5835254-YIM-A-1119
26
Johnson Controls Ducted Systems
NOTE:
Maximum capacity of pipe in cubic feet of gas per hour
based upon a pressure drop of 0.3 inch W.C. and 0.6
specific gravity gas.
NOTE:
There may be a local gas utility requirement specifying a
minimum diameter for gas piping. All units require a 3/4
inch pipe connection at the entrance fitting. The line
must not be sized smaller than the entrance fitting size.
Gas connection
Route the gas supply line within the space and roof curb with the
exit through the unit’s basepan. See Figures 8 and 8 for the gas
piping inlet location. Typical supply piping arrangements are
shown in Figures 23 and 24. All pipe nipples, fittings, and the gas
cock are field supplied or may be purchased in the Ducted
Systems accessory kit #1GP0405.
Apply the following gas piping recommendations.
• You must install a drip leg and a ground joint union in the
gas piping.
• When required by local codes, install a manual shut-off
valve outside of the unit.
• Use wrought iron or steel pipe for all gas lines. Apply pipe
dope sparingly to male threads only.
• Clean all piping of dirt and scale. Hammer on the outside
of the pipe and blow out loose particles. Before initial
start-up, make sure that all gas lines external to the unit
are purged of air.
• The gas supply must be a separate line and installed in
accordance with all safety codes as prescribed under
Limitations.
• You must install a 1/8-inch NPT plugged tapping,
accessible for test gage connection, immediately
upstream of the gas supply connection to the unit.
• After the gas connections are complete, open the main
shut-off valve admitting
normal gas pressure
to the mains.
Check all joints for leaks with soap solution or other
material suitable for the purpose.
Never use a flame.
LP units, tanks, and piping
All gas heat units are shipped from the factory equipped for
natural gas use only. The unit may be converted in the field for
use with LP gas with accessory kit model 1NP0442.
All LP gas equipment must conform to the safety standards of
the National Fire Protection Association.
Table 14: Gas heat minimum supply air
Size (tons)
Model
Heat size
Supply air (CFM)
Cooling
Heating
Minimum
Maximum
Minimum
Maximum
15
(15)
ZZ
N18
4500
6250
4500
6250
N24
4500
6250
4500
6250
Natural gas may contain some propane. Propane is an
excellent solvent and will quickly dissolve white lead and
most standard commercial compounds. A special pipe
dope must be used when assembling wrought iron or
steel pipe. Shellac based compounds such as Gaskolac
or Stalastic, and compounds such as Rectorseal #5,
Clydes’s or John Crane may be used.
Fire or explosion hazard
Failure to follow the safety warning exactly could result
in serious injury, death, or property damage.
Never test for gas leaks with an open flame. Use a
commercially available soap solution made specifically
for the detection of leaks to check all connections. A fire
or explosion may result causing property damage,
personal injury, or loss of life.
The furnace and its individual shut-off valve must be
disconnected from the gas supply piping system during
any pressure testing at pressures in excess of 1/2 PSIG.
Pressures greater than 1/2 PSIG will cause gas valve
damage resulting in a hazardous condition. If it is
subjected to a pressure greater than 1/2 PSIG, the gas
valve must be replaced.
The furnace must be isolated from the gas supply piping
system by closing its individual manual shut-off valve
during any pressure testing of the gas supply piping
system at test pressures equal to or less than 1/2 PSIG.
Threaded joints must be coated with a sealing
compound that is resistant to the action of liquefied
petroleum gases.
Do not use Teflon tape.
