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The Korean traditional heating system “ONDOL”

Ondol is a heating system hidden beneath the floor. There are different theories on how old it is, but Chinese records state that during Goguryeo (37 B.C.-A.D. 668), an L-shaped ondol that provided partial heating to the room floor was common. It evolved into a full-room ondol in the Goryeo period (918-1392). By the end of Goryeo, the ondol had spread to the entire Korean Peninsula.

In its traditional form, the ondol utilizes direct heat transferred from wood smoke to the underside of a thick masonry floor. In modern times, the term ondol refers to any type of under-floor heating in Korean housing. "Gudeul," meaning "baked stone," is another name for an ondol.

Old traditional Ondol

The heat of an ondol originally came from wood, but modern homes and apartments are built with hot-water pipes embedded in the floor.

The health benefits of the ondol have long been documented in Korea. A royal record of the Joseon Dynasty (1392-1910) reads, "In June, King Sejong's 12th year, the King ordered the Gyeongsang provincial minister to let the brother Lee stay on the ondol to ward off illness." The ondol is reputed to be especially good for women recovering from childbirth, as well as the elderly.

The traditional Ondol home

Dongil Construction, a Korean construction company, built ondol-based apartments in Kazakhstan, where a significant Korean minority dwells, and in the United Kingdom in 2007. Another Korean company, Woolim, has built 2,566 ondol-equipped apartments in Almaty, Kazakhstan's biggest city. SR Engineering and Construction built 5,372 luxury apartments equipped with ondol in Shenyang, China, and an additional 500ondol-based units in Shanghai.

Source: International Society of Ondol

“ONDOL”- Ancient heating system with modern application

Korea Ondol
In South Korea over 90% of the houses have radiant floor heating. It is called Ondol. The word 'Ondol' means warm stone. It is loved by foreigners as well as by Koreans.
The Korean winters can be chilly, but Koreans of the Choson Dynasty had used a method similar to the Greek and Roman method of heating for centuries.

Traditionally, the source of heat for the ondol was a fireplace. This might be located in the kitchen or on the outside wall of the living room. A kitchen with two or three fireplaces could be surrounded by a matching number of ondol-heated rooms. In an old Korean kitchen, you might find one or two big iron cauldrons on the fireplace. Thus, the fire used for cooking rice or soup was also used to heat the room next to the kitchen!

In general, the kitchen was built two or three feet lower than the room that was being heated. The difference in level made it easy for the smoke and hot air to run under the floor of the elevated room. Smoke running under the floor? Yes, that is the secret of Ondol.

It is said that there was once an ondol room—hundreds of years old—that had incredible thermal efficiency. Because of the design of the room's flue structure, its floor would remain hot for 45 days with just one heating! Warmth could supposedly be felt for 100 days. Unfortunately, that room was destroyed during the Korean War in the early 1950's. In 1982, engineers restored the structure, and tourists can visit its ondol room. The present thermal efficiency is not nearly as good as the original. Still, after one heating, the floor remains warm for ten days in spring and fall, and for three days in winter, even when the temperature is below 14 degrees Fahrenheit.

Ondol has had a great impact on the Korean life-style. For one thing, because the floor is much warmer than the indoor air, people naturally sit on the warm floor rather than on colder chairs. Koreans thus sit, eat, associate, and sleep on the floor. To keep the floor even warmer, they sometimes cover it with a thick bed quilt called ibul. When family members come in from outside, they put their cold legs under the bed quilt to enjoy the comfortable warmth together—a real bonding experience!


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