A low Japanese table with a built-in heat source: a heater sits under the tabletop, and a thick blanket is draped over the frame outside, holding warmth around your legs. The rest of the room stays cold.

How does a kotatsu warm your legs and not the whole room?

The heater — once a charcoal brazier, now usually an electric coil — sits inside the frame under the blanket, and the warmth stays in that enclosed space around the legs of those sitting there. The air in the rest of the room does not change, so you crawl under the kotatsu rather than heating the whole house.

Is it dangerous to sleep under a kotatsu?

A folk belief says that falling asleep under the blanket during the day will give you a cold: your body warms up under the kotatsu while your head and shoulders stay in the cold air. Old charcoal models also carried a real risk — carbon monoxide poisoning in an unventilated room — which is why modern kotatsu are almost always electric.

How does 掘り炬燵 differ from an ordinary kotatsu?

In an ordinary portable kotatsu (置き炬燵) you tuck your legs on a flat floor, as at any low table. In a kotatsu cut into the floor (掘り炬燵), a pit is cut under the frame, and you sit in it with your legs hanging down, almost as if on a chair.

Does the kotatsu mean that Japanese homes are not heated all over?

In most of Japan, except the cold north, homes are indeed heated in parts rather than as a whole, and the kotatsu is just such local heating. A telling exception is Hokkaido: there homes are built airtight and centrally heated, so kotatsu are kept there least of all in the country.

Do kotatsu exist in today's Japanese apartments?

Yes, the kotatsu is not a museum piece: it is still sold and kept at home, though after the spread of air conditioners from the 1970s interest in it declined noticeably compared with its peak. Many families keep the table year-round, simply removing the warm blanket in summer.

Kotatsu: the heated table you never want to leave in winter

A kotatsu is a low Japanese table with a built-in heat source: inside the frame sits a heater — once a charcoal brazier, now usually electric — and a thick quilted blanket is draped over the frame on top. You tuck your legs under the blanket, toward the warmth, while the rest of the room stays cold. In winter the whole family gathers around one kotatsu, eats mandarins, and often falls asleep right there.

The word "kotatsu" often brings up online shops selling heated tables, but in Japan it is not a product so much as a part of winter life with centuries of history. The word also has its own linguistic story: the character 燵, which appears in no other Japanese word. Let's look at what a kotatsu is made of, how it is used in winter, and why electricity reached it so late.

What a kotatsu is made of: frame, blanket, and tabletop

A kotatsu is a low table with a built-in heat source. Inside the frame, the yagura, sits a heater — once a charcoal brazier, now usually electric. A thick blanket, the kotatsu buton, is draped over the frame, and a removable tabletop, the tenban, is placed on top of the blanket. You tuck your legs under the blanket, toward the warmth, while the rest of the room stays cold: a kotatsu warms the person, not the air in the room.

Frame (やぐら, yagura) — the structure inside which the heater is mounted.
Heater — once charcoal or a tadon brazier, now usually an electric coil.
Blanket (こたつ布団) — a thick quilted cover that holds warmth around your legs.
Tabletop (天板) — a flat panel over the blanket: you eat, write, and play cards on it.

A table for all year, not just winter

In summer the blanket comes off, and the frame with the tabletop becomes an ordinary low table. Many families keep a kotatsu in the room year-round rather than putting it away in spring with the winter things.

Winter life around a kotatsu: mandarins, the cat, and the difficulty of getting up

On a winter evening the whole family gathers under one blanket: watching TV, peeling mandarins, talking. The warmth stays only under the table, so you want to burrow deeper and never leave. Hence the folk belief that falling asleep under a kotatsu during the day will surely give you a cold: your body warms up under the blanket while your head and shoulders stay in the cold air.

The family cat almost always finds a spot under the kotatsu blanket and is in no hurry to leave it.
A portable kotatsu (置き炬燵) can be moved to any room — you simply place a brazier under it or turn on an electric heater.
A kotatsu cut into the floor (掘り炬燵) is built differently: a pit for the legs is cut under the frame, and you sit in it as if on a chair rather than tucking your legs on a flat floor.

