Rinnai RH180 Installation Fundamentals page 35

Gas Supply Sizing Procedure
This gas supply sizing procedure is known as the longest length method. This example is for Natural gas. A full
explanation of NG and LPG pipe sizing can be found in the National Fuel Gas Code Manual
1. Using this method you first
determine the total pipe length from
the gas meter to the appliance farthest
from the meter. (60 ft. in this example)
2. Once this length is determined find
the line on the appropriate table in the
NFPA 54 manual that corresponds to
that length (for your pipe, type of gas,
inlet pressure and specific gravity).
3. The 60 ft. measurement will be the
only length used for this calculation.
10 ft.
Point of Delivery
(gas meter)
35
Outlet C
RH180
91,300 Btu/hr
10 ft.
20 ft.
10 ft.
range/oven
75,000 Btu/hr
Outlet D
furnace
100,000 Btu/hr
Nominal:
Length
(ft)
10
20
30
40
50
15 ft.
60
70
15 ft.
Outlet B
Schedule 40 Metallic Pipe, Natural Gas, less than 2 psi inlet
pressure, 0.5" w.c. pressure drop, 0.60 specific gravity.
Pipe Size (in.)
½ ¾ 1
Capacity in Cubic Feet of Gas per Hour
(CFH=Btu/1000)
172 360 678
118 247 466
95 199 376
81 170 320
72 151 284
65 137 257
60 126 237
5 ft.
1 ¼ 1 ½
1390 2090
957 1430
768 1150
657 985
583 873
528 791
486 728
Outlet A
gas fireplace
30,000 Btu/hr