I used a few pieces of 12" galvanized pipe, and an elbow, which followed me home from work. these formed the horizontal portion. Continued the main vertical stack with 12" duct made from 2 pieces of 6" duct snapped together. this was a much lighter guage metal, but it should last a while. at the forge, the galvanized part that's over the fire is a removable hood, not part of the horizontal pipe, which stops behind the big rusty plate. (the grey disk thingie behind the vertical pipe, on the exterior wall, is an exhaust fan discharge, which I always run when working, especially in the summer time)