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The 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.
NOTE: Where the exhaust duct passes through a wall, ceiling, or roof made of combustible materials,
the opening must be 2-inches (5.08 cm) larger (all the way around) than the duct. The duct
must be centered within this duct.
a. Outside Duct Work Protection
1) To protect the outside end of horizontal duct work from the weather, a 90° elbow bent downward
should be installed where the exhaust exits the building. If the exhaust duct work travels vertically
up through the roof, it should be protected from the weather by using a 180° turn to point the
opening downward. In either case, allow at least twice the diameter of the duct between the duct
opening and the nearest obstruction.
IMPORTANT: DO NOT use screens or caps on the outside of opening of exhaust duct work.