Bedroom 18°C, living room 21°C — why the recommendations differ
Every year in mid-October the same household argument returns. One person sets the thermostat to 21 degrees and says it is cold. The other opens the bedroom window and says sleep is impossible. Both are right, because they are talking about two different rooms and two different bodily states.
Why the body needs cool to fall asleep
Falling asleep does not begin in the head. It begins with a drop in core body temperature of roughly 0.5 to 1 degree Celsius. That drop is one of the signals that initiates sleep — and it has been well documented in sleep physiology since the 1990s, notably in the work of Kräuchi and Wirz-Justice in Basel.
The mechanism is surprisingly concrete. For core temperature to fall, the body has to shed heat — and it does so by dilating the blood vessels in hands and feet. That is why cold feet make falling asleep harder: not because it is unpleasant, but because constricted vessels block heat's escape route. And it is why a warm bath 90 minutes before bed helps — it does not warm you, it pushes blood to the skin, and once you are out of the tub the body sheds heat faster than usual.
This is where the 18°C bedroom recommendation comes from — repeated by most sleep medicine societies, usually as a 16–19°C range. It is the temperature at which the surroundings draw heat away fast enough, but not so fast as to cause shivering.
Why the living room is 21, not 18
In the living room you are in a different state. You are sitting or standing, wearing one layer, with no insulation over you, and your metabolism during the day runs more than ten percent higher than in the middle of the night. Under those conditions 18 degrees simply means you are cold.
Polish building regulations reflect this: the design temperature is 20°C for living rooms and bedrooms, 24°C for bathrooms, and 16°C for corridors and utility rooms. The differences are not arbitrary — they follow from how much heat you shed and how much you are wearing.
| Room | Recommended temperature | Why |
|---|---|---|
| Bedroom (at night) | 16–19°C | Metabolism at its minimum, insulation over the body |
| Living room | 20–22°C | Sedentary, one layer of clothing, no insulation |
| Bathroom | 23–24°C | Wet skin sheds heat through evaporation |
| Child's room (at night) | 18–20°C | Smaller body mass, faster heat loss |
| Hallway | 16°C | Short stays, movement |
What each degree costs
This is the part most people care about this season. The estimate used by European energy agencies is that lowering the temperature by 1°C cuts heating energy use by about 6 percent. For a Polish flat with an annual heating cost around 2,500 zł, that is roughly 150 zł per degree.
But there is a catch that is rarely spelled out. That saving applies to the daily average temperature, not to turning a radiator down for one night. A concrete-framed block of flats has high thermal inertia — turn the radiator off at 22:00 and the temperature may drop one degree by three in the morning, and you will have to heat it back up. In a well-insulated building a night-time reduction of 2–3 degrees makes sense; in an old, uninsulated building with cast-iron radiators the effect can be close to zero.
The practical version: if you have a programmable thermostat, set a reduction from 22:00 to 5:30 and check after a week whether the mornings are too cold. If you do not, turning down the radiator in the bedroom alone works better than manoeuvring the whole flat.
The humidity everyone forgets
The recommended band is 40–60 percent. During the heating season in Polish flats it usually falls to 25–35 percent, because heating dries the air. Symptoms: a dry throat on waking, irritated eyes in the morning, static bedding.
The opposite problem — above 60 percent — is more dangerous to the flat than to you. At 18 degrees and high humidity, vapour condenses on the coldest surfaces: in the corners of external walls, behind wardrobes, on window reveals. This is the classic mould mechanism in Polish blocks, especially after replacing windows with airtight ones without fitting trickle vents.
If you are lowering the bedroom temperature, ventilate briefly and intensively — five minutes with the window wide open once a day exchanges the air more effectively and more cheaply than a tilted window all day, because it does not chill the walls.
Where the blanket fits in
Here we reach the heart of it. The “18 degrees” recommendation assumes that a microclimate at a completely different temperature forms under the covers. Research on bed climate shows that the comfortable air temperature right at the skin under bedding is roughly 31–35°C, at humidity below 60 percent. The gap between room and bed is more than ten degrees, and bedding is what creates it.
