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Pipe Sizing Procedure - Example
The gas supply must be capable of handling the entire gas load at the location. Gas line sizing is based on gas type,
the pressure drop in the system, the gas pressure supplied, and gas line type. Refer to the National Fuel Gas Code,
NFPA 54, for proper gas line sizing. The below information is provided as an example.
1. Determine the cubic feet per hour of gas required by dividing the gas input (on the rating plate) by the heating value
of the gas (available from the local gas company). The gas input needs to include all gas products at the location
and the maximum BTU usage at full load when all gas products are in use.
Gas Input of the water heater (BTU / HR)
Cubic Feet per Hour (CFH) -
Heating Value of Gas (BTU / FT 3 )
2. Use the table for your gas type to find the pipe size required for your cubic feet per hour of gas and your pipe
length.
Example: The heating value of natural gas for your location is 1020 BTU/FT 3
The gas input is 199,000 BTU/HR. Additional appliances at the location require 75,000 BTU/HR.
Therefore the cubic feet per hour = (199,000 + 75,000) / 1020 = 268.6 FT3/HR.
If the pipe length is 100 ft then the 1 1,/4inch pipe size capable of supplying 304 FT3/HR of natural gas will
be adequate.
TABLE 2: Pipe Sizing Table - Natural Gas
cubic feet per hour Schedule 40 Metallic Pipe
Inlet Pressure: less than 2 psi (55 inches W.C.)
Pressure Drop: 0.3 inches W.C.
Specific Gravity: 0.60
Pipe Size (inches)
Length
3/4 1 1 1/4 1 1/2
10 273 514 1060 1580
20 188 353 726 1090
30 151 284 583 873
40 129 243 499 747
50 114 215 442 662
60 104 195 400 600
70 95 179 368 552
80 89 167 343 514
90 83 157 322 482
100 79 148 304 455
125 70 131 269 403
150 63 119 244 366
175 58 109 224 336
200 54 102 209 313
TABLE 3: Pipe Sizing Table - Propane Gas
cubic feet per hour Schedule 40 Metallic Pipe
Inlet Pressure: 11 inches W.C.
Pressure Drop: 0.5 inches W.C.
Specific Gravity: 1.50
Pipe Size (inches)
Length
1/2 3/4 1 1 1
10 291 608 1150 2350
20 200 418 787 1620
30 160 336 632 1300
40 137 287 541 1110
50 122 255 480 985
60 110 231 434 892
80 101 212 400 821
100 94 197 372 763
125 89 185 349 716
150 84 175 330 677
175 74 155 292 600
200 67 140 265 543
12 305 & 505 Indoor Manual