Page 39
31-5000724 Rev. 0
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
Figure 26. Insulating Exhaust Pipe in an Unconditioned Space
Maximum Allowable Vent Pipe Length
3
without Insulation in Unconditioned Space for Winter Design Temperatures
Modulating High Efficiency Furnace
Winter Design Temperatures
1
ºF (ºC)
Vent Pipe
Diameter
070
090
110
32 to 21
(0 to -6)
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
2 in.
11
9
14
12
18
15
2-1/2 in.
7
N/A
10
N/A
12
N/A
3 in.
N/A
N/A
6
6
8
8
20 to 1
(-7 to -17)
1-1/2 in.
N/A
N/A
N/A
N/A
N/A
N/A
2 in.
N/A
N/A
6
4
8
6
2-1/2 in.
N/A
N/A
N/A
N/A
N/A
N/A
3 in.
N/A
N/A
N/A
N/A
N/A
N/A
0 to -20
(-18 to -29)
1-1/2 in.
N/A
N/A
N/A
N/A
N/A
N/A
2 in.
N/A
N/A
N/A
N/A
N/A
N/A
2-1/2 in.
N/A
N/A
N/A
N/A
N/A
N/A
3 in.
N/A
N/A
N/A
N/A
N/A
N/A
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
3
Vent length in table is equivalent length. Each elbow is equivalent to 5ft of straight pipe and should be included when measuring
total 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 23A or Table 23B.
NOTE
- If insulation is required in an unconditioned space, it must be located on the pipe closest to the furnace. See Figure 34.
Table 21.
