-- 42 --
Table 11—Maximum Allowable Pipe Length --- Ft (M) (Continued)
ALTITUDE (FT)
UNIT SIZE
(BTUH)
DIRECT VENT (2-PIPE) ONLY
NON-DIRECT
VENT (1-PIPE)
ONLY
NUMBER OF 90
°
ELBOWS
TERMINATION
TYPE
PIPE DIA
IN. (mm)*
PIPE DIA
IN. (mm)*
1
2
3
4
5
6
9001 to 10,000‡
(2743 to 3048)
40,000
2 Pipe or 2-in
1-1/2 (38)
1-1/2 (38)
42
(12.8)
37
(11.3)
32
(9.8)
27
(8.2)
25
(7.6)
20
(6.1)
Concentric
2 (51)
2 (51)
57
(17.4)
55
(16.8)
53
(16.2)
51
(15.5)
49
(14.9)
47
(14.3)
60,000
2 Pipe or 2-in
Concentric
2 (51)
2 (51)
45
(13.7)
40
(12.2)
38
(11.6)
33
(10.1)
31
(9.4)
29
(8.8)
80,000
2 Pipe or 2-in
Concentric
2 (51)
2 (51)
30
(9.1)
25
(7.6)
14
(4.3)
9
(2.7)
7
(2.1)
NA
2-1/2 (64)
2-1/2 (64)
57
(17.4)
55
(16.8)
53
(16.2)
51
(15.5)
49
(14.9)
47
(14.3)
100,000
2 Pipe or 3-in
Concentric
2-1/2 (64)
2-1/2 (64)
21
(6.4)
13
(4.0)
5
(1.5)
NA
NA
NA
3 (76)
3 (76)
54
(16.5)
49
(14.9)
44
(13.4)
39
(11.9)
34
(10.4)
29
(8.8)
120,000
2 Pipe or 3-in.
Concentric
NA
3 (76)†
39
(11.9)
37
(11.3)
35
(10.7)
33
(10.1)
31
(9.4)
29
(8.8)
4 (102)† no
disk
4 (102)† no disk
10
(3.0)
5
(1.5)
NA
NA
NA
NA
* Disk usage-Unless otherwise specified, use perforated disk assembly (factory-supplied in loose parts bag).
# If one disk is stated, separate 2 halves of perforated disk assembly and use shouldered disk half. When using shouldered disk half, install screen side toward inlet box.
† Wide radius elbow.
‡ Vent sizing for Canadian installations over 4500 ft (1370 M) above sea level are subject to acceptance by the local authorities having jurisdiction. NA-Not Allowed;
pressure switch will not make.
NOTES
:
1. Do not use pipe size greater than those specified in table or incomplete combustion, flame disturbance, or flame sense lockout may occur.
2. Size both the combustion-air and vent pipe independently, then use the larger diameter for both pipes.
3. Assume two 45
°
elbows equal one 90
°
elbow. Wide radius elbows are desirable and may be required in some cases.
4. Elbows and pipe sections within the furnace casing and at the vent termination should not be included in vent length or elbow count.
5. The minimum pipe length is 5 ft (1.5 M) for all applications.
6. Use 3-in. (76 mm) diameter vent termination kit for installations requiring 4-in (102 mm) diameter pipe.
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
NOT IN
HORIZONTAL
SECTION
A93034
Fig. 39 -- Combustion--Air and Vent Pipe Diameter
Transition Location and Elbow Configuration
COMBUSTION-AIR
PIPE (DIRECT
VENT/2 PIPE)
BURNER
BOX
COMBUSTION – AIR
INTAKE HOUSING
3/8 ID TUBE
TRAP
TO OPEN
DRAIN
3/16
DRILL
4
″
MIN
(102 mm)
COMBUSTION-AIR
PIPE (NON-DIRECT
VENT/1-PIPE)
A05093
Fig. 40 -- Air Intake Housing Plug Fitting Drain
