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32
Table 8. Natural Gas Capacity (Cu. ft/hr)
Nominal Iron
Pipe Size, in.
Length of Pipe, Feet
Capacity of gas pipe of different diameters and lengths in cu. ft. per hr. with pressure drop of 0.3 in. and specific gravity of 0.60 (natural gas).
After the length of pipe has been determined, select the pipe size which will provide the minimum cubic feet per hour required for the
gas input rating of the water heater. By formula:
The gas input of the water heater is marked on the water heater data plate. The heating value of the gas (BTU/FT
3
) may be determined
by consulting the local natural gas utility.
10
132
278
520
1050
1600
1/2
3/4
1
1-1/4
1-1/2
20
n/a
190
350
730
1100
30
n/a
152
285
590
890
40
n/a
130
245
500
760
50
n/a
115
215
440
670
60
n/a
105
195
400
610
70
n/a
96
180
370
560
80
n/a
n/a
170
350
530
90
n/a
n/a
160
320
490
100
n/a
n/a
150
305
460
125
n/a
n/a
130
275
410
150
n/a
n/a
120
250
380
200
n/a
n/a
100
210
320
175
n/a
n/a
110
220
350
Cu. Ft. Per Hr. Required =
Gas Input of Water Heater (BTU/HR)
Heating Value of Gas (BTU/FT
3
)
Table 9. L.P. Gas Capacity
Nominal Iron
Pipe Size, in.
Length of Pipe, Feet
Maximum capacity of pipe in thousands of BTU per hour of undiluted liquefied petroleum gases (at 11 inches water column pressure).
Based on a Pressure Drop of 0.5 Inch Water Column.
Example: Input BTU requirement of the water heater, 199,000 BTUH
Total pipe length, 80 feet = 1" IPS required.
10
275
576
1071
2205
1/2
3/4
1
1-1/4
20
189
393
732
1496
30
152
315
590
1212
40
n/a
267
504
1039
50
n/a
237
448
913
60
n/a
217
409
834
70
n/a
196
378
771
80
n/a
185
346
724
90
n/a
173
322
677
100
n/a
162
307
630
125
n/a
146
275
567
150
n/a
132
252
511
Table 10. L.P. Gas Capacity
Copper Tubing
O.D. Size, in.
Length of Pipe, Feet
Maximum capacity of pipe in thousands of BTU per hour of undiluted liquefied petroleum gases (at 11 inches water column pressure).
Based on a Pressure Drop of 0.5 Inch Water Column.
Additional tables are available in the current edition of the “National Fuel Gas Code”, ANSI Z223.1
Example: Input BTU requirement of the water heater, 199,000 BTUH
Total pipe length, 50 feet = 7/8" IPS required.
10
206
348
536
5/8
3/4
7/8
20
141
239
368
30
n/a
192
296
40
n/a
164
253
50
n/a
146
224
60
n/a
132
203
80
n/a
n/a
174
100
n/a
n/a
154
125
n/a
n/a
137
1. For test pressures exceeding 1/2 psi (3.45 kPa) disconnect
the water heater and its Main Gas Shutoff Valve from the gas
supply piping system during testing, see Figure 37 on page
31. The gas supply line must be capped when disconnected
from the water heater.
2. For test pressures of 1/2 psi (3.45 kpa) or less, the water
heater need not be disconnected, but must be isolated from
the supply gas line by closing the Main Gas Shutoff Valve
during testing.
3. Paint all supply gas line joints and connections upstream of
the water heater with a rich soap and water solution to test
for leaks. Bubbles indicate a gas leak. Do not use matches,
candles, flame or other sources of ignition for this purpose.
4. Repair any leaks before placing the water heater in operation.
PURGING
Gas line purging is required with new piping or systems.
Purging should be performed per the current edition of NFPA 54
the National Fuel Gas Code or CAN/CSA B149.1 Natural Gas and
Propane Installation Code.
GAS LINE LEAK TESTING
Fire and Explosion Hazard
Leak test gas connections before
placing water heater in operation.
Disconnect gas piping at main
gas shutoff valve before leak
testing heater.
Install sediment trap in
accordance with NFPA 54 or
CAN/CSA B149.1.
Use joint compound or Teflon tape
compatible with propane gas.
Any time work is done on the gas supply system perform a leak test
to avoid the possibility of fire or explosion.