Ondol (radiant floor heating)

Replication of Higher Tech

Whether it is post-reset technologies being replicated by surviving humans with materials at hand, or mimicry of offworld tech….the ancient Ondol home heating system in Korea appears to be a remnant of higher technologies.

Link: https://www.antiquealive.com/Blogs/Ondol_Korean_Home_Heating_System.html

Ondol Heating System of ancient Korea