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a. Outside Ductwork Protection
1) To protect the outside end of horizontal ductwork from the weather, a 90º elbow bent downward
should be installed where the exhaust exits the building. If the exhaust ductwork 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 between the duct
opening and nearest obstruction.
IMPORTANT: DO NOT use screens, louvers, or caps on the outside opening of the exhaust
ductwork.
NOTE: Exhaust back pressure measured by a manometer at the dryer exhaust duct area must
not exceed 0.3 inches (0.74 mb) of water column (W.C.).
NOTE: When the exhaust ductwork passes through a wall, ceiling, or roof made of combustible
materials, the opening must be 2-inches (5.08 cm) larger than the duct (all the way around).
The duct must be centered within this opening.