18
3. Multiple Dryer (common) Venting
If it is not feasible to provide separate exhaust ducts for each dryer, ducts from individual dryers may be
channeled into a "common main duct." The individual ducts should enter the bottom or side of the main duct
at an angle not more than 45º in the direction of airflow and
should be
spaced at least 46-inches (116.84
cm) apart. The main duct
should be
tapered, with the diameter increasing before each individual duct (16-
inch [40.64 cm] minimum) is added.
IMPORTANT
: The ML-96
is not
provided with a back draft damper unless the damper option was
purchased. When exhausted into a multiple (common) exhaust line, a back draft
damper
must be
installed at each dryer duct.
IMPORTANT
: No more than three (3) dryers
should be
connected to main common duct.
The main duct may be any shape so long as the minimum cross section is provided. The illustration on
page
19
shows the minimum cross section area for multiple dryer round or square venting. These figures
must
be
increased 10 square inches (64.5 square centimeters) when rectangular main ducting is used, and the
ratio of duct width to depth
should not
be
greater than 3-1/2 to 1. These figures
must be
increased in
proportion if the main duct run from the last dryer to where it exhausts to the outdoors is unusually long (over
20 feet [6.1 meters]) or has numerous (more than two [2] elbows in it). In calculating ductwork size, the
cross section area of a square or rectangular duct
must be
increased twenty percent (20%) for each
additional 20 feet (6.1 meters). The diameter of a round exhaust
must be
increased ten percent (10%) for
each additional 20 feet (6.1 meters). Each 90º elbow is equivalent to an additional 36 feet (10.97 meters)
and each 45º elbow is equivalent to an additional 15 feet (4.57 meters).
IMPORTANT
: For extended ductwork runs, the cross section area of the ductwork can only be
increased to an extent. Maximum proportional ductwork runs
cannot
exceed 15 feet
(4.57 meters) with two (2) elbows. When the ductwork approaches the maximum
limits as noted in this manual, a professional heating, venting, and air conditioning
(HVAC) firm
should be
consulted for proper venting information.
IMPORTANT
: Exhaust back pressure measured by a manometer at each dryer exhaust duct area
must not
exceed
0.3 inches (0.75 mb) of water column (W.C.).
The 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.
NOTE
: 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.