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TABLE 23
Maximum Allowable Exhaust Vent Pipe Length (in ft.)Without Insulation In Unconditioned Space For
Winter Design Temperatures Two - Stage High Efficiency Furnace
Winter Design
Temperatures
1
°F (°C)
Vent Pipe
Diameter
Unit Input Size
040
060
080
32 to 21
(0 to -6)
PVC
2
PP
PVC
2
PP
PVC
2
PP
2 in.
21
18
33
30
46
42
2-1/2 in.
16
N/A
26
N/A
37
N/A
3 in.
12
12
21
21
30
30
20 to 1
(-7 to -17)
2 in
11
9
19
17
28
25
2-1/2 in.
7
N/A
14
N/A
21
N/A
3 in.
N/A
N/A
9
9
16
16
0 to -20
(-18 to -29)
2 in.
6
4
12
10
19
16
2-1/2 in.
N/A
N/A
7
N/A
13
N/A
3 in.
N/A
N/A
N/A
N/A
8
8
1
Refer 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 21 or 22 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 figure24.
FIGURE 24
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
