Thanks,
This is good info. and very valuable, but I can't make an opening in the building for a stack. I can run a duct to a window and out to a stack (may even look at making a cyclone to knock the ash down). I plan on opening the window and putting an insert in the window to pass the duct through. (I am watching space to combustible material.) This would make the need to be forced air. No A/C or heat so I know what I have for outside temp will be pretty much be the same due to fresh air draw. I have two other windows, a man door and an overhead door to crack open to allow air in. I am looking to see if someone knows the magic cfm to draw out the exhaust and not make the need to put a warning about small children and animals getting to close to the hood. :D