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Rinnai Tankless Water Heater Installation and Operation Manual 58
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 nd 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 22: 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 23: Pressure Drop 0.5 in. w.c.
Information in table
obtained from NFPA 54,
ANSI Z223.1 - 2015.
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
Specic Gravity: 0.60
Table 24: 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
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