What do people get wrong about the kotatsu?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
The heated low table with a quilt is one of the most photographed objects in Japanese homes. Outside Japan it reads as cosy furniture; inside Japan it is a heating strategy born of houses that were, until recently, barely insulated.
Why it exists
- Japan's housing stock is poorly insulated by rich-country standards: only about 13% of existing homes met the 1999 energy-saving insulation standard as of 2018 (Ministry of Land, Infrastructure, Transport and Tourism). New homes have been required to meet insulation standards only since April 2025.
- Heating the whole house was therefore expensive and leaky. The kotatsu — a 300–600 W heater under a table, with a quilt to trap the warmth — heats the people, allowing the room to stay around 18–20°C.
- The Ministry of the Environment's winter guidance ("Warm Biz") recommends a room temperature of 20°C as a reference.
| Item | Typical figure |
|---|---|
| Heater output | 300–600 W (thermostat-controlled, so actual draw is lower) |
| Running cost (Tokyo, 31 yen/kWh, 5 h/day) | roughly ¥15–50 per day |
| Compared with a 1,000 W fan heater, 5 h/day | roughly ¥155 per day |
[Verify] Insulation-standard figures with MLITT's housing survey; electricity rates change — recalculate costs at publication.
Misunderstanding 1｜It heats the room
It heats what is under the quilt. This is the point: head cool, feet warm is comfortable at a lower room temperature, and that is where the saving comes from.
Misunderstanding 2｜Sleeping under it is the ultimate comfort
It is the main cause of kotatsu-related harm: dehydration, low-temperature burns from prolonged contact, and in older units overheating. Manufacturers and the National Institute of Technology and Evaluation (NITE) advise not sleeping under it.
Misunderstanding 3｜Any table with a heater is a kotatsu
The modern electric type has a flat heater unit with a guard; old charcoal or "hori-gotatsu" (sunken pit) types still exist in rural houses and have carbon monoxide risk. Do not improvise one.
Misunderstanding 4｜The quilt can be any blanket
The kotatsu-gake is a quilt sized to reach the floor on all sides and made of flame-retardant or at least non-synthetic-fluff fabric. Laundry drying on or against the heater unit is a known fire cause (NITE case reports).
Misunderstanding 5｜It is only for old-fashioned homes
Sales remain steady, and compact one-person kotatsu for small flats and remote work are a growth segment. It pairs well with a sensor-controlled thermostat and a cheaper room temperature.
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Sources
- Ministry of the Environment — Warm Biz (winter energy-saving guidance, room temperature 20°C)
https://ondankataisaku.env.go.jp/coolchoice/warmbiz/
- Ministry of Land, Infrastructure, Transport and Tourism — Insulation performance of the housing stock
https://www.mlit.go.jp/jutakukentiku/house/jutakukentiku_house_tk4_000103.html
- National Institute of Technology and Evaluation (NITE) — Kotatsu accident cases
https://www.nite.go.jp/jiko/chuikanki/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
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