American Dryer Corp. ML-75DIII - Manual (Page 18)

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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. The dryer must be installed with a proper exhaust duct connection to the outside.
CAUTION: This dryer produces combustible lint and must be exhausted to the outdoors.
CAUTION: DRYER MUST BE EXHAUSTED TO THE OUTDOORS.
CAUTION: IMPROPERLY SIZED OR INSTALLED EXHAUST DUCTWORK CAN
CREATE A POTENTIAL FIRE HAZARD.
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.
Horizontal Venting:
When single dryer venting is used, the length of ductwork from the dryer to the outside exhaust outlet, must
not exceed 15 feet (4.6 meters). The minimum diameter of this ductwork must be at least 10-inches
(25.4 cm). In the case of multiple (common) dryer venting, the distance from the last dryer to the outside
exhaust outlet must not exceed 15 feet (4.6 meters). The shape of the ductwork is not critical so long as
the minimum cross-sectional area is provided. It is suggested that the use of 90° turns be avoided; use 30°
and/or 45° angles instead. The radius of the elbows should preferably be 1-1/2 times the diameter of the
duct. Including basket (tumbler)/dryer elbow connections or elbows used for outside protection from the
weather, no more than two (2) elbows should be used in the exhaust duct run. If more than two (2)
elbows are used, the cross-sectional area of the ductwork must be increased. ALL ductwork should be
smooth inside with no projections from 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.
Vertical Venting:
When single dryer venting is used, the length of the ductwork from the dryer to the outside exhaust outlet
must not exceed 20 feet (6.1 meters). The minimum diameter of this ductwork must be at least
12-inches (30.48 cm) even though the dryer exhaust duct for gas and electric units is only 10-inches (25.4
cm). In the case of multiple (common) dryer venting, the distance from the last dryer to the outside exhaust
outlet should not exceed 20 feet (6.1 meters). The shape of the ductwork is not so critical so long as the
minimum cross-sectional area is provided. It is suggested that the use of 90º turns be avoided; use 30º and
/or 45º bends instead. The radius of the elbows should preferably be 1-1/2 times the diameter of the
duct. ALL ductwork should be smooth inside with no projections from 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 in the exhaust duct must be no less
than 0 and must not exceed 0.3 inches (0.74 mb) of water column (W.C.).