Rinnai Tankless Water Heater Installation and Operation Manual
35
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.
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:
A
Btu/hr
B
Btu/hr
C
Btu/ft
3
(CFH)
=
A + B
C
(CFH)
=
(CFH)
=
ft
3
/hr
Natural Gas
Table 14: Pressure Drop 0.3 in. wc
Information in table
obtained from NFPA 54,
ANSI Z223.1
Nominal Pipe Size (in.)
3/4
1
1 1/4
1 1/2
Length in ft
(meters)
Capacity in Cubic Feet of Gas per Hour
10 (3)
273
514
1,060
1,580
20 (6)
188
353
726
1,090
30 (9)
151
284
583
873
40 (12)
129
243
499
747
50 (15)
114
215
442
662
60 (18)
104
195
400
600
70 (21)
95
179
368
552
80 (24)
89
167
343
514
90 (27)
83
157
322
482
100 (30)
79
148
304
455
Schedule 40 Metallic Pipe
Inlet Pressure:
Less than 2 psi
Specific Gravity:
0.60
Table 15: 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
