Hello, great sight and info here. I have been building a reverse flow 500 gallon smoker for my brother. I'm a fabricator/ welder and have experience with metal but not smokers. He came to me a few months ago with a 500 gallon diesel tank and a websight , feldons pit calculator and said use it to get my measurements. Fast forward a few months and I'm 2/3s done with the project and was doing some research on calculating double stack heights cause feldons web doesn't say anything about using 2 stacks. While researching I came across this sight that is saying that feldons websight is flawed for reverseflows and all my measurements are wrong. My question is what effect will this have on the smoker? From what I can tell my intake dampers and hole going to the cooking chamber is a little smaller than it should be. To fix this it will be allot of work I wasn't counting on and really don't want to do it unless the smoker won't work as is. Second question is doing my research I found out 2 six inch pipes have the same carrying capacity as an 8 inch pipe. So I used 8 inch pipe measurements in the calculator and it came to around 3 foot for the 6 inch double stacks. Does that sound about right?Thanks to everyone that puts out the effort on these sights so ppl like me can build our dreams.