exhaust opening

[lugnutz]

ok I know there are tons of formulas out there for all kinds of things related to smokers, but I'm not sure I have ever seen anything to help figure out how large of an exhaust one needs on the smoker.

Is there a rule of thumb or a formula for figuring this out?

 

[fourthwind]

The length and diameter of the exhaust has to do with how much airflow you get through the smoker.   Hot smoke chases cold smoke therefore the longer and fatter the tube outside the cook chamber the faster the flow.  The formula's that folks have come up with are from experiance through either experiment or sometimes dumb luck.  This is why manufacturers all get different types of results with how meat cooks in their units.  Try the free calculaters that are floating around.  They are a great place to start.  Try this one.  http://www.feldoncentral.com/bbqcalculator.html