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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 (645 mm
1.17 kW) per hour of the total input rating of all equipment in the
enclosure.
Figure 32. Equipment in Confined Space
(Inlet Air from Ventilated Crawl Space & Outlet Air to
Maximum Allowable Exhaust Vent Pipe Length (in ft.) without Insulation in Unconditioned Space for Winter Design
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
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 and Table 5B or Table 6A through Table 6C.
NOTE - If insulation is required in an unconditioned space, it must be located on the pipe closest to the furnace. See Figure 33.
507270-03
Inlet Air
Minimum
12 in. (305mm)
above Crawl
Space Floor
*Intake Debris Screen Provided
Outside)
Temperatures Single - Stage High Efficiency Furnace
ºF
Vent Pipe
1
Diameter
2 in.
2-1/2 in.
3 in.
2 in.
2-1/2 in.
3 in.
2 in.
2-1/2 in.
3 in.
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.
per
2
Figure 33. Insulating Exhaust Pipe in an
045
070
PVC
PP
PVC
2
18
16
31
13
N/A
24
9
9
18
9
8
18
5
N/A
13
N/A
N/A
8
5
3
12
N/A
N/A
7
N/A
N/A
N/A
Table 7.
Issue 1809
Conditioned
Space
Pipe Insulation
Conditioned
Unconditioned
Space
Space
Unconditioned Space
Unit Input Size
090
110
PP
PVC
PP
PVC
2
2
28
50
48
30
N/A
42
N/A
56
18
35
35
47
16
32
29
30
N/A
24
N/A
34
8
19
19
26
10
22
19
30
N/A
15
N/A
22
N/A
10
10
16
Exhaust
Pipe
Intake
Pipe
135
PP
PVC
PP
2
2
30
N/A
N/A
N/A
N/A
N/A
47
52
52
30
N/A
N/A
N/A
N/A
N/A
26
30
30
27
N/A
N/A
N/A
N/A
N/A
16
18
18
Page 27 of 59
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