Today, under-floor heating is done with electrical systems or pipes of hot water worked in a pattern under (you guessed it) the floor of the home.
Since hot air rises, this can provide a more efficient and even heat through out the room.
It is a more “gentle” heat, so most people use smart thermostats, and occasionally pair it with a secondary heat (for cold climates), such as a heat pump.
An Ondal is the historic Korean technology which used the smoke from a fire to do the same thing.
While it may sound immediately dangerous, they were actually careful to cover the under parts of the house with clay and other types of fire-resistant material. As an added benefit, smoke can prevent mold/rot, and deter insects.
This technology dates back to before circa 5000 BC.
Comparatively, this same method is also how bath houses were heated. While the ones in medieval Europe did have a reputation of burning down, some ancient Roman’s had more luck.
Called the “Hypocaust” system, which apparently means “heat from bellow,” and they did just that.
Under floor heating even goes back further than these examples.
It is funny how often “new” technology is often just updated historic ideas.
