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b. Vertical 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 with a vertical run and not more
than three (3) elbows (including dryer connection and outside outlets) is 16-inches
(40.64 cm) for a round duct or 14-1/2" by 14-1/2" (36.83 cm by 36.83 cm) for a
square duct. Duct size must not be reduced anywhere downstream of dryer.
IMPORTANT: Exhaust back pressure measured by a manometer at each basket (tumbler) exhaust
duct area must be no less than 0 and must not exceed 0.3 inches (0.74 mb) of water
column (W.C.).
It is suggested that the ductwork from each dryer not exceed 20 feet (6.1 meters) with no more than
three (3) elbows for a vertical duct (including the dryer connection and outside outlets). If the ductwork
exceeds 20 feet (6.1 meters), or has numerous elbows, the cross-sectional area of the ductwork must
be increased in proportion to the length and number of elbows in it. In calculating ductwork size, the
cross-sectional area of a square or rectangular duct must be increased by twenty percent (20%) for
each additional 20 feet (6.1 meters). The diameter of a round duct should be increased ten percent
(10%) for each additional 20 feet (6.1 meters). Each 16-inch (40.64 cm) 90º elbow is equivalent to 36
feet (11 meters) and each 18-inch (45.72 cm) 90º elbow is equivalent to 41 feet (12.5 meters).
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