Under the tabletop of a kotatsu sits a small heater, and a futon hangs over the table edge to keep the heat from drifting off. The legs and lower body get warm. The rest of the room stays as cool as it was.

The floor-standing version is the okigotatsu, and the one built over a pit cut into the floor is the hori-gotatsu. Either sits on tatami through the winter with the household around it, usually with a bowl of mikan somewhere on top.

Ownership has dropped sharply. TBS’s annual survey of Tokyo-area households found that 93% owned an electric version in 1978 and 30% in 2022 (TBS, 2022).

What Is a Kotatsu?

The name joins the kanji for a torch or fire with the one for a foot warmer. Wiktionary defines it as a knee-high table with an electric foot warmer installed inside, used with a coverlet during winter. In plain terms, a heat source sits under the tabletop, a futon traps what it gives off, and nothing has to heat the whole room.

You’d normally find one in a washitsu, the Japanese-style room, with people seated on the floor around it. Furniture-style versions built for chair seating exist too.

It helps to rule a few things out. It isn’t a heated blanket, since the heater is fixed to the table and the quilt only holds the heat in. Nor is it a room heater. It warms the space under the futon and leaves the room air as it was.

And a quilt thrown over an ordinary low table does nothing without a heat source underneath.

How Does a Kotatsu Work?

Heat from a low-wattage heater unit stays inside the small space the futon seals off. The quilt stops warm air from escaping, so a few hundred watts is enough to warm legs and feet while the rest of the room stays cool.

Heater Unit

Metro’s MSU-501H replacement heater is rated 510 W at 100 V and carries a thermal fuse and a current fuse as safety devices, according to its published specifications.

Yamazen’s ESK-751, a 75 cm square table, ships with a 300 W unit at the same voltage. A dial or hand controller sets the heat level, and the thermal fuse cuts power if the unit overheats.

Tabletop

The tabletop is a plain wooden board, and it is what turns the kotatsu into a place to eat or work.

On most electric models the heater is bolted to the underside of this board. Many tables have a reversible top (KEN JAPAN’s KB-75US is one), so either face can point up.

Kotatsu Futon

A thin futon or rug goes on the floor under the table. The heavy quilt, the kotatsu-buton, drapes over the frame and hangs past the edges, and the tabletop is set on top of it.

Use a quilt made for the purpose. Regular throws are not designed to tolerate the heat under the table.

Okigotatsu vs Hori-gotatsu and the Heater Types

The portable kind is the okigotatsu, a table with the heater fixed to its frame. Put a table over a pit cut into the floor and you get the hori-gotatsu, where people sit with their legs hanging down.

Type Installation Heat source Portability
Okigotatsu Table set on the floor Electric heater under the top Moves between rooms
Hori-gotatsu Table over a pit in the floor Electric heater (charcoal in older houses) Fixed
Hibachi okigotatsu (historical) Frame over a brazier Charcoal Movable, with open-fire risk

Okigotatsu and Hori-gotatsu

Okigotatsu, the portable kotatsu that stands on the floor

Okigotatsu is the more common of the two, according to Expats Guide Japan. It stands on bare flooring or on tatami mats, and it works in any room with an outlet.

A hori-gotatsu is a build decision rather than a purchase. Japan Unknown notes that forms needing a permanent floor opening declined as the okigotatsu spread, though electric heaters now sit in the pit version too.

Electric Heater Types

No heater type wins on every count.

Quartz tube is the classic element and gives off far-infrared heat. Japan Living Guide says it costs less to run than halogen but warms up more slowly. Halogen is the quickest to warm, and Akada’s 120 x 80 cm table uses a 600 W halogen unit. Carbon flat heaters are slim, which leaves more room for your legs, but they run cooler and slower than the other two.

Retailer guides contradict each other on quartz warm-up, with some calling it slow and others quoting a few minutes. The manufacturer’s spec sheet settles it better than any general claim.

Together with the 300 W and 510 W units from the previous section, household heaters run from 300 to 600 W.

Where Did the Kotatsu Come From?

The kotatsu developed from the irori, a sunken hearth at the center of the home, during the Muromachi period (1336 to 1573). People placed a platform over the hearth and covered it with clothing to keep the heat close.

The irori sat in the middle of the main room in traditional Japanese homes and handled cooking, light and warmth at once. The kotatsu turned the warmth part into a piece of furniture.

Where the sources agree, the order runs like this. A frame and cloth over the irori came first, in Muromachi. In the Edo period (1603 to 1868) the hibachi, a charcoal brazier, replaced the irori as the heat source, and the portable okigotatsu appeared. The first electric units arrived in the late Taisho and early Showa years (1920s), and after the war, table-style electric kotatsu reached ordinary homes.

