16
305, 505, 705 Indoor Manual
Pipe Sizing Procedure - 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 propane gas for your location is 2516 BTU / FT
3
.
The gas input is 190,000 BTU/HR. Additional appliances at the location require 75,000 BTU/HR.
Therefore the cubic feet per hour = (190,000+75,000) / 2516 = 105.3 FT
3
/ HR.
If the pipe length is 100 ft then the 3/4 inch pipe size capable of supplying 197 FT
3
/ HR of propane gas
will be adequate.
Pipe Sizing Table - Natural Gas
Pipe Sizing Table - Propane Gas
Pipe Size (inches)
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
Length
Length
Pipe Size (inches)
1/2 3/4 1 1
1/4
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
Inlet Pressure: less than 2 psi (55 inches W.C.)
Pressure Drop: 0.3 inches W.C.
Specific Gravity: 0.60
Inlet Pressure: 11.0 inches W.C.
Pressure Drop: 0.5 inches W.C.
Specific Gravity: 1.50
Schedule 40 Metallic Pipe
cubic feet per hour
Schedule 40 Metallic Pipe
cubic feet per hour
Gas Piping
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.
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