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Roof Terminated
Exhaust Pipe
Ventilation
Furnace
Louvers
(Crawl space)
Coupling or
3 in. to 2 in.
Transition
(Field Provided)
* See Maximum Vent Lengths table
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
hour of the total input rating of all equipment in the enclosure.
Figure 32. (Inlet Air from Ventilated Crawlspace and
Outlet Air to Outside)
Maximum Allowable Exhaust Vent Pipe Length
Winter Design Temperatures
(ºC)
32 to 21
(0 to -6)
20 to 1
(-7 to -17)
0 to -20
(-18 to -29)
Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
1
Poly-Propylene vent pipe (PP) by Duravent and Centrotherm
2
Vent length in table is equivalent length. Each elbow is equivalent to 5ft. of straight pipe and should be included when measuring
3
total length.
NOTE - Concentric terminations are the equivalent of 5ft. 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 5A through Table 5C or Table 6.
NOTE - If insulation is required in an unconditioned space, it must be located on the pipe closest to the furnace. See Figure 33.
508390-01
Inlet Air
(Minimum
12 in.(305mm)
Above crawl
space floor)
*Intake Debris Screen Provided)
2
per 1.17kW) per
Design Temperatures
ºF
Vent Pipe
1
Diameter
PVC
1-1/2 in.
2 in.
2-1/2 in.
3 in.
1-1/2 in.
2 in.
2-1/2 in.
3 in.
1-1/2 in.
2 in.
2-1/2 in.
3 in.
Conditioned
Figure 33. Insulating Exhaust Pipe in an
(in ft.) without Insulation in Unconditioned Space for Winter
3
030
045
PP
PVC
PP
2
2
N/A
N/A
22
N/A
13
12
21
18
10
N/A
16
N/A
6
6
12
12
N/A
N/A
12
N/A
6
4
11
9
N/A
N/A
7
N/A
N/A
N/A
N/A
N/A
N/A
N/A
8
N/A
N/A
N/A
6
4
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Table 6.
Issue 2327
Conditioned
Space
Pipe Insulation
Unconditioned
Space
Space
Unconditioned Space
Unit Input Size
070
090
PVC
PP
PVC
2
20
N/A
N/A
33
30
46
26
N/A
37
21
21
30
20
N/A
N/A
19
17
28
14
N/A
21
9
9
16
13
N/A
N/A
12
10
19
7
N/A
13
N/A
N/A
8
Exhaust
Pipe
Intake
Pipe
110
PP
PVC
PP
2
2
N/A
N/A
N/A
42
30
30
N/A
36
N/A
30
29
29
N/A
N/A
N/A
25
27
24
N/A
20
N/A
16
14
14
N/A
N/A
N/A
16
18
15
N/A
12
N/A
8
7
7
Page 25 of 60
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