I've heard they even name babies due to the ancient traditions: spose a bit like Jackson being the son of Jack but with more suggestive meaning.
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Those fire places are called rocket mass heaters or rocket mass stoves. The guy that own the permies website, Paul, has a bunch of videos out about building them and how to make them very efficient.
https://permies.com/forums
https://www.youtube.com/watch?v=4usXIAoy9us