat and do not wake because of cold, there is no need to chase a lower number. If you feel cold despite suitable bedding, raise the temperature slightly.
Research does not identify one number for the whole population. A study of fifty older adults living in Boston observed the most efficient sleep between 20 and 25°C, with efficiency falling as temperature moved away from that range. This is interesting for older people but cannot become a universal recommendation: the sample was small and specific, and participants lived in real homes with different habits.
Other work stresses the interaction between room temperature, clothing and bedding. The sound conclusion is less spectacular than one precise number: avoiding excessive heat and thermal discomfort generally supports sleep.
| What you notice | Possible factor to test | First adjustment |
|---|---|---|
| Sweating or throwing off the duvet | Room or bedding too warm | Remove one layer before cooling aggressively |
| Cold feet or shivering | Insufficient insulation | Add a breathable layer or raise heating slightly |
| Stuffy air on waking | Insufficient ventilation | Air the room when outdoor conditions allow |
| Two people disagree | Different needs or duvets | Use separate, adjustable covers |
How can you find your personal temperature?
1. Begin with a stable reference point
Choose a realistic temperature, such as 18°C during the heating season, and keep it for several nights. Changing the heating, duvet, nightwear and bedtime together makes the effect impossible to interpret.
2. Look at the right signals
- do you feel hot or cold when you get into bed?
- do you wake sweating, shivering or with a very dry mouth?
- do you often throw off the duvet?
- does your partner feel the same?
- do awakenings occur only in certain weather?
How you feel on waking and a repeated pattern across several nights are more useful than one measurement. If you wake despite a comfortable temperature, explore other common causes of night awakenings.
3. Adjust one degree or one layer
Change either temperature or bedding slightly, then observe three to five comparable nights. If you are too warm, start with a less insulating duvet, lighter nightwear or improved air flow. If you are cold, add a layer rather than overheating the entire room.
4. Separate the room from the bed
Breathable, dry bedding helps regulate the microclimate. A product’s “cooling” marketing claim does not prove a clinical benefit. Test what actually reduces sweating or discomfort for you.
For couples, separate duvets can let each person choose insulation without imposing the same thermal sensation. This is not a sleep treatment, simply a practical adjustment.
How can you sleep on a hot night?
When outdoor temperatures remain high, reaching 18°C may be impossible or use excessive energy. The aim then is to limit heat accumulation and help it dissipate.
- Block heat during the day. Close shutters or solar blinds when sunlight reaches the windows.
- Ventilate at the coolest time. Open windows when outside air is genuinely cooler and noise, pollution or allergies allow.
- Move the air. A fan can improve comfort without lowering measured temperature as much. Position it to avoid a permanently unpleasant draught.
- Use lighter bedding. Choose thin layers that can be replaced if temperature drops overnight.
- Hydrate normally. Avoid drinking a very large quantity just before bed if that creates repeated bathroom visits.
A lukewarm shower may be more comfortable than an ice-cold one, especially if intense cold triggers a subsequent warming response. The aim is to reduce discomfort, not cause thermal shock.
Special cases: age, menopause and illness
Thermoregulation changes with age and circumstances. Older people may be more vulnerable to cold or heat. Menopausal hot flushes, fever, some medicines, hyperthyroidism or hypoglycaemia can also cause night sweats. Adjusting the room may improve comfort without treating the cause.
An adult bedroom guide should not automatically be applied to a baby, a frail person or someone with a condition affecting body temperature. Use recommendations specific to the situation and seek professional advice.
Key points
- Around 18°C is a practical guide for an adult bedroom in France.
- There is no single proven perfect temperature for everyone.
- Duvets, clothing and air circulation matter as much as the thermostat.
- Test one adjustment at a time across several nights.
- Persistent thermal discomfort may indicate more than a poor setting.
Scientific and institutional sources
- Assurance Maladie — Advice for sleeping better during menopause.
- ADEME — Recommended temperatures in the home.
- CDC — Habits that support good-quality sleep.
- Okamoto-Mizuno and Mizuno — Effects of thermal environment on sleep (2012).
- Baniassadi et al. — Night-time temperature and sleep in older adults (2023).
- Mayo Clinic — Creating a cool, dark and quiet environment.