A.O. Smith Water Heater - Manual (Page 10)

LP Gas Only
AWARNING
U/
Explosion Hazard
Have a qualified person make sure L.P. gas pressure
does not exceed 13” water column.
Examples of a qualified person inciude: licensed
plumbers, authorized gas company personnei, and
authorized service personnei.
Faiiure to do so can resuit in death, expiosion, or fire.
Liquefied petroleum gas is over 50% heavier than air
and in the occurrence of a leak in the system, the gas
will settle at floor level. Basements, crawl spaces, closets
and areas below ground level will serve as pockets for
the accumulation of gas. Before lighting an L.P. gas water
heater, smell all around the appliance at floor level. If you
smell gas, follow the instructions as given in the warning
on the front page.
When your L.P. tank runs out of fuel, turn off the gas at
all gas appliances including pilot lights. After the tank is
refiiled, all appliances must be re-lit according to their
manufacturer’s instructions.
Table 1
Natural Gas Pipe Capacity Table (Cu. Ft./Hr.)
Capacity of gas pipe of different diameters and lengths in cu.
of 0.60 (natural gas). ft. per hr. with pressure drop of 0.3 in. and specific gravity
Nominal Iron Pipe Length of Pipe, Feet
Size, in. 10 20 30 40 50 60 70 80 90 100 125 150 175 200
1/2 132 92 73 63 56 50 46 43 40 38 34 31 28 26
3/4 278 190 152 130 115 105 96 90 84 79 72 64 59 55
1 520 350 285 245 215 195 180 170 160 150 130 120 110 100
1-1/4 1050 730 590 500 440 400 370 350 320 305 275 250 225 210
1-1/2 1600 1100 890 760 670 610 560 530 490 460 410 380 350 320
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:
r» c* D Lj D
- A
Gas Input of Water Heater (BTU/HR)
Cu. Ft. Per Hr. Required= —□—
t -—m
----------- rF—
Heating Value of Gas (BTU/FP)
The gas input of the water heater is marked on the water heater data plate. The heating value of the gas (BTU/FT)
may be determined by consulting the local natural gas utility.
Table 2
LP Gas Capacity Table
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.
Nominal Iron Pipe
Size, in. in
Length of Pipe, Feet
M. M.
1/2 275 189 152 129 114 103 96 89 83 78 69 63
3/4 576 393 315 267 237 217 196 185 173 162 146 132
1 1071 732 590 504 448 409 378 346 322 307 275 252
1-1/4 2205 1496 1212 1039 913 834 771 724 677 630 567 511
Example: Input BTU requirement of the water heater 100,000 BTUH.
Total pipe length, 80 feet = 3/4" IPS required.
Additional tables are available in the latest edition of the "National Fuel Gas Code", ANSI Z223.1.
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