A.O. Smith HW 300 Instruction Manual page 19

GAS CONNECTIONS
Make sure the gas on which boiler is to operate is same as that
specified on the rating plate. Do not install boiler if equipped for
a different type of gas. Consult your gas supplier.
This boiler is not intended to operate at gas supply pressure
other than shown on the rating plate. A lock-up or positive shut-
off type regulator must be installed in gas supply line. For proper
gas regulation the lock-up style regulators must be installed no
closer than a minimum of 3 feet from the boiler and a maximum
of 8 feet away from the boiler. Exposure to higher gas supply
pressure may cause damage to gas control valves which can
result in fire or explosion. If overpressure has occurred such as
through improper testing of gas lines or emergency malfunction
of supply system, the gas control valves must be checked for safe
operation. Make sure that the outside vents on supply regulators
and the safety vent valves are protected against blockage. These
are parts of the gas supply system, not boiler. Vent blockage may
occur during ice build-up or snowstorms.
The boiler must be isolated from the gas supply piping system by
closing its main manual gas shut off valve during any pressure
testing of the gas supply piping system at test pressures equal
to or less than 1/2 psig.
Disconnect the boiler and its main manual gas shut-off valve
from the gas supply piping during any pressure testing of the gas
supply system over 1/2 psig. The gas supply line must be capped
when not connected to the boiler.
It is important to guard against gas control 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 approved for gas service.
When local codes require a main manual shut-off valve outside
the boiler jacket, a suitable main manual shut-off valve must be
installed in a location complying with those codes.
Before attaching gas line be sure that all gas pipe is clean
on inside. To trap any dirt or foreign material in the gas supply
line, a sediment trap must be incorporated in piping. The
sediment trap must be readily accessible and not subject to
freezing conditions. Install in accordance with recommendations
of serving gas supplier. Refer to the current edition of the National
Fuel Gas Code, ANSI Z223.1/NFPA 54 or the Natural Gas and
Propane Installation Code, CAN/CSA B149.1
Size of gas supply piping may be larger than heater connection
on installations where a significant run of piping is required.
To prevent damage, care must be taken not to apply too much
torque when attaching gas supply pipe to boiler gas inlet. When
installing and tightening gas piping use a second wrench to hold
the gas control valve to keep the valve from turning. To prevent
damage to the gas control valve do not use pipe wrench on the
valve body.
Fittings and unions in gas line must be of metal to metal type.
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. The boiler and its gas connection must be leak
tested before placing the boiler in operation.
SIZING GAS SUPPLY
INSTALLATIONS AND FOR INSTALLATIONS OF MULTIPLES
OF TWO OR THREE OF SAME SIZE BOILERS).
Use Table 11 or CAN/CSA B149.1 (current edition) to size
iron pipe or equivalent gas supply line. Table 11 is based on a
pressure drop of 0.3 inches of water and a specific gravity of 0.60
approximately that of natural gas. (Propane (LP) gas has an S.G.
of about 1.53). If the service pressure is five inches water column
or less, use one pipe size larger in order to minimize pressure
drop in the line.
MAxIMUM CAPACITY OF PIPE IN CUBIC FEET OF GAS
PER HOUR (BASED UPON A PRESSURE DROP OF 0.3
INCH WATER COLUMN AND 0.6 SPECIFIC GRAVITY GAS)
Distance
Nominal Iron Pipe Size (Inches)
from Gas
Meter
1/2 3/4 1
10 (3) 132 278 520 1,050 1,600 3,050 4,800 8,500 17,500
20 (6) 92 190 350
30 (9) 73 152 285
40(12) 63 130 245
50 (15) 56 115 215
60 (18) 50 105 195
70 (21) 46 96 180
80 (24) 43 90 170
90 (27) 40 84 160
100 (30) 38 79 150
125 (38) 34 72 130
150 (45) 31 64 120
175 (53) 28 59 110
200 (60) 26 55 100
*The heating value of Natural Gas is approximately 1,050 Btu/Ft
Propane (LP) Gas has a heating value of approximately 2,500 Btu/Ft
1 cu. meter=35.31 cu. feet.
Where it is necessary to use more than the average number of
pipe fittings i.e. elbows, tees, and valves in gas supply line, use a
pipe larger than specified to compensate for increased pressure
drop.
19
LINE (FOR SINGLE
TABLE 11.
1 1/4 1 1/2 2 2 1/2 3
730 1,100 2,100 3,300 5,900 12,000
590 890 1,650 2,700 4,700 9,700
500 760 1,450 2,300 4,100 8,300
440 670 1,270 2,000 3,600 7,400
400 610 1,150 1,850 3,250 6,800
370 560 1,050 1,700 3,000 6,200
350 530 990 1,600 2,800 5,800
320 490 930 1,500 2,600 5,400
305 460 870 1,400 2,500 5,100
275 410 780 1,250 2,200 4,500
250 380 710 1,130 2,000 4,100
225 350 650 1,050 1,850 3,800
210 320 610 980 1,700 3,500
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BOILER
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