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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. Maximum proportional duct work runs
cannot exceed twenty
(20) feet more than the original limitations of twenty (20) feet with two (2) elbows.
When the duct work approaches the maximum limits as noted in this manual, a
professional HVAC firm should be consulted for proper venting information.
IMPORTANT: Exhaust back pressure measured by a manometer at each dryer exhaust duct area
should not exceed 0.3 inches of water column.
The duct 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 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.
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
nearest obstruction.
IMPORTANT: DO NOT use screens, louvers, or caps on the outside of opening of exhaust duct work.