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Outside Ductwork Protection
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
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° and/or 45° angles instead.
The shape of the exhaust ductwork
is not critical as 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 (minimum 14-inches [35.56 cm]) not exceed 20 feet (6.09
meters) with no more than three (3) elbows (including dryer connections and outside exhaust outlets). If the
ductwork exceeds 20 feet (6.09 meters) or has numerous elbows, the cross section area of the ductwork
must be increased in proportion to the length and number of elbows in it. In calculating duct size, the cross
section area of a square or rectangular duct must be increased by twenty percent (20%) for each additional
20 feet (6.09 meters). The diameter of a round exhaust duct should be increased ten percent (10%) for
each additional 15 feet (4.57 meters). Each 14-inch (35.56 cm) 90° elbow is equivalent to 30 feet (9.14
meters) and each 16-inch (40.64 cm) 90° elbow is equivalent to 36 feet (10.97 meters).