Ondol

Ondol (ON-dol; /ˈɒn.dɒl/,^[1] Korean: 온돌; Hanja: 溫突/溫堗; Korean pronunciation: [on.dol]) or gudeul (구들; Korean pronunciation: [ku.dɯl]) in Korean traditional architecture is underfloor heating that uses direct heat transfer from wood smoke to heat the underside of a thick masonry floor. In modern usage it refers to any type of underfloor heating, or to a hotel or a sleeping room in Korean (as opposed to Western) style.

The main components of the traditional ondol are an agungi (firebox or stove) accessible from an adjoining room (typically kitchen or master bedroom), a raised masonry floor underlain by horizontal smoke passages, and a vertical, freestanding chimney on the opposite exterior wall providing a draft. The heated floor, supported by stone piers or baffles to distribute the smoke, is covered by stone slabs, clay and an impervious layer such as oiled paper.