Hello all, New to the forum. Building a Reverse Flow using a 1946 30 gallon air compressor tank. I am building this thing mostly out of scrap I have laying around. With that plan in mind, I have 3' or so of 3" stainless automotive exhaust pipe left over. Can I use it for the chimney? Does the chimney need to be a certain wall thickness? I ran my numbers through the Feldon calculator and it called out 19.14" for 3" pipe. Thanks all. Ben BTW.... Great forum you guys have here. A lot of knowledge here.