Smith Cast Iron Boilers GB250 SERIES - Manual (Page 10)

10
STEP 5: INSTALLING & TESTING GAS PIPING
Connect the gas piping from the meter to the boiler
using a pipe size which will result in a pressure drop of
less than 0.3" W.C. for natural gas or 0.5" W.C. for
propane. See Figure 2.10 for the appropriate gas pipe
sizing and example.
Good piping practices should be followed at all times.
See Figure 2.11 for a typical gas piping arrangement. All
piping must be supported by hangers, not by the boiler
or its accessories.
Install a full-sized sediment trap at the low point in gas
line upstream of gas valve. Install a non-restrictive
lubricated plug valve in the gas line close to the boiler.
Install a ground joint union at the gas valve inlet to allow
for servicing. Check local codes and utilities for any
special requirements and procedures.
Pipe joint compound (pipe dope) must be compatible
with the fuel (natural gas or propane) being used.
Maximum Capacity of Pipe in Cubic Feet of Natural Gas per Hour for Gas Pressures of
0.5 Psig or Less and a Pressure Drop of 0.3 Inch Water Column
(Based on a 0.60 Specific Gravity Gas)
Nominal
Iron Pipe
Size,
Inches
Internal
Diameter,
Inches
Length of Pipe, Feet
10
32
72
132
278
520
1,050
1,600
3,050
4,800
8,500
17,500
20
22
49
92
190
350
730
1,100
2,100
3,300
5,900
12,000
30
18
40
73
152
285
590
890
1,650
2,700
4,700
9,700
40
15
34
63
130
245
500
760
1,450
2,300
4,100
8,300
50
14
30
56
115
215
440
670
1,270
2,000
3,600
7,400
60
12
27
50
105
195
400
600
1,150
1,850
3,250
6,800
70
11
25
46
96
180
370
560
1,500
1,700
3,000
6,200
80
11
23
43
90
170
350
530
990
1,600
2,800
5,800
90
10
22
40
84
160
320
490
930
1,500
2,600
5,400
100
9
21
38
79
150
305
460
870
1,400
2,500
5,100
125
8
18
34
72
130
275
410
780
1,250
2,200
4,500
150
8
17
31
64
120
250
380
710
1,130
2,000
4,100
175
7
15
28
59
110
225
350
650
1,050
1,850
3,800
200
6
14
26
55
100
210
320
610
980
1,700
3,500
1/4"
3/8"
1/2"
3/4"
1"
1-1/4"
1-1/2"
2"
2-1/2"
3"
4"
.326
.493
.622
.824
1.049
1.380
1.610
2.067
2.469
3.026
4.026
Maximum Capacity of Pipe in Thousands of Btu per Hour of Undiluted Liquefied
Petroleum Gases (at 11 Inches Water Column Inlet Pressure)
(Based on a Pressure Drop of 0.5 Inch Water Column)
Nominal
Iron Pipe
Size,
Inches
Length of Pipe, Feet
10
275
567
1071
2205
3307
6221
20
189
393
732
1496
2299
4331
30
152
315
590
1212
1858
3465
40
129
267
504
1039
1559
2992
50
114
237
448
937
1417
2646
60
103
217
409
834
1275
2394
70
96
196
378
771
1180
2205
80
89
185
346
724
1086
2047
90
83
173
322
677
1023
1921
100
78
162
307
630
967
1811
125
69
146
275
567
866
1606
150
63
132
252
511
787
1498
1/2"
3/4"
1"
1-1/4"
1-1/2"
2"
FIGURE 2.10
Example: Boiler Model GB250-7 is to be installed. The distance from the existing gas meter installation site is 20 feet. What
pipe size must be used? The local utility indicates the heating value of the natural gas being supplied is 1,000 Btu per cubic
foot. Determine the cubic feet of gas per hour for above boiler model:
300,000 Btu per hour
= 300 cu. ft. per hour
1,000 Btu per cu. ft.
1. Find 20 ft. in the upper portion of the table for natural gas under Length of Pipe, Feet heading.
2. Moving down the column, match the required capacity. The higher capacity is acceptable. In our case, it is 350 cu. ft.
3. Move to the left-hand column Nominal Iron Pipe Size, Inches to read required pipe size. In our case, it is 1".