Gas Meter Size; Gas Piping; Gas Pressure Regulation; Gas Valves - A.O. Smith 650A, 740A Installation & Operation Manual

TABLE 9A
MAXIMUM CAPACITY OF PIPE IN CUBIC FEET OF GAS PER HOUR
(Based upon a Pressure Drop of 0.5 inch Water Column
and 0.5 Specific Gravity Gas and max. gas press. of .5 psig)
LENGTH
IN Nominal Iron Pipe Sizes, Millimeters
METERS 1/2" 3/4" 1" 1 1/4" 1 1/2"
3.0 51 105 199 410
6.1 35 73 142 278
9.1 28 59 110 225
12.2 24 50 94 193
15.2 21 44 83 170
18.3 19 40 76 155
21.3 18 37 70 143
24.4 17 35 64 135
27.4 16 32 60 126
30.5 15 30 57 117
38.1 13 27 51 105
45.7 12 25 47 95
53.3 11 23 42 88
61.0 10 21 40 82
THE HEATER IS NOT INTENDED FOR OPERATION AT HIGHER
THAN 14" (3.5 kPa) WATER COLUMN (1/2 POUND PER SQUARE
INCH) SUPPLY GAS PRESSURE. HIGHER GAS PRESSURES
REQUIRE SUPPLEMENTAL REDUCING SERVICE REGULATION.
EXPOSURE TO HIGHER GAS SUPPLY PRESSURE MAY CAUSE
DAMAGE TO THE GAS CONTROLS WHICH COULD RESULT IN
FIRE OR EXPLOSION. IF OVERPRESSURE HAS OCCURRED
SUCH AS THROUGH IMPROPER TESTING OF GAS LINES OR
EMERGENCY MALFUNCTION OF THE SUPPLY SYSTEM, THE GAS
VALVE MUST BE CHECKED FOR SAFE OPERATION. MAKE SURE
THAT THE OUTSIDE VENTS ON THE SUPPLY REGULATORS AND
THE SAFETY VENT VALVES ARE PROTECTED AGAINST
BLOCKAGE. THESE ARE PARTS OF THE GAS SUPPLY SYSTEM,
NOT THE HEATER. VENT BLOCKAGE MAY OCCUR DURING ICE
STORMS.
IT IS IMPORTANT TO GUARD AGAINST GAS VALVE FOULING
FROM CONTAMINANTS IN THE GAS WAYS. SUCH FOULING MAY
CAUSE IMPROPER OPERATION, FIRE OR EXPLOSION.
IF COPPER SUPPLY LINES ARE USED THEY MUST BE
INTERNALLY TINNED AND CERTIFIED FOR GAS SERVICE.
BEFORE ATTACHING THE GAS LINE, BE SURE THAT ALL GAS
PIPE IS CLEAN ON THE INSIDE.
TO TRAP ANY DIRT OR FOREIGN MATERIAL IN THE GAS SUPPLY
LINE, A DIRT LEG (SOMETIMES CALLED A SEDIMENT TRAP OR
DRIP LEG) MUST BE INCORPORATED IN THE PIPING (SEE FIG.
10) THE DIRT LEG MUST BE READILY ACCESSIBLE AND NOT
SUBJECT TO FREEZING CONDITIONS.
ACCORDANCE WITH RECOMMENDATIONS OF SERVING GAS
SUPPLIERS. REFER TO THE NATIONAL FUEL GAS CODE.
To prevent damage, care must be taken not to apply too much
torque when attaching gas supply to gas valve inlet.
Apply joint compounds (pipe dope) sparingly and only to the
male threads of pipe joints. Do not apply compound to the first
two threads. Use compounds resistant to the action of liquefied
petroleum gases.
DISCONNECT THE APPLIANCE AND ITS MANUAL GAS SHUT-
OFF VALVE FROM THE GAS SUPPLY PIPING SYSTEM DURING
2" 2 1/2" 3"
615 1160 1845 3221
428 805 1277 2255
346 644 1031 1830
290 556 878 1552
264 492 776 1391
237 445 703 1259
220 410 659 1142
202 381 600 1083
190 357 571 1010
182 337 542 952
161 299 483 864
146 278 439 776
135 249 401 717
126 234 375 688
WARNING
INSTALL IN
ANY SUPPLY PRESSURE TESTING EXCEEDING 1/2 PSIG. GAS
SUPPLY LINE MUST BE CAPPED WHEN DISCONNECTED
FROM THE HEATER. FOR TEST PRESSURES OF ½ PSIG OR
LESS, THE APPLIANCE NEED NOT BE DISCONNECTED, BUT
MUST BE ISOLATED FROM THE SUPPLY PRESSURE TEST BY
CLOSING THE MANUAL GAS SHUT-OFF VALVE.
4"
6735
4626
3748
3192
2840
2577
2372
2196
2108
1962
1757
1610
1464
1347
GAS PIPING AND DIRT LEG INSTALLATION
BEFORE PLACING THE HEATER IN OPERATION, CHECK FOR GAS
LEAKAGE. USE SOAP AND WATER SOLUTION OR OTHER
MATERIAL ACCEPTABLE FOR THE PURPOSE IN LOCATING
GAS LEAKS. DO NOT USE MATCHES, CANDLES, FLAME OR
OTHER SOURCES OF IGNITION FOR THIS PURPOSE.
GAS METER SIZE – CITY GASES ONLY
Be sure that the gas meter has sufficient capacity to supply the
full rated gas input of the water heater as well as the requirements
of all other gas fired equipment supplied by the meter. If the gas
meter is too small, request the gas company to install a larger
meter having adequate capacity.

GAS PRESSURE REGULATION

Main line gas pressure to the water heater should be between
8" w.c. (2 kPa) minimum (dynamic pressure or net pressure)
and 14" (3.5 kPa) maximum w.c. (static pressure). The inlet gas
pressure must not exceed the maximum value. A service
regulator is necessary if higher gas pressures are encountered,
see Table 10.
Due to pressure drop along gas supply line, to maintain
8" w.c. (2 kPa) minimum dynamic pressure, initial gas inlet
pressure must be set at higher than 8" w.c. (2 kPa). The gas
regulator must be properly sized to prevent unstable control or
excessive pressure drop.
Figure 10 shows the gas control valve that is supplied on these
heaters.
12
FIGURE 9.

GAS VALVES