Kudul (heated floor in Korean) is a national intangible cultural heritage of the DPRK.
The word was derived from kuundol, which means heated stone. It was also once called ondol which means warm stone.
In the course of using a brazier to keep themselves warm, the Korean ancestors understood that stones around the brazier preserved heat for a long time. Kudul was a facility of heating larger numbers of stones gradually by using this simple principle.
A historical document on the kingdom of Koguryo in the period of Three Kingdoms recorded that Koguryo people used to build kudul and made a fire under it to keep them warm in winter. Drawings of facilities can be seen on the walls of the Mausoleum of King Kogugwon and the tomb murals in Yaksu-ri.
During the period of Koryo (918-1392), facilities began to develop into two forms–ones with a floor with ducts under it and ones with a stone-covered floor.
In the feudal Joson dynasty (1392-1910), an all-floor-heating system pervaded the whole country.
The heated-floor system represents the creative wisdom and efforts of the Korean people to make rational use of heat and reflects their early clean and civilized living manners.
The system makes it possible to control the temperature in a room evenly, keep the room warm for a long time without using any other fuel and prevent humidity and cold from the floor. For such advantages, it is widely used everywhere in the country.
Today, the Korean people not only set up the system in one-story and multi-story houses but also introduce other systems of heating the floor by means of hot water and electricity, thus preserving the traditional living customs of the nation.