Maximum Duct Length; Elbows, Transitions, Wall And Roof Caps, Etc - Blomberg BOTR30200CSS Installation Manual

External exhaust
4

4.1.4 Maximum duct length

For satisfactory air movement, the total duct
1⁄4
length of 3 " x 10" (8.2 x 25.4 cm) rectangular or
6" (15.2 cm) diameter round duct should not ex-
ceed 120 equivalent feet (36.5 m).
4.1.5 Elbows, transitions, wall
and roof caps, etc.,
Present additional resistance to airflow and are
equivalent to a section of straight duct which is
longer than their actual physical size. When cal-
culating the total duct length, add the equivalent
lengths of all transitions and adaptors plus the
length of all straight duct sections. The chart be-
low shows you how to calculate total equivalent
ductwork length using the approximate feet of
equivalent length of some typical ducts.
Duct pieces
Rectangular-to-Round
Transition Adaptor*
Wall Cap
90° Elbow
45° Elbow
90° Elbow
10 / 63 EN
Equivalent
Length
5 Ft. (1.5 m)
40 Ft. (12.2 m)
10 Ft. (3 m)
45° Elbow
25 Ft. (7.6 m)
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