to calculate total equivalent ductwork length using the approximate feet of equivalent
length of some typical ducts.
DUCT PIECES
EQUIVALENT
LENGTH
x
NUMBER
USED
=
EQUIVALENT
LENGTH
Rectangular-to-
Round Transition
Adaptor*
5 Ft. (1.5 m) x ( ) = Ft. or m
Wall Cap 40 Ft. (12.2 m) x ( ) = Ft. or m
90° Elbow 10 Ft. (3 m) x ( ) = Ft. or m
45° Elbow 5 Ft. (1.5 m) x ( ) = Ft. or m
90° Elbow 25 Ft. (7.6 m) x ( ) = Ft. or m
45° Elbow 5 Ft. (1.5 m) x ( ) = Ft. or m
Roof Cap 24 Ft. (7.3 m) x ( ) = Ft. or m
Straight Duct 6"
(15.2 cm) Round or
3
1
⁄
4
" x 10"
(8.2 x 25.4 cm
Rectangular)
1 Ft. (0.3 m) x ( ) = Ft. or m
Total Ductwork = Ft. or m
* IMPORTANT: If a rectangular-to-round transition adaptor is used,
the bottom corners of the damper will have to be cut to fit, using
the tin snips, in order to allow free movement of the damper.
Equivalent lengths of duct pieces are based on actual tests and reflect requirements for
good venting performance with any vent hood.
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