How to Vent a Commercial Coffee Roaster
Venting a commercial coffee roaster can be surprisingly difficult. Most of the venting systems people are familiar with are negative pressure systems. This means that heated air rises so that the pressure inside the pipe is actually less than the pressure in the room. Commercial coffee roasters are exactly the opposite. Combustion gases, steam, smoke, condensed coffee oils are power vented via an exhaust fan so that the exhaust in the pipe is higher than normal atmosphere. This is call a Class III positive pressure system.
Attempting to use a negative pressure venting system like Class B or L or A venting, or stovepipe or pretty much anything you find at the local hardware store is doomed to fail unless each individual joint is sealed with caulk or tape.
Problems then multiply because cleaning is more difficult and less frequent once the joints are sealed. Coffee dust, condensed coffee oil and chaff accumulation can cause fires in the chaff collector and venting. If the worst happens, that light and inexpensive venting is not what you want standing between you and immolation.
Where local regulations permit, we prefer Nordfab QF venting because it meets positive pressure requirements and easily disassembles without tools. This makes maintenance easier, fires less likely, installation cleaner and safer.