Originally posted by Rhapsody:

The thing at 3:50 is a smelter or blast furnace inside a house, and a fire hazard.

correct all thats done is they have progressed to blast furnace or smelter and raised it up in side the house so it sticks out the top... can be done just as easy with stone floors without using iron... But to put a chimney over a hearth to cook on .. not gunna work , this just aesthetically looks like a chimney from out side and provides a comfort bonus. but no cooking.