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.
In Korea almost every house has this kind of floor heating. It is called Ondol.The word 'Ondol' means warm stone.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.A traditional Ondol floor heating system conducts the flue gases of a fire under the floor of a living space. Horizontal flues passageways for heat and smoke ran beneath the room's floor, connecting the fireplace and the chimney. Hot air from the fire passed through the flues and heated the stone and mud floor. This was not as easy as it sounds. 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 the chimney unhindered. 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. When a happy medium between fast and slow was reached, a room could be kept warm all night with a fire that lasted only a couple of hours.
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!