It, originated from bonfire, had a hypocaust flue at the start and then developed into a heating system with a fire hole and several flues.

Later, a kitchen fire entrance was installed between fire hole and flues to elevate thermal efficiency and a channel was made between flues and chimney to block smoke and cold air.

Kudul, which is simple in structure, keeps warmth long and helps promote blood circulation, have a good sleep and cure diseases.

Kudul has drawn public interest in some other countries, too.

Hot-water and electricity heating systems of floor based on hypocaust flues were developed in Germany and vocabularies "kudul" and "ondol" are used as commercial terms and found in dictionaries in some countries.