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Ondol (Underfloor Heating)

Ondol (Hangul: 온돌; Hanja: 溫突), also called gudeul (Hangul: 구들), in Korean traditional architecture, is underfloor heating that uses direct heat transfer from wood smoke to heat the underside of a thick masonryfloor. 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 a firebox or stove (agungi; 아궁이) accessible from an adjoining (typically kitchen or master bedroom) room, a raised masonry floor underlain by horizontal smoke passages, and a vertical, freestanding chimney on the opposite exterior providing a draft. The heated floor, supported by stone piers or baffles to distribute the smoke, is covered by stone slabs, clay and an impervious layer such as oiled paper.

Modern Floor Heating : Thanks to 'Mr. Frank Lloyd Light', the modern architect of the U.S.A., the Korean Ondol is known to overseas countries. He lodged at a Korean house during the travel in Japan, and being fascinated by the floor heating he applied it to his work in U.S.A., which might be the first case that the Ondol was introduced to overseas countries. 

He described on the Ondol in his auto bibliography as follows.

“Korean room is the best heating method ever invented by the mankind. To keep the feet warm is the most idealistic heating.”

Why is the underfloor heating good?

○ Comparison of Floor Heating and Convection Heating through the Experiment


If seen through the 6 indexes of indoors heat environment of the 6 values of indoor temperature, humidity, air flow speed etc., the air flow speed is minute, and the temperature difference of the upper part and lower part is also small. Due to this, the floor heating is pleasant as a uniform heat exchange is available from the head to the end of feet. 


Upper Part

It shows the temperature changes of the floor heating and convection heating  in the air. 

It can be seen that the temperature evenly rises from the floor in case of the floor heating, while it rises from the surrounding of the heater only and the heat goes up to the upper part in case of  convection heating.


Lower Part 

The temperatures of body were measured at each heating room after 10 minutes.

It can be found that it is evenly warm from the head to the feet in case of the floor heating, while it is warm only for the head and it becomes colder for the lower part in case of the convection heating.

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