507581-04
Issue 1933
Page 25 of 59
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
General Guidelines for Vent Terminations
In Non–Direct Vent applications, combustion air is taken
from indoors and the flue gases are discharged to the
outdoors. This furnace is then classified as a non–direct
vent, Category IV gas furnace.
In Direct Vent applications, combustion air is taken from
outdoors and the flue gases are discharged to the outdoors.
The furnace is then classified as a direct vent, Category IV
gas furnace.
Table 6.
Maximum Allowable Exhaust Vent Pipe Length (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
32 to 21
(0 to -6)
PVC
2
PP
PVC
2
PP
PVC
2
PP
PVC
2
PP
PVC
2
PP
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)
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)
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
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 5A through Table 5C or Table 6.
NOTE
