25
INSTALLATION INSTRUCTIONS FOR EXTERNAL EXHAUST DUCTING
NOTE: If you need to install ducts, note that the total duct length of 31/4” x 10”
(8.2 x 25.4 cm) rectangular or 5” (12.7cm) diameter / 6” (15.2 cm) diameter round duct
should not exceed 140 equivalent feet (42.7 m).
Outside ventilation requires an EXTERNAL EXHAUST DUCT.Read the following carefully.
NOTE: It is important that venting be installed using the most direct route and with as few
elbows as possible.
This ensures clear venting of exhaust and helps prevent blockages. Also, make sure
dampers swing freely and nothing is blocking the ducts.
Exhaust connection:
The exhaust adaptor has been designed to mate with a standard 31/4” x 10” (8.2 x 25.4 cm)
rectangular duct.
If a round duct is required, a rectangular-to-round transition adaptor must be used.
A5” (12.7c"m) / 6" (15.2cm) diameter duct is acceptable to use.
Maximum duct length:
For satisfactory air movement, the total duct length of 31/4” x 10” (8.2 x 25.4 cm)
rectangular or 5” (12.7cm) diameter / 6" (15.2cm) diameter round duct should not exceed
140 equivalentfeet (42.7 m).
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 calculating the total duct length, add the equivalent lengths of all transitions and
adaptors plus the length of all straight duct sections.
The chart below 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
45° Elbow
Roof Cap
Straight Duct 6“ (15.2 cm)
Round or 31⁄4“ x 10“
(8.2 x 25.4 cm Rectangular)
EQUIVALENT
LENGTH
5 Ft. (1.5 m) x ( ) =
40 Ft. (12.2 m) x ( ) =
10 Ft. (3 m) x ( ) =
5 Ft. (1.5 m) x ( ) =
25 Ft. (7.6 m) x ( ) =
5 Ft. (1.5 m) x ( ) =
24 Ft. (7.3 m) x ( ) =
1 Ft. (0.3 m) x ( ) =
Ft. or m
Ft. or m
Ft. or m
Ft. or m
Ft. or m
Ft. or m
Ft. or m
Ft. or m
Total Ductwork =
NUMBER
USED
EQUIVALENT
X
=
* 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.
