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Rinnai Tankless Water Heater Installation and Operation Manual
4.10.2 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, or the Natural Gas and Propane
Installation Code, CSA B149.1
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.
Table 23: 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:
A
Btu/hr
B
Btu/hr
C
Btu/ft
3
(CFH)
=
A + B
C
(CFH)
=
(CFH)
=
ft
3
/hr
Natural Gas
Table 24: Pressure Drop 0.5 in. wc
Information in table
obtained from NFPA 54,
ANSI Z223.1 - 2021.
Nominal Pipe Size (in.)
1/2
3/4
1
1 1/4
Length in ft (meters)
Capacity in Cubic Feet of Gas per Hour
10 (3)
172
360
678
1,390
20 (6)
118
247
466
957
30 (9)
95
199
374
768
40 (12)
81
170
320
657
50 (15)
72
151
284
583
60 (18)
65
137
257
528
70 (21)
60
126
237
486
80 (24)
56
117
220
452
90 (27)
52
110
207
424
100 (30)
50
104
195
400
Schedule 40 Metallic Pipe
Inlet Pressure:
Less than 2 psi
Specific Gravity:
0.60
Table 25: Example
Rinnai Model Gas Input:
Additional Appliance Total Gas Input:
Heating Value of Gas:
Cubic Feet Per Hour (CFH):
Answer:
For this example, the pipe diameter
must be at least 3/4 in. pipe size and
10 ft (3 m) in length.
A
199,000
Btu/hr
B
65,000
Btu/hr
C
1,000
Btu/ft
3
(CFH)
=
A + B
C
(CFH)
=
199,000+65,000
1,000
(CFH)
=
264
ft
3
/hr
