Ondol

In modern usage, it refers to any type of underfloor heating, or to a hotel or a sleeping room in Korean (as opposed to Western) style.

The main components of the traditional ondol are an agungi (아궁이; [a.guŋ.i]), an firebox or stove, accessible from an adjoining room (typically kitchen or master bedroom), a raised masonry floor underlain by horizontal smoke passages, and a vertical, freestanding chimney on the opposite exterior wall providing a draft.

A Neolithic Age archaeological site, circa 5000 BC, discovered in Sonbong, Rason, in present-day North Korea, shows a clear vestige of gudeul in the excavated dwelling (움집).

[3] Alternate names include janggaeng (장갱; 長坑), hwagaeng (화갱; 火坑), nandol (난돌; 暖突), and yeondol (연돌; 烟突).

In the Annals of the Joseon Dynasty on May 14, the 17th year of King Taejong's reign (1417), there is a record of making an ondol room for the sick among the students of Seonggyungwan, who were just established at the time.

Traditional ondol systems provide long-lasting warmth after heating but consume significant fuel, requiring large amounts of firewood.

In 1962, to address these issues and improve efficiency, hot-water boilers utilizing the ondol system were developed, reducing both fuel consumption and the risk of poisoning.

[5] The furnace burned mainly rice paddy straws, agricultural crop waste, biomass or any kind of dried firewood.

Unlike modern-day water heaters, the fuel was either sporadically or regularly burned (two to five times a day), depending on frequency of cooking and seasonal weather conditions.

With the traditional ondol heating, the floor closer to the furnace was normally warm enough, and the warmest spots reserved for elders and honored guests.

The famous American architect Frank Lloyd Wright was building a hotel in Japan and was invited to a Japanese family's house.

[7] Instead of ondol-hydronic radiant floor heating, modern-day houses such as high-rise apartments have a modernized version of the ondol system.

[8] North Korea still utilizes the basic traditional design of the Ondol that use mostly coal instead of biomass to survive the harsh winters.

In a traditional Korean house, people usually extinguish the fire before going to sleep at night, since it can stay warm until the morning.