One day in October 1954, President Kim Il Sung visited multi-storeyed apartment houses for workers under the construction on the bank of the Taedong River.

   After acquainting himself with the interior structures of the houses, he asked the construction engineers if it was possible to introduce ondol (underfloor heating system) favoured by the Koreans. 

   They could not answer promptly as there would be many knotty problems to this end.

   Noting that the Koreans were not accustomed to beds as they have lived in the underfloor-heated rooms since olden times, Kim Il Sung asked them to study the ways to introducing the system to meet their living customs. 

   One day in October 1961, he examined the designs of new dwelling houses. Noting that the Korean people preferred the underfloor heating system, he explained a new method of introducing it in such a way of putting pipes under the floor.

   It was a new discovery which could be made only by Kim Il Sung who attached great importance to the folklore tradition of the Korean people.

   According to his instruction, a hot-water floor-heating system began to be widely introduced into all the multi-storeyed houses.