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4.8.2 Gas Pipe Sizing Reference Tables
The gas supply must be capable of handling the entire gas
load required at the location. Gas line sizing is based on
gas type, the pressure drop in the system, the gas pressure
supplied, and gas line type. For gas pipe sizing, refer to the
National Fuel Gas Code, ANSI Z223.1/NFPA 54.
For some tables, you will need to determine the cubic
feet per hour of gas required by dividing the gas input by
the heating value of the gas (available from the local gas
company). The gas input needs to include all gas products
at the location and the maximum Btu usage at full load
when all gas products are in use.
Use the table for your gas type and pipe type to find the
pipe size required. The pipe size must be able to provide
the required cubic feet per hour of gas or the required Btu/
hour.
The information below is provided as an example. The
appropriate table from the applicable code must be used.
Natural Gas
Table 14: Pressure Drop 0.3 in. wc
Information in table
obtained from NFPA 54,
ANSI Z223.1
3/4
Length in ft
Capacity in Cubic Feet of Gas per Hour
(meters)
10 (3)
273
20 (6)
188
30 (9)
151
40 (12)
129
50 (15)
114
60 (18)
104
70 (21)
95
80 (24)
89
90 (27)
83
100 (30)
79
Rinnai Tankless Water Heater Installation and Operation Manual
Schedule 40 Metallic Pipe
Inlet Pressure:
Less than 2 psi
Specific Gravity:
Nominal Pipe Size (in.)
1
1 1/4
514
1,060
353
726
284
583
243
499
215
442
195
400
179
368
167
343
157
322
148
304
Table 13: Gas Pipe Sizing Calculation
Worksheet
Instructions: Enter values in empty boxes.
Rinnai Model Gas Input:
Additional Appliance Total Gas Input:
Heating Value of Gas:
Cubic Feet Per Hour (CFH):
Answer:
Rinnai Model Gas Input:
A
0.60
Additional Appliance Total Gas Input:
B
1 1/2
Heating Value of Gas:
C
Cubic Feet Per Hour (CFH):
1,580
1,090
(CFH)
873
747
(CFH) =
662
Answer:
600
552
(CFH) =
514
For this example, the pipe diameter
must be at least 3/4 in. pipe size and 10
482
ft (3 m) in length.
455
A
B
C
A + B
(CFH) =
C
(CFH) =
(CFH) =
Table 15: Example
199,000
Btu/hr
65,000
Btu/hr
1,000
Btu/ft
3
A
+
B
=
C
199,000+65,000
1,000
264
35
Btu/hr
Btu/hr
Btu/ft
3
ft
/hr
3
ft
/hr
3
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