A kotatsu is a type of home heater where a low table is placed over an electric heater on the floor and is covered with a futon (a quilt or heavy blanket) that traps in the heat. Your entire lower body will be warmed by placing your legs underneath the blanket. A sunken kotatsu (hori-gotatsu) is another style of the kotatsu that has a recessed floor with an open pit where your heater of choice is placed, and the kotatsu is placed on top of that. Being able to sit in a chair and dangle your feet into the warmth below is one of the sunken kotatsu's unique characteristics.

Source: Taito Ryokan, Asakusa: Vintage 1950s Japan

Origin of the Kotatsu

In the past, people used to warm their chilled bodies with a sunken hearth (known as irori in Japanese. The irori refers to the square they would cut out of the floor and light a fire in). Unfortunately the sunken hearth was not able to warm up the entire body, and so around the end of the 14th century and the early 15th century, they devised a wooden square-frame (called yagura)to place over the dying embers of the fire and placed a quilt on top of that to keep the heat from escaping. This is thought to be the origin of the kotatsu.

Source: IRORI Nihonbashi Hostel And Kitchen – The Guesthouse With An Irori

In the 17th century they made the heater transportable by putting the hot charcoal in earthenware or china. This transportable home heater was known as an anka (a type of foot or bed warmer), and is the predecessor of the modern kotatsu.

Once the 1950's hit, the kotatsu switched to electricity as its heat source, as opposed to using charcoal and briquette. The electric kotatsu quickly spread through Japanese households in no time.

Source: Enjoy Old-Style Japan at Gonpachi G-Zone Ginza

Lifestyle Change and the Kotatsu

Until around the 1980's, every household had an electric kotatsu and going under the kotatsu's quilt to eat mandarin oranges became a customary winter scene. The influence of Western styles on modern Japan has made it commonplace for households to use stylish low tables and kotatsu outside of the winter months as well.

However, households without a kotatsu have increased in number due to the spread of other types of home heaters in recent years. But, Japanese-style restaurants and izakayas often have seats surrounding a sunken kotatsu, allowing the majority of Japanese to enjoy a kotatsu-like experience there.