99
Table 34 - Natural Gas (ft
3
/hr) Maximum Piping Capacities
Specific Gravity = 0.6, Supply Pressure ≤ 0.5 psi, Pressure Drop = 0.5” w.c.
Table 35 - Propane (kBtu/hr) Maximum Piping Capacities
Specific Gravity = 1.52, Supply Pressure = 11” w.c., Pressure Drop, 0.5” w.c.
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.)
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.
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