A is a low, wooden table frame covered by a futon, or heavy blanket, upon which a table top sits. Underneath is a heat source, formerly a charcoal brazier but now electric, often built into the table itself. Kotatsu are used almost exclusively in Japan, although similar devices for the same purpose of heating are used elsewhere, e.g. the Spanish brasero or Iranian korsi.
History
The history of the kotatsu begins in the Muromachi period or Ashikaga shogunate during the fourteenth century. Its origins begin with the Japanese cooking hearth, known as the irori. Charcoal was the primary method of cooking and heating in the traditional Japanese household and was used to heat the irori. By the fourteenth century in Japan, a seating platform was introduced to the irori and its cooking function became separated from its seating function. On top of the wooden platform a quilt was placed, known as an oki that trapped and localized the heat of the charcoal burner. This early ancestor to the modern kotatsu was called a hori-gotatsu. The word hori-gotatsu () is derived from the kanji (hori) meaning ditch, digging, (ko) meaning torch or fire, and (tatsu) meaning foot warmer.
The formation of the hori-gotatsu was slightly changed in the Edo period during the seventeenth century. These changes consisted of the floor around the irori being dug-out into the ground in a square shape. The wooden platform was placed around this, making a hearth. Then the blanket was placed on top of the platform again, where one could sit with legs underneath to stay warm.
The moveable kotatsu was created later, originating from the concept of hori-gotatsu. This kotatsu came about with the popular use of tatami matting in Japanese homes. Instead of placing the charcoals in the irori, they were placed in an earthen pot which was placed on the tatami making the kotatsu transportable. This more modern style kotatsu is known as the oki-gotatsu. The word oki-gotatsu () is derived from the kanji (oki) meaning placement, meaning torch or fire, and meaning foot warmer.
In the middle of the twentieth-century charcoal was replaced with electricity as a heating source. Instead of having the moveable earthen pot of charcoals beneath the kotatsu, it was possible to attach an electric heating fixture directly to the frame of the kotatsu. By 1997, the majority (approximately two-thirds) of Japanese homes had the modern irori and 81 percent had a kotatsu, though they are warmed using electricity instead of glowing coals or charcoal. Thus, the kotatsu became completely mobile with electricity and became a common feature of Japanese homes during winter.
Types
There are two kinds of kotatsu used in Japan today, differing in the configuration and the type of heating: Electric: The modern style of kotatsu, , consists of a table with an electric heater attached to the underside of the table. This evolved from a clay pot with hot coals placed under a table. The kotatsu usually is set on a thin futon, like a throw rug. A second, thicker blanket is placed over the kotatsu table, above which the tabletop is placed. The electric heater attached to the underside of the table heats the space under the comforter. Charcoal: The more traditional type is a table placed over a recessed floor, . The pit is cut into the floor and is about 40 centimeters deep. A charcoal heater is placed somewhere in the pit's floor, walls, or, as in the modern-style kotatsu, attached to the table-frame. There are pit-type kotatsu with an electric heater too.
Use
In the twenty-first century, the kotatsu typically consists of the electric heater attached to the frame, which is no longer limited to wood, but may be made of plastic or other materials. Generally, a blanket (or shitagake) is draped over the frame and heater and under the table-top. This first blanket is covered by a second heavier blanket, known as a (). A person sits on the floor or on zabuton cushions with their legs under the table and the blanket draped over the lower body. The kotatsu was designed when people most commonly wore traditional Japanese style clothes, where the heat would enter through the bottom of the robes and rise to exit around the neck, thus heating the entire body.