I've been researching build details for a few months since I picked up this water filter tank. It is 304 SS, 30" diameter X 55" long, 3/16" thick. 36944.83 cubic inches. I've built a firebox 27.5 X 24 X 24 from 1/4" steel plate. This is 122% of the recommended size. I have made the 1/2" thick door end 2" bigger all around to have a place to attach the jacketting over the insulation. The opening from the FB to the CC is 155.76 sq in, 27" long 8 3/4" tall with a 1 1/2" grease dam. There are 6 FB intakes 2 1/4 X 3 on the door. I scored some SS 1/8" diamond plate & made the intake sliders from that stock with 3/16" spacers welded to the guides. My chimney will be 6" dia. X 30" long. (24" is recommended). I'll post pics of progress so far. This might take a while to finish, but I'm a detail oriented machinist/welder, and there's no need to rush something that will last a long time.