Page 22
TABLE 9
Maximum Allowable Vent Pipe Length (in ft.
3
) Without Insulation In Unconditioned Space
For Winter Design Temperatures Modulating High Eciency Furnace
Winter Design
Temperatures1
°F (°C)
Vent Pipe
Diameter
Unit Input Size
070 090 110 135
32 to 21
(0 to -6)
PVC
2
PP PVC
2
PP PVC
2
PP PVC
2
PP
1-1/2 in. N/A N/A N/A N/A N/A N/A
N/A N/A2 in. 11 9 14 12 18 15
2-1/2 in 7 N/A 10 N/A 12 N/A
3 in. 2 2 6 6 8 8 13 13
20 to 1
(-7 to -17)
1-1/2 in. N/A N/A N/A N/A N/A N/A
N/A N/A2 in. 3 1 6 4 8 6
2-1/2 in. 1 N/A 1 N/A 3 N/A
3 in. 1 1 1 1 1 1 2 2
0 to -20
(-18 to -29)
1-1/2 in. N/A N/A N/A N/A N/A N/A
N/A N/A
2 in. 1 1 1 1 2 1
2-1/2 in. 1 N/A 1 N/A 1
N/A
3 in. 1 1 1 1 N/A
1Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
2 Poly-Propylene vent pipe (PP) by Duravent and Centrotherm.
3 Vent lengths in table are equivalent length. Consider each elbow as 5ft of linear length.
NOTE - Concentric terminations are the equivalent of 5’ and should be considered when measuring pipe length.
NOTE - Maximum uninsulated vent lengths listed may include the termination(vent pipe exterior to the structure) and cannot exceed 5 linear feet or the maximum allowable
intake or exhaust vent length listed in table 5 or which ever is less.
NOTE - If insulation is required in an unconditioned space, it must be located on the pipe closest to the furnace. See FIGURE 29.
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
FIGURE 29
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