a. Permanently install perforated disk assembly (factory-
supplied in loose parts bag) in combustion-air elbow
using RTV or by cementing. (See Fig. 35.)
For 120,000 Btuh size units only: Separate the 2 halves
of perforated disk assembly and use only the shouldered
disk half.
b. Determine length of straight portion of combustion-air
inlet pipe from table in Fig. 35.
c. Cut field-supplied 2-in diameter PVC pipe to determined
length.
d. Permanently attach elbow/perforated disk assembly to
straight portion of pipe using RTV or by cementing. (See
Fig. 35.)
TABLE 6—MAXIMUM ALLOWABLE PIPE LENGTH (FT) (CONTINUED)
ALTITUDE (FT) UNIT SIZE
TERMINATION
TYPE
PIPE DIA
(IN.)*
NUMBER OF 90° ELBOWS
123456
4001 to 5000‡
024040
036040
2 Pipe or 2-in
Concentric
1-1/2 60 55 50 45 44 39
2 707070707070
024060
036060
048060
2 Pipe or 2-in
Concentric
1-1/2 15 10 5 NA NA NA
2 645958535252
036080
048080
060080
2 Pipe or 2-in
Concentric
2 443926212011
2-1/2 70 70 70 70 70 70
048100
060100
2 Pipe or 3-in
Concentric
2-1/2 31 22 13 12 NA NA
3 707067625752
060120
2 Pipe or 3-in.
Concentric
3† no disk 53 46 40 33 26 20
4† no disk 70 70 70 70 70 70
ALTITUDE (FT) UNIT SIZE
TERMINATION
TYPE
PIPE DIA
(IN.)*
NUMBER OF 90° ELBOWS
123456
5001 to 6000‡
024040
036040
2 Pipe or 2-in
Concentric
1-1/2 57 52 47 42 40 35
2 707070707070
024060
036060
048060
2 Pipe or 2-in
Concentric
1-1/2 14 9 NA NA NA NA
2 605554494847
036080
048080
060080
2 Pipe or 2-in
Concentric
2 4136231817 8
2-1/2 70 70 70 70 70 70
048100
060100
2 Pipe or 3-in
Concentric
2-1/2 29 21 12 11 NA NA
3 706762575247
060120
2 Pipe or 3-in.
Concentric
3† no disk 42 35 29 22 15 9
4† no disk 70 70 70 70 70 70
ALTITUDE (FT) UNIT SIZE
TERMINATION
TYPE
PIPE DIA
(IN.)*
NUMBER OF 90° ELBOWS
123456
6001 to 7000‡
024040
036040
2 Pipe or 2-in
Concentric
1-1/2 53 48 43 38 37 32
2 707068676664
024060
036060
048060
2 Pipe or 2-in
Concentric
1-1/2 13 8 NA NA NA NA
2 575250454443
036080
048080
060080
2 Pipe or 2-in
Concentric
2 3833211615 6
2-1/2 70 70 68 67 66 64
048100
060100
2 Pipe or 3-in
Concentric
2-1/2 27 19 10 9 NA NA
3 686358534843
060120
2 Pipe or 3-in.
Concentric
3† no disk 31 24 18 11 NA NA
4† no disk 70 70 70 70 67 62
ALTITUDE (FT) UNIT SIZE
TERMINATION
TYPE
PIPE DIA
(IN.)*
NUMBER OF 90° ELBOWS
123456
7001 to 8000‡
024040
036040
2 Pipe or 2-in
Concentric
1-1/2 49 44 39 34 33 28
2 666563626059
024060
036060
048060
2 Pipe or 2-in
Concentric
1-1/2 12 7 NA NA NA NA
2 534846414038
036080
048080
060080
2 Pipe or 2-in
Concentric
2 3631191412NA
2–1/2 66 65 63 62 60 59
048100
060100
2 Pipe or 3-in
Concentric
2–1/2 25 17 8 7 NA NA
3 635853484338
060120
2 Pipe or 3-in.
Concentric
3† no disk 20 13 7 NA NA NA
4† no disk 61 56 51 46 41 36
See notes at end of table
—26—
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