To find out about ondol, the home heating system that’s commonly used in Korea, you can read this article from the Korea Times.
The traditional Korean fireplace, however, is “invisible” because it is an under-the-floor structure, hidden from the surface. Traditionally, Koreans used this underfloor-heating device, called “ondol,” to get through the long and cold winter.
The history of ondol goes back to the Neolithic Age, according to Kim June-bong, a professor of architecture at the Beijing University of Technology.
In the Goguryeo period (37 BC_ 668), an “L”-shaped ondol was common that provided partial heating to the room floor. Then, it evolved into a full-room ondol (tong ondol) in the Goryeo period (918 – 1392). By the end of Goryeo, the ondol structure spread to the entire Korean peninsula.
Meanwhile, ondol has been undergoing its own metamorphosis to fit the new demands of time. Ondol was originally fired by wood, but modern homes and apartments are built with heating pipes embedded in the floors. Heated water circulating through the pipes, warmed by a gas or an oiler, has replaced heated air.
Professor Kim claims not to be nationalistic and yet:
And the first step in that direction [promoting ondol internationally] is for the government to preserve and promote the ondol culture, while it should also engage in an effort to correct some misinformation about ondol ― for example, as something related to the Roman hypocaust, which is an ancient system of central heating.
While ondol and the Roman’s hypocaust are not related, in the sense that they were invented independently, it is misleading to claim that they are completely different.
And here is an article about the oldest ondol system discovered so far:
What are believed to be the world’s oldest underfloor stone-lined-channel heating systems have been discovered in Alaska’s Aleutian Islands in the U.S. The heating systems are remarkably similar to ondol, the traditional Korean indoor heating system.
Richard Knecht, from the University of Alaska, and Song Ki-ho, of the department of Korean history at Seoul National University, reached some interesting conclusions:
As the ondol of North Okjeo and Amaknak are more than 5,000 kilometers apart, Knecht and Song agree that the two systems seem to have been developed independently.
This theory is backed up by the fact ondol have not been found in areas between the two locations, such as Ostrov, Sakhalin or the Kamchatka Peninsula, and because the Amanak ondol are significantly older than those of the Russian Maritime Province.