STEP 2: Prepare The Venting System
Standard Fittings
NOTE: If the existing duct is round, you must use a
Duct Length
The total length of the duct system, including straight duct, elbows, transitions, and wall or roof caps must not
exceed 140 feet.
For best performance, do not use more than three 90 degree elbows, and keep the length as short as possible.
Below are the standard fittings and their equivalent length in feet.
1
3 1/4” x 10” to 6" = 5 ft.
2
3 1/4” x 10” roof cap = 24 ft
3
3 1/4” x 10” 90˚ elbow = 25 ft
4
90˚elbow
= 10 ft
5
3 1/4” x 10” wall cap = 40 ft
6
45˚elbow
= 5 ft
7
3 1/4” x 10” flat elbow = 10 ft
Figure 10
To calculate the equivalent length of each duct piece used, see the examples below.
Examples
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| For 3 1/4" x 10" SYSTEMS |
| For 6" ROUND SYSTEMS | wall cap | |||||||||||||
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| 6ft. |
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| transition | 2ft. |
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| 2ft. |
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1 3 1/4” x 10” 90° elbow | = | 25 ft. | 2 90° elbows |
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1 Wall Cap | = | 40 ft. | 1 Wall Cap |
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8 feet straight duct | = | 8 ft. | 8 feet straight | = | 8 ft. | |||||||||||||
TOTAL LENGTH | = | 73 ft. | TOTAL LENGTH | = | 73 ft. | |||||||||||||
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– 9 –