66
RT-SVX24Q-EN
well as damage the gas valve. Oversizing the
regulator will cause irregular pulsating flame
patterns, burner rumble, potential flame outages,
and possible gas valve damage.
If a single pressure regulator serves more than one
rooftop unit, it must be sized to ensure that the inlet
gas pressure does not fall below 7" w.c. with all the
furnaces operating at full capacity. The gas
pressure must not exceed 14" w.c. when the
furnaces are off.
7. Provide adequate support for all field installed gas
piping to avoid stressing the gas train and controls.
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8. Leak test the gas supply line using a soap-and-
water solution or equivalent before connecting it to
the gas train.
9. Check the supply pressure before connecting it to
the unit to prevent possible gas valve damage and
the unsafe operating conditions that will result.
NNoottee:: Do not rely on the gas train shutoff valves to
isolate the unit while conducting gas
pressure/leak test. These valves are not
designed to withstand pressures in excess of
14" w.c. or 0.5 psig.
Connecting the Gas Supply Line to the
Furnace Gas Train
Follow the steps below to complete the installation
between the supply gas line and the furnace. Refer to
Figure 49, p. 67 and Figure 50, p. 67, for the
appropriate gas train configuration.
1. Connect the supply gas piping using a “ground-
joint” type union to the furnace gas train and check
for leaks.
2. Adjust the inlet supply pressure to the
recommended 7" to 14" w.c. parameter for natural
gas.
3. Ensure that the piping is adequately supported to
avoid gas train stress.
4. If the through the base gas opening is used, seal off
around the pipe and the 3" water dam. If the
through the base gas opening is not used, the 3"
opening should be sealed shut to prevent indoor air
leakage.
Table 23. Sizing natural gas pipe mains and branches
Gas SupplyPipe Run
(ft)
Gas Input (Cubic Feet/Hour)
1¼" Pipe 1½" Pipe 2" Pipe 2½" Pipe 3" Pipe 4" Pipe
10
1,060 1,580 3,050 4,860 8,580 17,500
20 726
1,090 2,090 3,340 5,900 12,000
30 583 873
1,680 2,680 4,740 9,660
40 499 747
1,440 2,290 4,050 8,270
50 442 662
1,280 2,030 3,590 7,330
60 400 600
1,160 1,840 3,260 6,640
70 368 552
1,060 1,690 3,000 6,110
80 343 514 989
1,580 2,790 5,680
90 322 482 928
1,480 2,610 5,330
100 304 455 877
1,400 2,470 5,040
125 269 403 777
1,240 2,190 4,460
150 244 366 704
1,120 1,980 4,050
175 224 336 648
1,030 1,820 3,720
IInnssttaallllaattiioonn
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