Beds heated by fire: the kang, and everyone who copied the idea

It looks like a fire hazard, but it is called a kang. In northern China, a raised platform of brick or clay is hollow inside. Hot smoke from a stove, often the same one used for cooking, travels through channels under the sleeping surface and exits through a chimney. The mass of brick soaks up the heat and releases it slowly. A well-built kang can hold roughly 40°C overnight, even after the fire has died down.

**Not an open fire.** The flames are never under the sleeper. Only the hot gases pass beneath the platform. The kang heats the bed area, not the whole room, so people wrap up in thick bedding while the air around them stays cold.

**Very old.** Archaeological sites near Shenyang show heated bed floors as early as about 7,200 years ago, and a single-flue heated platform was found in 1st-century remains in Heilongjiang. These dates come from secondary summaries of Chinese archaeology; treat the earliest one as indicative.

**The same idea, different countries.** - **Korea, ondol:** the smoke runs under the entire floor, so the whole room is heated, not just the bed. Ondol was common in Korean homes until the 1960s. A 2023 architectural history paper argues Frank Lloyd Wright took the floor-heating idea for his Usonian houses from the Korean ondol. - **Rome, hypocaust:** hot air under raised floors, used mainly in baths and villas. It faded in western Europe after the Roman Empire declined. - **Spain, gloria:** a descendant of the hypocaust used in Castile until modern heating arrived. Once the wood burned to ashes, the air intake was closed to trap the heat. - **Russia and Japan:** large masonry stoves where people slept on top, and the electric or charcoal-heated kotatsu. Researchers treat these as related but distinct systems, not copies of one another. We make no claim about who invented what first.

**The catch.** Smoke leaks can cause carbon monoxide poisoning, so ventilation and sealed flues were critical. The risk was well known to the families who used them.