The sources don’t agree on everything, though.

Age first. Okawa Kagu says the term dates back over 500 years, while Tokyo Weekender says around 700. Both fit the Muromachi window, which began about 690 years before 2026 and ended about 450 years before it.

Then the hori-gotatsu. Apartment Therapy calls it the first form, in Muromachi, and Tokyo Weekender dates it to the Edo period. The Japan Weather Association’s tenki.jp (2018) and Weathernews (2023) both credit the sit-down pit version to the Meiji era.

Ikehiko and the culture site wanosuteki.jp go further and say the Meiji pit was the idea of British potter Bernard Leach, who found sitting on his heels hard.

Electric units follow the same pattern. Matsushita Electric (now Panasonic) launched its National electric kotatsu in 1929 with temperature control and a safety device, and sold 45,000 units in year one and 80,000 in year two, per Ikehiko.

Tokyo Weekender places electric kotatsu in the 1950s, but that decade marks mass adoption, not the first unit. Toshiba’s 1957 table-style electric yagura kotatsu, with the heater on the underside of the top board, was the hit that spread it to ordinary homes (Weathernews, 2023).

Weathernews puts peak annual sales at 3.68 million units in 1974, while Mikado Denso dates the peak to 1973. Toshiba stopped making kotatsu in 2000.

Electric models also removed the open fire and carbon monoxide risk that came with charcoal, which wanosuteki.jp names as their main advantage. Airtight housing, air conditioners and kerosene fan heaters then pulled sales down, according to umemo.info.

The Kotatsu in Japanese Winter Life

Hori-gotatsu sunk into the floor with the futon draped over it

In winter a Japanese household tends to end up around one warm table, and meals, television, homework and conversation all move there. Japan Living Guide compares it to a fireplace as a family gathering spot.

A bowl of mikan, the Japanese mandarin, on the tabletop is the standard winter image. Expats Guide Japan calls it a nostalgic seasonal symbol, fubutsushi in Japanese.

Seating stays low. Most people sit on zabuton floor cushions laid on the tatami around the table.

Anyone who wants back support uses a legless zaisu chair, which slides the legs under the quilt like a cushion would.

Jeepe’s kotatsu guide lists a few basics of etiquette. Take off shoes or slippers before getting in, slide your legs in without lifting the futon high, and watch the feet of whoever sits opposite you. Shift position now and then, and keep the futon clean.

Some households mark the start of the season with kotatsu-biraki, bringing the table out on a day of the boar in the month of the boar. Tenki.jp describes the custom, which follows the old zodiac calendar.

How Much Does a Kotatsu Cost to Run Compared With Other Heaters?

A kotatsu costs about 2.5 to 18.6 yen per hour in Japan, depending on whether you price its rated wattage or the power it draws once the thermostat starts cycling. Published estimates for real use sit at the low end.

Both figures use the 31 yen per kWh guide price set by the appliance industry’s fair trade council (EFTC), revised on 22 July 2022 and tax included. Your own tariff will differ, so swap in your rate.

Nitori’s Flot G 105 VNA has a 510 W heater, which prices at 15.8 yen per hour if it ran flat out. Its published estimate is 2.5 yen on low and 5.3 yen on high, as reported by Machi-ene.

At rated power, the comparison looks like this (Docomo Denki, priced at 31 yen per kWh):

Heater Rated power Cost per hour Area warmed
Kotatsu 300 to 600 W 9.3 to 18.6 yen Lower body
Hot carpet (2 tatami) 500 W 15.5 yen Floor area
Air conditioner (8 to 12 tatami) 800 to 900 W 24.8 to 27.9 yen Whole room
Oil-filled heater 600 to 1,500 W 18.6 to 46.5 yen Whole room

Take a 300 W kotatsu running 4 hours at full power. That draws 1.2 kWh, or 37.2 yen. A 1,500 W oil-filled heater over the same 4 hours draws 6 kWh, or 186 yen.

Heater type barely moves the bill, and sources disagree on which is cheapest. Docomo Denki’s table puts carbon highest, while ENECHANGE’s puts it lowest.

On the plus side, a kotatsu has the lowest hourly cost of the heaters compared above, and the heat goes only where people sit. It doubles as a dining or work table too.

Against that, it warms the lower body only, so the room stays cold. Floor seating or a high-type table is a requirement, and long use carries a low-temperature burn risk.

The kotatsu wins on cost per hour and loses on coverage. Machi-ene notes that pairing it with an air conditioner may let you lower both settings.

