A.O. Smith 100 Series Installation And Operating Manual page 36

4. Install a ground union between the water heater and the manual
shut-off valve. This is to allow easy servicing. See Figure 47.
Turn the gas supply on and check for leaks. See Figure 47 . Use a
5.
chloride-free soap and water solution (bubbles forming indicate
a leak) or other approved method.
Note: Units with inputs of 175,000 BTU/hr or above must have a
minimum of 3/4" NPT gas pipe supplied to the water heater.
BLACK PIPE
INSTALLATIONS
SEDIMENT
3" MIN.
TRAP
CAP
Figure 41. Black Pipe to Gas Valve
Note: Always secure the square on the gas valve base with a
suitable wrench when tightening or loosening the gas piping.
GAS LINE SIZING
Depending on the developed equivalent length and/or the number
of appliances connected to a common main, the size of supply gas
lines may have to be increased.
Size the supply/main gas line(s) in accordance with Table 18 or Table 19.
The values given in Table 18 or Table 19 are for straight lengths of
iron pipe at 0.5" W. C. (125 Pa) pressure drop, which is considered
normal for low pressure systems.
Note: Fittings such as elbows and tees will add to the pipe pressure
drop.
Schedule-40 Steel or wrought-iron pipe is the preferred material for
the gas line of this water heater. It is imperative to follow the sizing
recommendations in the latest version of the National Fuel Gas Code
if corrugated stainless steel tubing (CSST) is used as the gas line
for this water heater.
GAS
CONTROL
VALVE
GROUND
JOINT UNION
(OPTIONAL)
Table 18. Supply Gas Line Sizing U. S. Units
Normal Iron Pipe Sizes (Inches)
Length in
Feet
1/2"
10
175
20 120
30 97
40
82
50 73
60 66
70
61
80 57
90 53
100 50
125 44
150 40
175 37
200 35
Table 19. Supply Gas Line Sizing Metric Units
Normal Iron Pipe Sizes (inches)
Length In
Meters 1/2" 3/4"
3.0 51
6.1 35
9.1 28
12.2
24
15.2 21
18.3 19
21.3
18
24.4 17
27.4 16
30.5
15
38.1 13
45.7 12
53.3
11
61.0 10
36
Input In Thousands Btu/Hr
3/4" 1" 1 1/4" 1 1/2"
360 680 1400 2100
250 485 950 1460
200 375 770 1180
170 320 660 990
151 285 580 900
138 260 530 810
125 240 490 750
118 220 460 690
110 205 430 650
103 195 400 620
93 175 360 550
84 160 325 500
77 145 300 460
72 135 280 430
Input in kW
1" 1 1/4" 1 1/2"
105 199 410 615
73 142 278 428
59 110 225 346
50 94 193 290
44 83 170 264
40 76 155 237
37 70 143 220
35 64 135 202
32 60 126 190
30 57 117 182
27 51 105 161
25 47 95 146
23 42 88 135
21 40 82 126
2"
3960
2750
2200
1900
1680
1520
1400
1300
1220
1150
1020
950
850
800
2"
1160
805
644
556
492
445
410
381
357
337
299
278
249
234