Technical Information
68
T 80xx
exhaust the air without any problem. If the sum is greater than 66 ft., a
larger duct diameter may be required.
Type of bend or fitting Angle of bend Radius of bend Additional length factor
Smooth bend 90° 4 inches 14 inches
Elbow bend (Sharp – no
radius
90° 90 inches
Corrugated bend 90° 8 inches 28 inches
Flexible metal duct 45° Up to 16 inches 12 inches
90° Up to 16 inches 20 inches
Wall vent with flap 99 inches
Wall vent with louvers 142 inches
Calculating the maximum allowable length for 5" (125 mm) ducting
When using 5" ducting, adequate air extraction is possible for an effective
duct length of up to 115 ft. (1378 in.)
To calculate the effective duct length, proceed as follows:
A) Measure the total length of the proposed ducting, including any bends.
B) Determine the amount, angle, and type of bends that will be required.
C) Determine what type of fitting will be used to terminate the duct at the
outer wall (flap vent, louvered vent, grill, etc.).
D) Using the chart below, add the additional length factor of the bends and
fittings that will be used to the total length measured in Step A above. If
the sum is less than 115 ft. (1378 inches), the hood will be able to
exhaust the air without any problem. If the sum is greater than 115 ft., an
external fan may be required.
Type of bend or fitting Angle of bend Radius of bend Additional length factor
Smooth bend 45° 4 inches 8 inches
45° 8 inches 4 inches
90° 4 inches 12 inches
90° 8 inches 8 inches
Elbow bend 45° 18 inches
90° 71 inches
Corrugated bend 90° 22 inches
Flexible metal duct 45° 5 inches 8 inches
45° 10 inches 6 inches
45° 20 inches 4 inches
90° 5 inches 14 inches
90° 10 inches 12 inches
90° 20 inches 8 inches
R
Smooth Bend
90° Elbow
R
Corrugated Bend
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