Have a question...in calculating smoke chamber for a reverse flow. Do you calculate the area of the raw tank or the area after the baffle has been put in. It can have an effect on the size of the fire box and all openings I've found a chamber(semi fuel tank) 48 x 24 Bigger than the patio size I wanted but oh well Because it is so long, I'd like to put as small a fire box as possible Have a 16 x 34 air compressor tank but if I can get away with it, I'd like to go smaller. Hence the reason for my original question. So far..it's been fun. Learning welding as I go along Welds aren't pretty but will hold. Getting better