Why it is hard to get up from a kotatsu

The reason is not the design but the contrast: under the blanket, warmth stays tightly around your legs, while just beyond its edge is the ordinary cold air of an unheated room. For a stubborn homebody who never leaves the kotatsu in winter, Japanese has a special word — 炬燵弁慶, "kotatsu-benkei." According to the Edo-period dictionary 物類称呼, this was the name for old men who did not get up from under the blanket all winter.

From a hearth under a frame to an electric coil: the history of the kotatsu

The earliest written mention of a kotatsu is an entry from October 1490 in the diary of the Kyoto temple 蔭凉軒日録. By the end of the 15th century such devices were already known in Kyoto. The first form was a frame placed directly over an open irori hearth and covered with a blanket, while the low version for sitting on a chair is thought by one account to have been brought to Japan from China in the Muromachi period.

Cotton for quilted blankets began to be imported to Japan only in the 16th century, so the current look of a kotatsu with legs under a blanket reaching the knees or waist spread only from the 17th century, in the Edo period.
In the middle of the Edo period, a portable kotatsu with a brazier inside instead of a hearth appeared — unlike the one cut into the floor, it could be carried to another room.
The enclosed space under a blanket with smoldering charcoal is poorly ventilated, and a charcoal kotatsu carried the same risk of carbon monoxide poisoning as any hearth in a closed room.

Electricity reached the kotatsu late

An electric heater for the kotatsu was tried as early as the 1920s, but it sold poorly. The truly electric version spread across the country only in 1957, when Toshiba released a kotatsu with a nichrome-coil heater, and since then electricity has remained the main source of heat.

燵 — a character found in no other word

燵 — значение: foot warmer (only in this word), part of the word 炬燵 — онъёми: タツ — 17 штрих(ов). 燵 is a kokuji, a character invented in Japan specifically for this word: it has no kun reading, only the on reading タツ, and it appears almost nowhere outside 炬燵.

Fire and confusion over old spellings

The first character of the word, 炬, by itself means "torch, signal fire" and in this word is read ko. For a long time the kotatsu had no fixed spelling: in texts from the Muromachi and Edo periods there are variants 火闥, 火踏, 火燵, and 巨燵, and only later did the current 炬燵 become established. By one account the word goes back to 火榻 ("fire couch"), but this is only a hypothesis, not a proven fact.

Japanese	Reading	Translation
こたつ	kotatsu · kotatsu	Kotatsu
こたつ布団	kotatsu buton · kotatsu buton	Kotatsu blanket
天板	tenban · tenban	Removable kotatsu tabletop
掘り炬燵	horigotatsu · horigotatsu	Kotatsu with a leg pit

Trace 燵 along the guides — a character found only in the word "kotatsu."

FAQ

What is a kotatsu?: A low Japanese table with a built-in heat source: a heater sits under the tabletop, and a thick blanket is draped over the frame outside, holding warmth around your legs. The rest of the room stays cold.
How does a kotatsu warm your legs and not the whole room?: The heater — once a charcoal brazier, now usually an electric coil — sits inside the frame under the blanket, and the warmth stays in that enclosed space around the legs of those sitting there. The air in the rest of the room does not change, so you crawl under the kotatsu rather than heating the whole house.
Is it dangerous to sleep under a kotatsu?: A folk belief says that falling asleep under the blanket during the day will give you a cold: your body warms up under the kotatsu while your head and shoulders stay in the cold air. Old charcoal models also carried a real risk — carbon monoxide poisoning in an unventilated room — which is why modern kotatsu are almost always electric.
How does 掘り炬燵 differ from an ordinary kotatsu?: In an ordinary portable kotatsu (置き炬燵) you tuck your legs on a flat floor, as at any low table. In a kotatsu cut into the floor (掘り炬燵), a pit is cut under the frame, and you sit in it with your legs hanging down, almost as if on a chair.
Does the kotatsu mean that Japanese homes are not heated all over?: In most of Japan, except the cold north, homes are indeed heated in parts rather than as a whole, and the kotatsu is just such local heating. A telling exception is Hokkaido: there homes are built airtight and centrally heated, so kotatsu are kept there least of all in the country.
Do kotatsu exist in today's Japanese apartments?: Yes, the kotatsu is not a museum piece: it is still sold and kept at home, though after the spread of air conditioners from the 1970s interest in it declined noticeably compared with its peak. Many families keep the table year-round, simply removing the warm blanket in summer.

Sources

Updated: 2026-09-21