John Wood Commercial - AJWSC - Manual (Page 8)

Note: If using a flexible gas connector, make sure its rating
tag matches or exceeds the input of the water heater.
Tables 1, 2, and 3 provide a sizing reference for commonly
used gas pipe materials. Consult the “Natural Gas and
Propane Installation Code” or “National Fuel Gas Code”
for the recommended gas pipe size of other materials.
Follow the instructions below and reference Figure 3 for gas
piping installation.
Note: When installing gas piping, apply sealing compounds
approved for use with natural and propane gas.
1. Install a readily accessible manual shut-off valve in the
gas supply line as recommended by the local utility. The
owner/operator must be shown the location of this valve
and be given instructions on how to use it to shut off the
gas to the heater.
2. Install a drip leg (if not already incorporated as part of
the water heater) as shown. The drip leg must be no
less than 76mm (3 in.) long for the accumulation of dirt,
foreign material, and water droplets.
3. Install a ground joint union between the gas valve and
the manual shut-off valve. This is to allow easy removal
of the gas valve.
4. Turn the gas supply on and check for leaks. Use a chlo-
ride-free soap and water solution (bubbles forming indi-
cate a leak) or other approved method.
Gas Pressure
Important: The gas supply pressure must not exceed the
maximum supply pressure as stated on the water heater’s
data plate. Minimum supply pressure should also be main-
tained per the data plate.
L.P. Gas Capacity
Size, (in) 10 20 30 40 50 60 70 80 90 100 125 150
1/2 275 189 152 n/a n/a n/a n/a n/a n/a n/a n/a n/a
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
Maximum capacity of gas pipe in thousands of BTU per hour of undiluted liquified petroleum gasses (at 11 inches
water column pressure). Based on a Pressure Drop of 0.5 Inch Water Column.
Nominal Iron Pipe
Length of pipe, Feet
Example: Input BTU requirements of the water heater, 199,000 BTUH
Total pipe length, 80 feet - 1" IPS required.
L.P. Gas Capacity
Size, (in) 10 20 30 40 50 60 80 100 125
5/8 206 141 n/a n/a n/a n/a n/a n/a n/a
3/4 348 239 192 164 146 132 n/a n/a n/a
7/8 536 368 296 253 224 203 174 154 137
Maximum capacity of gas pipe in thousands of BTU per hour of undiluted liquified petroleum gasses (at 11 inches
water column pressure). Based on a Pressure Drop of 0.5 Inch Water Column.
Copper Tubing OD
Example: Input BTU requirements of the water heater, 199,000 BTUH
Total pipe length, 50 feet = 7/8" IPS required.
Length of pipe, Feet
Natural Gas Pipe Capacity (Cu. ft./hr)
Size, in. 10 20 30 40 50 60 70 80 90 100 125 150 175 200
1/2 132 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a
3/4 278 190 152 130 115 105 96 n/a n/a n/a n/a n/a n/a n/a
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
Cu. Ft. Per Hr. Required =
Gas Input of Water Heater (BTU/HR)
Heating Value of Gas (BTU/FT
3 )
The gas input of the water heater is marked on the water heater data plate. The heating value of the gas (BTU/ft 3 ) may
be determined by consulting the local natural gas utility.
Capacity of gas pipe of different diameters and lengths in cu. ft. per hr. with pressure drop of 0.3 in. and specific
gravity of 0.60 (natural gas).
Nominal Iron Pipe
Length of Pipe, Feet
After the length of pipe has been determined, select the pipe size which will provide the maximum cubic feet per hour
required for the gas input rating of the water heater. By formula:
Table 1
Table 2
Table 3
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