A History and Use of Ondol: Korea’s Traditional Heating System

The ondol, Korea’s traditional underfloor heating system, has not only heated the houses of Korea for thousands of years, it has also, by its very use, shaped and landscaped Korean culture and lifestyle as we witness and experience it to this very day.

The first documented usage of the ondol in Korea’s history has been recorded at an archaeological site in Unggi, Hamgyeongbuk-do, in present-day North Korea. This particular find of the ondolhas been dated as far back as the Bronze Age, circa 1000 B.C.E. The word ondol, meaning “warm stone,” was not always the term used to describe Korea’s traditional underfloor heating system. The term gudeul, which has the same meaning as ondol, has been recorded as the term used colloquially for the modern day ondol in Korea for over two thousand years. Korean historians have recorded the use of ondol in traditional Korean housing, called hanok, as beginning around the end of the 19th century.

Korean homes use the ondol heating system to warm their houses against the bitter cold that resides in Korea during the winter months. The primary difference between today’s heating systems and the original ondol is that today a homeowner can turn his heating system on by a flick of a switch, whereas traditionally the initial heat would have to be generated by lighting a fire. The principles, however, remain the same. The ondol warms a home by transferring heat via under-floor flues, or passages.

This system is unique in its method because it heats a room, or living space, from the outside, as opposed to the typical Western-style heating system, which dictates that the heat should come from inside the room which you are trying to heat. It achieves this, heating a space from outside, through its structure. Each part of its structure provides a specific service; a synergy takes place. Firstly, the heat is created in agungi, a furnace, located in the kitchen, where firewood is burned. The hot air is filtered through horizontal flue passageways that run beneath the room’s floor, connecting the burning furnace to the chimney located at the opposite side of the house. Hot air could then move along the flues, heating the stone,ondol and mud floor.

For this process to succeed, two conflicting requirements had to be met. For the fuel to burn well, its smoke had to pass quickly through the flues and go out of the chimney for any heat to generate under the floors. Flues that were straight and short were best for that purpose. For the heat from the fire to warm the floor, however, the hot air and smoke had to stay in the flues as long as possible. To accomplish this, the flues were made to cover the area under the whole floor, thus preventing the hot air from going out through the chimney too quickly. Thus, the heat would circulate the room as much as possible before exiting through the chimney.

Dealing with a dangerous element such as fire brought its difficulties, such as the potential for the flames coming from a burning furnace to damage the house itself. To overcome such a difficulty, Korea’s ancestors, remarkably, divided the flame from the smoke. The flame would be sent horizontally, against its very nature to rise vertically. This was achieved by having a flue entry located beside the furnace. This was essential as it would not allow the smoke to travel upward, causing the flame to go out too soon. And as the flame would pass through the flue entrance, it would be guided through the network of passages with the smoke.

Traditionally, the ondolwas used primarily for two things, heating a home and cooking. With the latter, when a fire was lighted in the furnace to cook rice for dinner, the heat would not only cook the rice as was expected, but the heat would remain inside the home until the next morning, thus keeping the house warm throughout the night. The smoke, in addition, was put to its maximum usage.

Traditional Korean houses, hanok, due to being constructed with wood primarily, were extremely prone to insects, fungi, bacteria and other worrying hygienic problems attacking a home. However, by lighting a fire, thus causing smoke, the smoke would become a natural sanitizer for the home, killing germs and bacteria as it filtered through the flues. It is incredible to think that the ancestors of Korea, thousands of years ago, were equipped with the knowledge and wisdom to use one of the elements to its full potential, turning a natural danger, fire, into something that both heats and sanitizes a home all at once.

We cannot but admire the ondol system, particularly if you come from the “Western world”, where the individual home relies on oil, a natural resource in diminishing supply but in high demand, to heat homes. The ondol also retains more heat than lighting a fire inside the room you intend to heat. It achieves this as the smoke never enters the room, it remains in the flues.

On a final note, it cannot be stressed enough just how pivotal the ondol system was in landscaping Korean culture and lifestyle. This is evidenced the first time you arrived in Korea and enter a living space or restaurant. The first thing you do is take off your shoes, and more than likely, you sit down on the floor. When you become aware of the ondol heating system, it is logical and makes perfect sense as to why Korean people sit on the floor, for the floor is warmer than the air that is circulating around, thus sitting on a chair would not be as comfortable as sitting on the floor.

The ondol heating system is distinctly Korean. It dates back to the pre-historic age, and as a consequence it is embedded into Korean folklore and tradition. It is remarkable how intuitive and clever Korean ancestors were when creating such a dynamic piece of architecture. It has also given added comfort to one of Korea’s unique and distinctive cultural traits, using the floor as the social space, and not a higher table and chairs, to come together to talk, eat and share in one another’s company. This is, I am sure, something we all treasure about Korea.