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TABLE 6
Maximum Allowable Vent Pipe Length (in ft.) Without Insulation In Unconditioned Space
For Winter Design Temperatures Modulating High Efficiency 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
2 in.
11
9
14
12
18
15
N/A
N/A
2-1/2 in
7
N/A
10
N/A
12
N/A
3 in.
N/A
6
6
8
8
13
13
20 to 1
(-7 to -17)
2 in.
6
4
8
6
N/A
N/A
2-1/2 in.
N/A
N/A
N/A
N/A
3 in.
0 to -20
(-18 to -29)
2 in.
2-1/2 in.
3 in.
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.
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 figure21.
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
FIGURE 21
