5566019-BIM-B-1118
34 Johnson Controls Ducted Systems
Optional gas heat
The optional gas-fired heaters have aluminized-steel or optional
stainless steel, tubular heat exchangers with spark ignition.
Note: On VAV units: individual VAV boxes must be fully open
in heating mode to ensure airflow falls within the
specified temperature rise range.
Gas piping
Proper sizing of gas piping depends on the cubic feet per hour
of gas flow required, specific gravity of the gas, and the length
of run.
Follow the “National Fuel Gas Code” Z223.1 (in U.S.A.) or the
current Gas Installation Codes CSA-B149.1 (in Canada) in all
cases unless they are superseded by local codes or gas utility
requirements.
See Table 16, Gas pipe sizing - capacity of pipe, on page 34.
The heating value of the gas may vary by locality. You must
check the value with the local gas utility.
Figure 25: Side entry gas piping
Figure 26: 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. The line
must not be sized smaller than the entrance fitting size.
Table 16: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
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