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E. EXHAUST REQUIREMENTS
1. General Exhaust Ductwork Information
Exhaust ductwork should be designed and installed by a qualified professional. Improperly sized ductwork
will create excessive back pressure which results in slow drying, increased use of energy, overheating of the
dryer, and shutdown of the burner by the airflow (sail) switches, burner hi-limits, or basket (tumbler) hi-heat
thermostats.
CAUTION: DRYER MUST BE EXHAUSTED TO THE OUTDOORS.
CAUTION: IMPROPERLY SIZED or INSTALLED EXHAUST DUCTWORK CAN
CREATE A POTENTIAL FIRE HAZARD.
NOTE: When a dryer is exhausted separately, it is recommended that a back draft damper be
installed.
NOTE: When dryers are exhausted into multiple (common) exhaust lines, each dryer must be supplied
with a back draft damper.
The ductwork 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. Single or independent dryer venting is recommended. When single
dryer venting is used, the ductwork from the dryer to the outside exhaust outlet must not exceed 20 feet
(6.1 meters). In the case of multiple (common) dryer venting, the distance from the last dryer to the outside
exhaust outlet must not exceed 20 feet (6.1 meters). The shape of the ductwork is not critical so long as
the minimum cross section area is provided. It is suggested that the use of 90º turns in ducting be avoided;
use 30º or 45º angles instead. The radius of the elbows should preferably be 1-1/2 times the diameter of
the duct. Excluding basket (tumbler) or dryer elbow connection in the exhaust duct run. If more than two
(2) elbows are used, the cross section area of the ductwork must be increased in proportion to the number
of elbows added.
ALL ductwork should be smooth inside with no projections from the sheet metal screws or other obstructions,
which will collect lint. When adding ducts, the duct to be added should overlap the duct to which it is to be
connected. ALL ductwork joints must be taped to prevent moisture and lint from escaping into the building.
Inspection doors should be installed at strategic points in the exhaust ductwork for periodic inspection and
cleaning of lint from the ductwork.
IMPORTANT: Exhaust back pressure measured by a manometer at each basket (tumbler) duct area
must not exceed 0.3 inches (0.75 mb) of water column (W.C.).
IMPORTANT: When the exhaust ductwork passes through a wall, ceiling, or roof made of
combustible materials, the opening must be 2-inches (5.08 cm) larger than the duct
(ALL the way around). The duct must be centered within this opening.
a. Outside Ductwork Protection
1) To protect the outside end of horizontal ductwork from the weather, a 90° elbow bent downward
should be installed where the exhaust exits the building. If the 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.