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53
INSTALLATION INSTRUCTIONS
Gas Supply
Gas Piping
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. For gas pipe sizing in the United States,
refer to the National Fuel Gas Code, NFPA 54. For
Canadian gas pipe sizing, refer to the Natural Gas
and Propane Installation Code CAN/CSA B149.1.
The information below is provided as an example.
The appropriate table from the applicable code
must be used.
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.
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 2500 BTU/FT
3
. The gas input
of the tankless water heater is 199,900 BTU/
HR. Additional appliances at the location require
75,000 BTU/HR. Therefore, the cubic feet per
hour = (199,900 + 75,000)/2500 = 109 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.
Gas Input of
Cubic Feet Water Heater (BTU/HR)
Per Hour (CFH) = Heating Value of Gas (BTU/FT
3
)
Pipe-Sizing Table – Natural Gas
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
(Capacity in cubic feet per hour)
Length
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
Pipe-Sizing Table – Propane Gas
Schedule 40 Metallic Pipe
Inlet Pressure: 11.0 inches W.C.
Pressure Drop: 0.5 inches W.C.
Specific Gravity: 1.50
(Capacity in cubic feet per hour)
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
Refer to current National Fuel Gas Code, NFPA 54.