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b. Vertical Venting
Where 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 duct work 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 duct work
is not critical so long as the minimum cross section area is
provided.
IMPORTANT: Minimum duct size for a gas dryer and 60 Kw or 72 Kw electric 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. The minimum duct size for a steam dryer or 80 Kw
electric dryer is 18-inches (45.72 cm) for a round duct or 14-1/2" x 14-1/2"
(36.83 cm by 36.83 cm) for a square duct. Duct size must not be reduced any-
where down stream of dryer.
IMPORTANT: Exhaust back pressure measured by a manometer at each basket (tumbler) exhaust
duct area should not exceed 0.3 inches of water column (0.74 millibars).
It is suggested that the duct work 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 duct work
exceeds 20 feet (6.1 meters), or has numerous elbows, the cross-sectional area of the duct work must be
increased in proportion to the length and number of elbows in it. In calculating duct size, the cross-
sectional area of 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 centimeters) 90º elbow is equivalent to 36 feet (11 meters) and each
18-inch (45.72 centimeters) 90º elbow is equivalent to 41 feet (12.5 meters).