44
RT-SVX063E-EN
Table 12.
Sizing natural gas pipe mains and branches
Gas SupplyPipe Run
(ft)
Gas Input (Cubic Feet/Hour)
1¼" Pipe
1½" Pipe
2" Pipe
2½" Pipe
3" Pipe
4" Pipe
10
1,060
1,580
3,050
4,860
8,580
17,500
20
726
1,090
2,090
3,340
5,900
12,000
30
583
873
1,680
2,680
4,740
9,660
40
499
747
1,440
2,290
4,050
8,270
50
442
662
1,280
2,030
3,590
7,330
60
400
600
1,160
1,840
3,260
6,640
70
368
552
1,060
1,690
3,000
6,110
80
343
514
989
1,580
2,790
5,680
90
322
482
928
1,480
2,610
5,330
100
304
455
877
1,400
2,470
5,040
125
269
403
777
1,240
2,190
4,460
150
244
366
704
1,120
1,980
4,050
175
224
336
648
1,030
1,820
3,720
200
209
313
602
960
1,700
3,460
Notes:
1
.
Table is based upon specific gravity of 0.60. Refer to the latest edition of the National Fuel Gas Code, Z223.1, unless superseded by local gas codes.
2
.
If more than one unit is served by the same main gas supply, consider the total gas input (cubic feet/hr.) and the total length when determining
the appropriate gas pipe size.
3
.
Obtain the Specific Gravity and BTU/Cu.Ft. from the gas company.
4
.
The following example demonstrates the considerations necessary when determining the actual pipe size:
Example: A 40' pipe run is needed to connect a unit with a 850 MBH furnace to a natural gas supply having a rating of 1,000 BTU/Cu.Ft. and a
specific gravity of 0.60
Cu.Ft/Hour = Furnace MBH Input
Gas BTU/Cu.Ft. X Multiplier
Table 13, p. 44
Cu.Ft/Hour = 850
The above table indicates that a 2" pipe is required.
Table 13.
Specific gravity multipliers
Specific
Gravity
Multiplier
0.50
1.10
0.55
1.04
0.60
1.00
0.65
0.96
Table 14.
Natural gas – high altitude gas input rating reduction orifice chart
Heater size (MBh)
0-2000'
3000'
4000'
5000'
6000'
7000'
8000'
9000'
10000'
250
#34
#36
#36
#37
#37
#38
#39
#40
#42
350
#32
#34
#35
#35
#36
#36
#37
#38
#40
500
#34
#36
#36
#37
#37
#38
#39
#40
#42
850
#34
#36
#36
#37
#37
#38
#39
#40
#42
1200
3.00 mm
#34
#35
#35
#36
#36
#37
#38
#40
Note:
Orifice sizes required to reduce input ratings by 4% per every 1000’ above 2000’ per the National Fuel Gas Code Z223.1.
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