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IMPORTANT: For extended duct work runs, the cross section area of the duct work can only be
increased to an extent. When the duct work approaches the maximum limits
noted in this manual, a professional heating venting air conditioning (HVAC)
firm should be consulted for proper venting information.
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.
NOTE: Where the exhaust duct work 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 opening.
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 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.