507867-02
Page 24 of 55
Issue 1933
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.
This furnace is then classified as a direct vent, Category IV
gas furnace.
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 (in ft.) without Insulation in Unconditioned Space for Winter Design
Temperatures Single - Stage High Efficiency Furnace
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
1-1/2 in.
N/A
N/A
25
N/A
25
N/A
N/A
N/A
N/A
N/A
2 in.
N/A
N/A
18
16
31
28
50
48
30
30
2-1/2 in.
N/A
N/A
13
N/A
24
N/A
42
N/A
56
N/A
3 in.
N/A
N/A
9
9
18
18
35
35
47
47
20
°
to 1
°
(-7 to -17)
1-1/2 in.
N/A
N/A
15
N/A
20
N/A
N/A
N/A
N/A
N/A
2 in.
N/A
N/A
9
8
18
16
32
29
30
30
2-1/2 in.
N/A
N/A
5
N/A
13
N/A
24
N/A
34
N/A
3 in.
N/A
N/A
N/A
N/A
8
8
19
19
26
26
0
°
to -20
°
(-18 to -29)
1-1/2 in.
N/A
N/A
10
N/A
15
N/A
N/A
N/A
N/A
N/A
2 in.
N/A
N/A
5
3
12
10
22
19
30
27
2-1/2 in.
N/A
N/A
N/A
N/A
7
N/A
15
N/A
22
N/A
3 in.
N/A
N/A
N/A
N/A
N/A
N/A
10
10
16
16
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 5 and Table 6.
NOTE
Table 7.
