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TABLE 9
Maximum Allowable Exhaust Vent Pipe Length 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
045
070
090
110
135
32 to 21
(0 to -6)
PVC
PVC
PVC
PVC
PVC
2 in.
20
30
40
24
N/A
2-1/2 in.
15
22
30
40
N/A
3 in.
12
18
25
32
42
20 to 1
(-7 to -17)
2 in
12
20
25
24
N/A
2-1/2 in.
10
14
20
24
N/A
3 in.
6
10
15
20
22
0 to -20
(-18 to -29)
2 in.
8
12
18
22
N/A
2-1/2 in.
6
8
12
16
N/A
3 in.
2
6
10
12
15
1
Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
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 7 or 8 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 figure28.
FIGURE 28
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
