American Dryer Corp. Gas HSI - Phase 7/FSS AD-78 III - Manual (Page 19)

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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 shut down of the burner by the airflow (sail) switches, burner hi-limits, or basket (tumbler) hi-limit
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 the 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). 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-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.