LOL, after many tries at it, I've found that I'm no good at reinventing the wheel. I never come up with anything better, and I just waste alot of time and money if I try, which is why I'm using the calculator. But because I'm a gearhead, I can't help but think of it like an engine; when you're designing an exhaust system, you determine the diameter of the pipes based on the flow rate, and the length is based on the RPM of the engine. I'm probably over-thinking this, and it's probably fine as long as you have a chimney of a reasonable size (unlike my purposefully ridiculous copper tubing example), but I'm prone to over-thinking things. Considering the viscosity and velocity of smoke, water vapor, carbon dioxide, and other smoker exhaust gasses, I think frictional losses should be negligible, but I do like your idea of thermal mass in the chimney.