A weighted blanket enters this equation twice. First as insulation — layers of non-woven fabric with microbeads are thicker than an ordinary all-season duvet, so at the same room temperature it will be warmer underneath. Second as a barrier to water vapour: if the cover is polyester, moisture has nowhere to go, and you get that clammy heat around three in the morning even though the room is cool.
Practical conclusion: in an 18-degree room a weighted blanket in a cotton cover is usually enough on its own, with no extra throw. In a 21-degree room the same blanket is often too warm, and it is better to go one weight down or switch to a waffle cover, which holds more air and releases it faster.
A plan for the first week of the heating season
- Buy a thermometer with a hygrometer for the price of a coffee and put it in the bedroom at bed height, not next to the radiator.
- Change nothing for three nights — just note the temperature at 23:00 and at 6:00.
- Lower the bedroom setting by one degree and give yourself three nights to judge. Do not change two things at once.
- If you wake up overheated, go lower on temperature before you start changing the blanket.
- If you wake with cold feet, socks work better than raising the temperature of the whole room, and they are free.
- Check the humidity. Below 35 percent, put a bowl of water by the radiator or run a humidifier.
Frequently asked questions
Isn't 18°C too cold for a child?
For a child the figure is slightly higher, 18–20°C, because less body mass means faster heat loss. More useful than the thermometer is checking the back of the child's neck — warm and dry means all is well. Cold hands and feet in a sleeping child are normal.
Is turning the radiator off at night worth it?
In a well-insulated building yes: a 2–3 degree reduction over seven hours gives a real saving. In older construction with high thermal inertia the effect is small, and morning reheating can eat it. Test it against your own bill over two weeks.
Why do I wake at 3–4 am overheated when the room is cool?
Usually because of moisture trapped under the covers, not temperature. Check what your cover and pyjamas are made of — polyester in both places at once is a classic cause. The second possibility is too thick a layer: a weighted blanket plus an extra throw is usually too much in an 18-degree room.
What temperature if two of us sleep together?
Two people under one blanket generate more heat and vapour, so the lower end of the range usually works, 16–18°C, with a cover made from a fabric that moves moisture well. If one of you is cold and the other overheats, two separate blankets settle that argument more effectively than a thermostat.
Summary
Bedroom and living room carry different recommendations because you are in a different state in each: at night your metabolism is at its lowest and there is insulation on top of you. Falling asleep requires a 0.5–1°C drop in core temperature, and heat escapes through hands and feet — hence “cool room, warm feet”. Each degree lower is about 6 percent of heating cost, but what counts is the daily average, not one turned-down radiator. And in a cool bedroom, comfort is decided not by how thick the blanket is but by whether the cover moves moisture away.
Sources
- Kräuchi K., Wirz-Justice A., work on thermoregulation and sleep onset, Chronobiology International and American Journal of Physiology, 1994–2007
- Okamoto-Mizuno K., Mizuno K., “Effects of thermal environment on sleep and circadian rhythm”, Journal of Physiological Anthropology 2012;31:14
- Polish technical building regulations — design temperatures for rooms
- Per-degree energy use estimates — European energy efficiency agencies
See also
- Glass beads or pelletsThe fill is insulation too
- Aura ComfortCrinkled satin — breathes, unlike fleece
- Weight calculatorWarmer room? Go lighter
A cooler room needs a better blanket, not a warmer one
Aura Comfort and Aura Family are made from crinkled cotton satin — a fabric that releases moisture and does not trap heat the way polyester fleece does. That lets you keep the bedroom at 18°C without waking up cold at four in the morning. Sewn in Poland. Courier or InPost parcel locker delivery, 14 days to return, free weight exchange within that period.
This article is informational and concerns sleep comfort and general wellbeing. A weighted blanket is not a medical device and does not replace consultation with a specialist.