A.O. Smith 400A - Manual (Page 15)

5
CAUTION
THE WATER HEATER IS POLARITY SENSITIVE. BEFORE
APPLYING ELECTRICITY TO THIS HEATER BE CERTAIN THAT
SUPPLY NEUTRAL WIRE TO GROUND CHECK INDICATES ZERO
VOLTAGE.
HOT SURFACE IGNITER
The Hot Surface Igniter is a device that ignites the main burner by
high temperature (>1800°F or >982°C). When 120VAC is applied
to the igniter, sufficient heat is generated to ignite the main burner.
Although improvements have been made to strengthen the igniter,
it is fragile and care must be taken when handling the igniter to
prevent breakage.
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 3. The figures
shown are for straight lengths of pipe at 0.5 in. W.C. (125Pa)
pressure drop, which is considered normal for low pressure
systems Note that fittings such as elbows and tees will add to the
pipe pressure drop.
CAUTION
DO NOT USE FLEXIBLE GAS PIPING.
TABLE 3. MAXIMUM CAPACITY OF PIPE IN CUBIC FEET OF GAS
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).
WARNING
THE HEATER IS NOT INTENDED FOR OPERATION AT HIGHER
THAN 11.0" WATER COLUMN (2.74 Kpa) FOR NATURAL GAS AND
14.0" W.C. (3.49kPa) FOR PROPANE GAS SUPPLY PRESSURE.
HIGHER GAS SUPPLY 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. 14). 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 NATIONAL FUEL GAS CODE NFPA
54 OR THE NATURAL GAS AND PROPANE INSTALLATION
CODE CAN/CSA-B149.1.
FIGURE 14.
CONNECTION OF GAS PIPE
1. When connecting gas pipe to unit, apply wrench to flange only.
Note: Do not use wrench on gas valve or gas bracket.
2. PERFORM THE GAS LEAK TEST ANY TIME WORK IS DONE
ON A GAS SYSTEM TO AVOID THE POSSIBILITY OF FIRE OR
EXPLOSION WITH PROPERTY DAMAGE, PERSONAL INJURY
OR LOSS OF LIFE.
The Gas Leak Test is performed as follows: Paint pipe connections
upstream of gas control with a rich soap and water solution to test
for leaks before operating main burner. Bubbles indicate gas leak.
To stop leak, tighten pipe connections. After piping connections are
checked, turn on main burner. With main burner in operation, paint
pipe joints (including flanges), pilot gas tubing connections and
control inlet and outlet with rich soap and water solution. Bubbles
indicate gas leak. To stop leak, tighten flange screws, joints and pipe
connections. Replace part if leak can’t be stopped.
LENGTH NORMAL IRON PIPE SIZES (INCHES)
IN INPUT IN THOUSANDS BTU/HR
FEET 1 1/4" 1 1/2" 2" 2 1/2" 3" 4"
10 1400 2100 3960 6300 11000 23000
20 950 1460 2750 4360 7700 15800
30 770 1180 2200 3520 6250 12800
40 660 990 1900 3000 5300 10900
50 580 900 1680 2650 4750 9700
60 530 810 1520 2400 4300 8800
70 490 750 1400 2250 3900 8100
80 460 690 1300 2050 3700 7500
90 430 650 1220 1950 3450 7200
100 400 620 1150 1850 3250 6700
125 360 550 1020 1650 2950 6000
150 325 500 950 1500 2650 5500
175 300 460 850 1370 2450 5000
200 430 800 1280 2280 4600
LENGTH NORMAL IRON PIPE SIZES (INCHES)
IN INPUT IN KW
METERS 1 1/4" 1 1/2" 2" 2 1/2" 3" 4"
3.0 410 615 1160 1845 3221 6735
6.1 278 428 805 1277 2255 4626
9.1 225 346 644 1031 1830 3748
12.2 193 290 556 878 1552 3192
15.2 170 264 492 776 1391 2840
18.3 155 237 445 703 1259 2577
21.3 143 220 410 659 1142 2372
24.4 135 202 381 600 1083 2196
27.4 126 190 357 571 1010 2108
30.5 117 182 337 542 952 1962
38.1 105 161 299 483 864 1757
45.7 95 146 278 439 776 1610
53.3 88 135 249 401 717 1464
61.0 126 234 375 688 1347