Is It Safe to Sleep Under a Kotatsu?

Not for long. A short nap is fine, per Jeepe’s kotatsu guide, but a full night under the quilt keeps the legs near the heater for hours, which is how low-temperature burns and dehydration start.

NITE and the Consumer Affairs Agency have both put numbers on the risk.

  • 179 kotatsu accidents reached NITE in the five fiscal years 2005 to 2009 (NITE, 2010)
  • 22 were fatal, with 27 deaths in total, and 19 of those 27 victims (70%) were aged 60 or over
  • 85 of the accidents were fires that spread through at least one room
  • Skin at 44 degrees C for 3 to 4 hours can suffer a low-temperature burn (Consumer Affairs Agency, 2015)

Burns and Dehydration

One case in the Consumer Affairs Agency’s 2015 notice involved a person who fell asleep in a kotatsu and woke to bleeding toes. Two toes were amputated and a third needed a skin graft.

Exposure times differ by source. The Agency and NITE put 44 degrees C at 3 to 4 hours, while a JA hospital page puts it at about 6 hours.

NITE’s January 2025 mail magazine adds that pressure on the skin shortens the time, and that burns below 44 degrees C are possible.

The JA hospital page flags infants and elderly people as higher risk, along with anyone asleep after alcohol or sleeping pills. People with diabetic nerve damage are on the list too, since they feel heat late.

Dehydration runs alongside. Tokyo Apartment Inc. points out that body temperature rises under a kotatsu while winter air is already dry, so drink water regularly.

A long-standing Japanese saying warns that sleeping in a kotatsu gives you a cold.

Fire Risk

Misuse drives most of it. NITE classed 59 of the 179 accidents (33%) as not caused by the product, and Nikkei xTECH’s report on the findings adds that misuse and unidentified causes dominate.

Tokyo Apartment Inc. says drying clothes or towels on the kotatsu has caused burns and fatal fires in Japan. News on Japan points to cushions and clothing left stuffed under the quilt. Furniture pressing on the power cord is another cause, as is a heater unit clogged with dust. Leaving the switch live while nobody sits there rounds out the list.

When buying a Japan-market unit, look for the PSE mark. The diamond mark means third-party assessment for higher-risk products, and the round mark covers the rest (JQA).

Charcoal Models

Charcoal kotatsu sit in a different risk class.

NITE has issued a notice about briquette (mamedan) kotatsu fires, citing incidents with deaths and whole-house losses. Its examples trace fires to worn insulating wadding in the firebox and to overloading the briquettes.

Charcoal also gives off carbon monoxide, so any room where one burns needs ventilation.

How to Choose a Kotatsu Size and Use One Outside Japan

Size follows headcount and voltage follows the outlet. Allow about 60 cm of tabletop width per adult, and in North America buy a 120 V model or put a correctly rated step-down transformer between a 100 V Japanese unit and the wall.

  1. Count the adults who will sit at it and allow about 60 cm of tabletop width each (Kakaku.com).
  2. Pick a shape and size: 75 to 80 cm square for one or two people, about 105 x 75 cm for two or three, about 120 x 80 cm for three or four, per the sizing charts of Japanese shops such as Qualial and Oyasumi.
  3. Match the kotatsu futon to the tabletop shape, because Ikehiko warns that a quilt that is too small leaves gaps and loses heat.
  4. Match the voltage to your outlet, as covered below.
  5. Plan the seating and leave at least 25 cm between chair and kotatsu so feet clear the heater (Kotatsu Tokyo).

For a Japanese unit in North America, the cleaner route is a 120 V model, and BJDesign sells tables with 120 V plugs in 29 x 29 in and 47 x 31 in sizes.

The other route is a 100 V unit with a transformer, but the converter has to outrate the heater. VCT’s VT-500J lists 500 W as its maximum including surge, which falls short of a 510 W heater. Sellers also advise a converter when a 100 V unit goes on a 120 V outlet, though some Amazon owners report it runs fine on a lower setting.

The arithmetic favors the sellers. Power through a resistive element rises with the square of voltage, so 120 V on a 100 V element is up to 1.44 times the rated draw on paper.

Europe is a bigger gap, with 230 V mains against 100 V. Shoran Japan states that one of its 100 V tables cannot ship to Europe because of CE marking requirements at customs.

Floor seating is the sticking point for many Western buyers. KotatsuTable.net suggests floor-level sofas or a wooden zaisu, and Kotatsu Tokyo says a large futon lets you stretch your legs when you sit on a sofa.

Andreea Dima
Latest posts by Andreea Dima (see all)