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a. Outside Ductwork Protection
1) To protect the outside end of the horizontal ductwork from the weather, a 90° 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 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, louvers, or caps on the outside opening of the exhaust
ductwork.
2. Single Dryer Venting
a. Horizontal Venting
When possible, it is suggested to provide a separate exhaust duct for each dryer. The exhaust duct
should be laid out in such a way that the ductwork travels as directly as possible to the outdoors with as
few turns as possible. It is suggested that the use of 90° turns in ducting be avoided; use 30° or 45°
angles instead. The shape of the exhaust ductwork is not critical so long as the minimum cross section
area is provided.
IMPORTANT: Minimum duct size for a gas, electric, or steam dryer is 14-inches (35.56 cm) for a
round duct or 12-1/2” by 12-1/2” (31.75 cm by 31.75 cm) for a square duct.
DUCT SIZE MUST NOT BE REDUCED ANYWHERE DOWNSTREAM
OF THE DRYER.
IMPORTANT: Exhaust back pressure measured by a manometer at the dryer exhaust duct area must
be no less than 0 and must not exceed 0.3 inches (0.74 mb) of water column
(W.C.).
IMPORTANT: It is recommended that exhaust or booster fans not be used in the exhaust ductwork
system.