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ALL duct work should be smooth inside with no projections from sheet metal screws or other obstructions
which will collect lint. When adding ducts, the duct to be added should overlap the duct to which it is to be
connected. ALL duct work joints must be taped to prevent moisture and lint from escaping into the building.
Inspection doors should be installed at strategic points in the exhaust duct work for periodic inspection and
clean-out of lint from the duct work.
IMPORTANT: Exhaust back pressure measured by a manometer in the exhaust duct should
not exceed 0.3 inches of water column.
IMPORTANT: Minimum duct work diameter is 14 inches.
NOTE: Where the exhaust duct work passes through a wall, ceiling or roof made of combustible materials,
the opening must be 2 inches larger (all the way around) than the duct. The duct must be
centered within this opening.
Outside Duct Work Protection
1. To protect the outside end of horizontal duct work from the weather, a 90º elbow bent downward
should be installed where the exhaust exits the building. If the duct work travels vertically up through the
roof, it should be protected from the weather by using a 180º turn to point the opening downward. In either
case, allow at least twice the diameter of the duct opening and the nearest obstruction.
IMPORTANT: DO NOT use screens or caps on the outside of opening of exhaust duct work.