Gas System - Rinnai RH180 Installation Fundamentals

Gas System

If resizing gas supply lines is not a feasible option, a two stage supply system may be used depending on
local code guidelines. Two stage systems operate in the following manner:
• Higher pressure (usually 2 lbs or approximately
56" w.c.) is supplied for a large portion of the
supply system.
• By increasing the system pressure, this
overcomes volume inadequacies. NOTE: Never
apply high pressure (such as 2 lbs) to a
household appliance unless stated by the
manufacturer. All Rinnai tankless water heaters
require no more than ½" lb inlet pressure (14"
w.c.).
• Regulators are placed close to each appliance to
reduce pressure to the appliance standard of ½
lb or approximately 7-14" w.c.
• Follow NFPA 54 guideline and all code
requirements when sizing two stage systems.
• Two stage systems can be used in NG or LP
applications—sizing values differ by gas type
• Gas meter capacity must also be considered
37
Two stage piping example
–
The below example has the following parameters
Gas: NG
Outlet C
RH180
91,300 Btu/hr
Main gas meter
supplies 2 lbs of
pressure through
existing pipes
Outlet B
Point of Delivery
range/oven
(gas meter)
75,000 Btu/hr
Inlet pressure: 2 PSI
Outlet D
furnace
100,000 Btu/hr
Regulators are placed in
close vicinity to all appliances
bringing pressure to appliance
standard (1/4-1/2 lb)
Outlet A
gas fireplace
30,000 Btu/hr