Ondol, literally "warm stones," refers to an underfloor heating system unique to Korea. It has its roots in a primitive form of heating based on a hearth and flues dating back to the Bronze Age and the Proto-Three Kingdoms period. Since early examples of ondol can be found across the Korean Peninsula at sites dating to between the third century BCE and the first century CE, it is estimated that the practice of making and using underfloor heating facilities has been transmitted on the Korean Peninsula for more than 2,000 years.

Unlike Western-style indoor fireplaces, the ondol system does not directly emit exhaust through the chimney. The smoke from a firepit first flows through flues made underneath the floor of a room, keeping the room warm for long periods without producing indoor smoke.

As the quintessential element of traditional Korean housing culture, the ondol system informs on how Koreans have traditionally heated their houses. It illustrates their knowledge and use of the natural environment and their everyday lives. Ondol is also an important element in house building, interior design, and furniture design. Ondol rooms have long been established as one of the most important elements in Korean popular culture.

While the unheated wooden-floored spaces within a traditional Korean house is an architectural response to the summer heat, the ondol rooms are preparations for harsh winter weather. Ondol is a unique Korean housing technology clearly distinguished from the underfloor heating systems found in China and Manchuria. Despite great advancements in heating technology and recent radical changes in housing and lifestyles, underfloor heating continues to thrive the present.

Ondol has been designated as National Intangible Cultural Heritage for its sociocultural value as an indispensable element of Korean housing culture and popular culture, and also for its evidential significance to the creativity and wisdom Korean people exerted in their efforts to adapt to the local climate.

* As the ondol system is part of Korean housing customs long shared widely across the nation, no particular holders or holder groups have been recognized for this element.