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Total factored length multipliers:
System component
Multiplying
Factor
Total length of piping, in feet (horizontal &
vertical straight)
x1
Horizontal run length, in feet x3
90 degree elbows or tees x5
45 degree elbow x3
Each 1000 feet of altitude above sea level x1.5
Figure 3
If the total factored length is under 30, use a 3 or 4-inch exhaust system
If the total factored length is 30 or greater, use a 4-inch exhaust system
Example 1: An exhaust system going straight out the wall with 2 feet horizontal PL vent, into a
TEE with a clean out cap, then running vertical for 5 feet, then into a 90 degree elbow and
terminating with a 45 degree elbow, installed at sea level.
Example 2: The same system as in example 1 installed at an elevation of 6,000 feet. To estimate
the size of the exhaust system use the following factors:
VARIABLES Example 1 Example 2
Total length of exhaust system, in feet
7 7
3 feet for each foot of horizontal run.
(3 x 2) = 6 (3 x 2) = 6
5 feet for each 90 degree elbow or tee
(5 x 2) = 10 (5 x 2) = 10
3 feet for each 45 degree elbow
(3 x 1) = 3 (3 x 1) = 3
1.5 feet for each 1,000 feet of altitude
(1.5 x 0) = 0 (1.5 x 6) = 9
Total Factored Length
26 35
Required size of exhaust system
3 or 4” 4”
Figure 4
NOTE: 4 inch PL vent may be used in any installation. Always increase up to a 4” exhaust
system if in question as to the size pellet vent pipe to use.
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