9
V. Gas Piping
A. Size gas piping. Design system to provide adequate gas
supply to boiler. Consider these factors:
1. Allowable pressure drop from point of delivery to
boiler. Maximum allowable system pressure is ½
psig. Actual point of delivery pressure may be less;
contact gas supplier for additional information.
Minimum gas valve inlet pressure is stamped on the
rating label located in the boiler's vestibule
compartment.
2. Maximum gas demand. Table 2 lists boiler input
rate. Also consider existing and expected future gas
utilization equipment (i.e. cooking equipment).
3. Length of piping and number of fi ttings. Refer to
Table 3 for maximum capacity of Schedule 40 pipe.
Table 4 lists equivalent pipe length for standard
fi ttings.
4. Specifi c gravity of gas. Gas piping systems for gas
with a specifi c gravity of 0.70 or less can be sized
directly from Table 3, unless authority having
jurisdiction specifi es a gravity factor be applied. For
specifi c gravity greater than 0.70, apply gravity
factor from Table 5. If exact specifi c gravity is not
shown choose next higher value.
For materials or conditions other than those listed
above, refer to National Fuel Gas Code, NFPA 54/
ANSI Z223.1, or size system using standard
engineering methods acceptable to authority having
jurisdiction.
B. Connect boiler gas valve to gas supply system.
1. Use methods and materials in accordance with local
plumbing codes and requirements of gas supplier. In
absence of such requirements, follow National Fuel
Gas Code, ANSI Z223.1.
2. Use thread (joint) compounds (pipe dope) resistant
to action of liquefi ed petroleum gas.
3. Install sediment trap, ground-joint union and manual
shut-off valve upstream of boiler gas control valve
and outside of jacket. See Figure 8.
4. All above ground gas piping upstream from manual
shut-off valve must be electrically continuous and
bonded to a grounding electrode. Do not use gas
piping as grounding electrode. Refer to National
Electrical Code, ANSI/NFPA 70.
Table 2: Rated Input
Table 3: Maximum Capacity of Schedule 40 Pipe in CFH For Gas Pressures of 0.5 psig or Less
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