A.O. Smith BTR 151 THRU 201/A - Manual (Page 9)

9
GAS PIPING
Contact your local gas service company to ensure that adequate
gas service is available and to review applicable installation
codes for your area.
Size the main gas line in accordance with Table 2. The figures
shown are for straight lengths of pipe at 0.5 in. W.C. pressure
drop, which is considered normal for low pressure systems.
Note: Fittings such as elbows, tees and line regulators will add
to the pipe pressure drop. Also refer to the latest version of the
National Fuel Gas Code.
WARNING
THE HEATER IS NOT INTENDED FOR OPERATION AT HIGHER
THAN 14.0" W.C.(3.48 kPa) - NATURAL GAS, 14.0" W.C.(3.48kPa)
EXPOSURE TO HIGHER SUPPLY PRESSURE MAY CAUSE
DAMAGE TO THE GAS VALVE 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.
TABLE 2 - GAS SUPPLY LINE SIZES (IN INCHES)*
MAXIMUM CAPACITY OF PIPE IN CUBIC FEET PER HOUR
(Based upon a Pressure Drop of 0.5 inch Water Column and
0.6 specific Gravity Gas and max. gas pressure of 0.5 psig)
LENGTH NOMINAL IRON PIPE SIZES (INCHES)
IN FEET 1/2" 3/4" 1" 1 1/4" 1 1/2" 2" 2 1/2" 3" 4"
10 175 360 680 1400 2100 3960 6300 11000 23000
20 120 250 465 950 1460 2750 4360 7700 15800
30 97 200 375 770 1180 2200 3520 6250 12800
40 82 170 320 660 990 1900 3000 5300 10900
50 73 151 285 580 900 1680 2650 4750 9700
60 66 138 260 530 810 1520 2400 4300 8800
70 61 125 240 490 750 1400 2250 3900 8100
80 57 118 220 460 690 1300 2050 3700 7500
90 53 110 205 430 650 1220 1950 3450 7200
100 50 103 195 400 620 1150 1850 3250 6700
125 44 93 175 360 550 1020 1650 2950 6000
150 40 84 160 325 500 950 1500 2650 5500
175 37 77 145 300 460 850 1370 2450 5000
200 35 72 135 280 430 800 1280 2280 4600
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 SEDIMENT TRAP OR
DRIP LEG) MUST BE INCORPORATED IN THE PIPING (SEE FIG.
9). THE DIRT LEG MUST BE READILY ACCESSIBLE AND NOT
SUBJECT TO FREEZING CONDITIONS. INSTALL IN
ACCORDANCE WITH RECOMMENDATIONS OF SERVING GAS
SUPPLIERS. REFER TO THE LATEST VERSION OF THE NATIONAL
FUEL GAS CODE.
To prevent damage, care must be taken not to apply too much
torque when attaching gas supply pipe to gas valve inlet.
Apply joint compounds (pipe dope) sparingly and only to the
male threads of pipe joints. Do not apply compounds to the first
two threads. Use compounds resistant to the action of liquefied
petroleum gases.
BEFORE PLACING THE HEATER IN OPERATION, CHECK FOR GAS
LEAKAGE.
Use soap and water solution or other material
acceptable for the purpose in locating the leaks. DO NOT USE
MATCHES, CANDLES, FLAME OR OTHER SOURCES OF IGNITION
FOR THIS PURPOSE.
DISCONNECT THE HEATER AND ITS MANUAL GAS SHUTOFF
VALVE FROM THE GAS SUPPLY PIPING SYSTEM DURING ANY
SUPPLY PRESSURE TESTING EXCEEDING 1/2 PSIG. GAS
SUPPLY LINE MUST BE CAPPED WHEN DISCONNECTED FROM
THE HEATER FOR TEST PRESSURES OF 1/2 PSIG OR LESS. THE
APPLIANCE NEED NOT BE DISCONNECTED, BUT MUST BE
ISOLATED FROM THE SUPPLY PRESSURE TEST BY CLOSING
THE MANUAL GAS SHUTOFF VALVE.
GAS PIPING AND DIRT LEG INSTALLATION
FIGURE 9
PURGING
Gas line purging is required with new piping or systems in which
air has entered.
CAUTION
PURGING SHOULD BE PERFORMED BY PERSONS EXPERIENCED
IN THIS TYPE GAS SERVICE. TO AVOID RISK OF FIRE OR
EXPLOSION, PURGE DISCHARGE MUST NOT ENTER CONFINED
AREAS OR SPACES WHERE IGNITION CAN OCCUR. THE AREA
MUST BE WELL VENTILATED AND ALL SOURCES OF IGNITION
MUST BE INACTIVATED OR REMOVED.
GAS METER SIZE — NATURAL GASES ONLY
Be sure 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 gas
meter is too small, ask the gas company to install a larger meter
having adequate capacity.
GAS PRESSURE REGULATOR
The gas pressure regulator is built into the gas valve and is
equipped to operate on the gas specified on model and rating
plate. The regulator is factory adjusted to deliver gas to burner at
correct water column pressure allowing for a nominal pressure
drop through the controls.
The minimum gas supply pressure for input adjustment must
not be less than 4.5" w.c. for natural gas.