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When a vent is less than 10 feet high, the vent should be at least as large as the flue collar outlet.b) Vents for draft hoods or flue collars 12 inches in diameter or less should NOT be reduced more than one pipe size.
1 Under no circumstance should gas vent pipe be used for Pellet Vent Pipe, as the inner wall will not stand up to the pellet vent exhaust and pipe will fail very rapidly. 2  Pellet Vent pipe, referred to as L-Vent pipe, can be purchased in 3 inch and 4 inch diameter sizes.