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Duct Preparation
Higher volumes of air exhausted by the vent system result in better overall removal
of smoke and fumes from the kitchen. Longer duct runs and greater numbers of
duct transitions reduce air volume, therefore it is extremely important to keep
duct runs as short and straight as possible.
We recommend using a certified HVAC contractor for all installations.
To ensure that your installation
meets this requirement, add the
actual straight length of duct to the
equivalent straight length of all duct
fittings to determine the total
equivalent straight length of duct.
(Refer to the table on the right,
which shows various common duct
fittings with their equivalent straight
lengths for various common duct
sizes). If this total equivalent
straight length is less than or equal
to the maximum limits specified,
then the installation is proper.
Consider the duct size that
corresponds to the majority of the duct used in the installation.
Sample problem - for reference only:
Given a system installation having 25 feet of 3 ¼” x 10” rectangular duct, one (1)
90-degree 3 ¼” x 10” elbow, and one (1) 3 ¼” x 10” to 10” round transition, would
this installation be proper?
Solution:
1. Add the total length of straight duct:
25’ (of 3 ¼” x 10”) = 25’.
2. Using Table above, determine the equivalent straight length of all duct fittings:
90-degree 3 ¼” x 10” elbow = 15’. 3 ¼” x 10” to 10” round transition = 4’.
E30DD75ESS
E36DD75ESS
E46DD75ESS
E48DD75ESS
Maximum Equivalent Straight LengthsModel Duct
Size
3 1/4” x 10” 60’
70’
3 1/4" x 10" 90° Elbow 3 1/4" x 10" 45° Elbow 3 1/4" x 10" Wall Cap 3 1/4" x 10"
90° Flat Elbow
Transistion
3 1/4" x 10" to Round
45° Elbow - Round Duct 90° Transistion
3 1/4" x 10" to 10" Round
90° Elbow - Round Duct
15 Feet 7 Feet 2 Feet 20 Feet
10" Diameter - 4 Feet
10" Diameter - 2 Feet
25 Feet
10" Diameter - 5 Feet
10”