AAON RN-140 - Manual (Page 54)

54
Do not use gas piping smaller than unit gas
connections. Natural gas pipe runs longer
than 20 feet and propane gas pipe runs
longer than 50 feet may require a larger
supply pipe than the unit connection size.
Some utility companies may also require
pipe sizes larger than the minimum sizes
listed.
Piping Sizing Examples
A 100 ft pipe run is needed for a 1080 MBH
natural gas heater. The natural gas has a
rating of 1000 Btu/ft
3
and a specific gravity
of 0.6 (Obtain these values from the local
gas supplier.)
 
BTU
ft
MBH
1000
1080
3
1080 ft
3
/hr
From the natural gas maximum capacities
table, at 100 ft and 1080 ft
3
/hr the required
minimum pipe size is 2”.
A 100 ft pipe run is needed for a 270 MBH
propane gas heater.
270 MBH = 270 kBtu/hr
From the propane gas maximum capacities
table, at 100 ft and 270 kBtu/hr the required
minimum pipe size is 1”.
Inlet and Manifold Pressures
For natural gas units, the minimum inlet gas
pressure to the unit is 6” w.c. and maximum
inlet gas pressure to the unit is 10.5” w.c.
For propane units, the minimum inlet gas
pressure to the unit is 11” w.c. and the
maximum inlet gas pressure to the unit is
13” w.c. A field provided 1/8” NPT pressure
tap is required to be installed in the piping
just upstream of the shutoff valve for test
gage connection to allow checking of the
gas supply pressure at the unit.
A factory installed pressure tap on the outlet
end of the gas valve can be used to verify a
manifold pressure of 3.5” w.c. for natural
gas, or 10.5” w.c. for propane.
Gas Pressure Regulator & Overpressure
Protection Device
A gas pressure regulator must be installed if
natural gas supply pressure to the unit is
greater than 10.5” w.c. and less than 2 psi
(55.4” w.c.) and if propane gas supply
pressure is greater than 13” w.c. and less
than 2 psi (55.4” w.c.). Regulators must
comply with the latest edition of the
Standard for Line Pressure Regulators,
ANSI Z21.80/CSA 6.22.
Both
a gas pressure regulator and
overpressure protection device (OPD) must
be installed if gas supply pressure to the unit
is greater than 2 psi (55.4” w.c.) and less
than 5 psi (138.4” w.c.), in compliance with
ANSI Z21.80/CSA 6.22. For proper heater
operation, pressure to the regulator MUST
NOT be greater than 5 psi (138.4” w.c.).
Piping Supports
Gas supply piping must be supported
directly at the connection to the unit and at
intervals listed in the following table with
metal straps, blocks, or hooks. Piping should
not be strained or bent.
Heater should be disconnected from
the gas supply piping during pressure
testing of the supply piping system
with pressures in excess of ½ psi. Gas
valves can be damaged if subjected to
more than ½ psi.
CAUTION