Rinnai RH180, Installation Fundamentals

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Gas Supply Sizing Procedure
Point of Delivery
(gas meter) Outlet B
range/oven
75,000 Btu/hr
Outlet A
gas fireplace
30,000 Btu/hr
Outlet D
furnace
100,000 Btu/hr
Outlet C
RH180
91,300 Btu/hr
10 ft.
20 ft.
15 ft.
15 ft.
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.)
Nominal: ½ ¾ 1 1 ¼ 1 ½
Length
(ft) Capacity in Cubic Feet of Gas per Hour
(CFH=Btu/1000)
10 172 360 678 1390 2090
20 118 247 466 957 1430
30 95 199 376 768 1150
40 81 170 320 657 985
50 72 151 284 583 873
60 65 137 257 528 791
70 60 126 237 486 728
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
10 ft.
35
10 ft.
5 ft.
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.