507581-05
Page 25 of 62
Issue 2220
Figure 32. (Inlet Air from Ventilated Crawlspace and
Outlet Air to Outside)
NOTE
-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
2
per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
Roof Terminated
Exhaust Pipe
Furnace
Ventilation
Louvers
(Crawl space)
*Intake Debris Screen Provided)
Inlet Air
(Minimum
12 in.(305mm)
Above crawl
space floor)
Coupling or
3 in. to 2 in.
Transition
(Field Provided)
* See Maximum Vent Lengths table
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
Figure 33. Insulating Exhaust Pipe in an
Unconditioned Space
Maximum Allowable Exhaust Vent Pipe Length
3
(in ft.) without Insulation in Unconditioned Space for Winter
Design Temperatures
Winter Design Temperatures
1
ºF
(ºC)
Vent Pipe
Diameter
Unit Input Size
030
045
070
090
110
PVC
2
PP
PVC
2
PP
PVC
2
PP
PVC
2
PP
PVC
2
PP
32 to 21
(0 to -6)
1-1/2 in.
N/A
N/A
22
N/A
20
N/A
N/A
N/A
N/A
N/A
2 in.
13
12
21
18
33
30
46
42
30
30
2-1/2 in.
10
N/A
16
N/A
26
N/A
37
N/A
36
N/A
3 in.
6
6
12
12
21
21
30
30
29
29
20 to 1
(-7 to -17)
1-1/2 in.
N/A
N/A
12
N/A
20
N/A
N/A
N/A
N/A
N/A
2 in.
6
4
11
9
19
17
28
25
27
24
2-1/2 in.
N/A
N/A
7
N/A
14
N/A
21
N/A
20
N/A
3 in.
N/A
N/A
N/A
N/A
9
9
16
16
14
14
0 to -20
(-18 to -29)
1-1/2 in.
N/A
N/A
8
N/A
13
N/A
N/A
N/A
N/A
N/A
2 in.
N/A
N/A
6
4
12
10
19
16
18
15
2-1/2 in.
N/A
N/A
N/A
N/A
7
N/A
13
N/A
12
N/A
3 in.
N/A
N/A
N/A
N/A
N/A
N/A
8
8
7
7
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 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
Table 6.