Instead of air heaters, Koreans have heated floors. Called ondol (warm stone), the heat is passed in pipes under the floor. This heating system goes back to the Koguryo (or Goguryeo) Dynasty (37–668 BC). In South Korea, more than 90% of the houses have ondol, and people eat, sleep, and watch TV on the warm floor.

Source: https://www.factretriever.com/south-korea-facts