5808011-JIM-A-0320
Johnson Controls Ducted Systems
37
Figure 23: Bottom entry gas piping
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. Line should
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 22 and 23 for the
gas piping inlet location. Typical supply piping arrangements are
shown in Figures 22 and 23. 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.
OPTIONAL
COIL
GUARD
SHOWN
Table 14: Gas pipe sizing - capacity of pipe
Length of
pipe (ft.)
Nominal iron pipe size
3/4 in.
1 in.
1-1/4 in.
10
278
520
1050
20
190
350
730
30
152
285
590
40
130
245
500
50
115
215
440
60
105
195
400
70
96
180
370
80
90
170
350
90
84
160
320
100
79
150
305
Table 15: Gas heat minimum supply air
Size (tons)
Model
Heat size
Supply air (CFM)
Heating
Minimum
Maximum
J06
(6.5)
ZB
N12
1950
3250
N18
1950
3250
J07
(7.5)
ZB
N12
2250
3750
N18
2250
3750
J08
(8.5)
ZB
N12
2550
4250
N18
2550
4250
J10
(10)
ZB
N18
3000
5000
N24
3000
5000
J12
(12.5)
ZB
N18
3750
6250
N24
3750
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.