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MULTIPLE DRYER (COMMON) VENTING
HORIZONTAL VENTING
If it is not feasible to provide separate exhaust ducts for each dryer, ducts for individual dryers may be channeled
into a common main duct. Each dryer is provided with a back draft damper. The individual ducts should enter the
bottom or side of the main duct at an angle not more than 45º in the direction of the airflow. No more than eight
(8) dryers should be connected to one (1) main common duct run.
The main common duct may be any shape so long as the minimum cross-sectional area is provided. The main
duct should be tapered with the diameter increasing before each individual 8-inch (20.32 cm) duct is added
(refer to Illus. C below and Illus. D on page 16).
Illus. C
Horizontal venting must not exceed 35 feet (10.7 meters), this calculation compensates for the use of a
maximum of only one (1) elbow, which is the outside outlet protection.
NOTE: Distance between dryer single ducts being connected to the main common duct must be a
minimum of 28-1/2” (72.39 cm) dryer width.
Ductwork should be laid out in such a manner where allowances are made at rear area of the
dryer for removal of rear service panels or guards.
Illus. C (refer to the above illustration) shows the minimum cross section area for horizontal multiple dryer
venting. These figures must be increased in proportion if the main duct run from the last dryer to where it
exhausts has numerous elbows or is unusually long.