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V. Gas Piping
TABLE 5: GAS RATINGS
TABLE 6: SPECIFIC GRAVITY CORRECTION
FACTORS FOR NATURAL GAS
WARNING
Failure to properly pipe gas supply to boiler may
result in improper operation and damage to the
boiler or structure. Always assure gas piping is
absolutely leak free and of the proper size and
type for the connected load.
An additional gas pressure regulator may be
needed. Consult gas supplier.
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. Refer to the boiler’s input
as printed on it’s rating label. Also consider existing
and expected future gas utilization equipment (i.e.
water heater, cooking equipment).
3. Length of piping and number of ttings. Refer to
Table 7 for maximum capacity of Schedule 40 pipe.
Table 8 lists equivalent pipe length for standard
ttings.
4. Corrections for the specic gravity of natural gas
can be found in Table 6.
For materials or conditions other than those listed
above, refer to National Fuel Gas Code, NFPA54/ANSI
Z223.1, or size system using standard engineering
methods acceptable to authority having jurisdiction.
NOTICE
SCG boilers built for altitudes greater than 4,999 feet above sea level need to be specially oriced to adjust for
changes in atmospheric conditions. The SCG boiler “H” Model has been certied to operate in atmospheric
conditions from 5,000 to 10,000 feet above sea level. Input is de-rated by 10% for applications at 5,000 feet
above sea level, and 20% for applications at 10,000 feet above sea levels. De-rate is based on 2% reduction
per 1000 feet.
The SCG boiler is available in two (2) altitude Models: The “S” Model 0 to 4,999 feet above sea level, and the
“H” Model 5,000 to 10,000 feet above sea level.
For applications above 10,000 feet, consult the manufacturer.
Boiler
Model
Number
Natural/LP
Maximum
Gas Pressure
(in. w.c.)
Minimum Natural
Gas Pressure
(in. w.c.)
Inlet to Gas Valve
Minimum LP
Gas Pressure
(in. w.c.)
Inlet to Gas Valve
Natural
Manifold
Pressure
(in. w.c.)
LP
Manifold
Pressure
(in. w.c.)
SCG-3
14 4.5 11.5 3.5 10.5
SCG-4
SCG-5
SCG-6
SCG-7
SCG-8
SCG-9
Specic
Gravity
Correction
Factor
Specic
Gravity
Correction
Factor
--- --- 0.85 0.81
--- --- 0.90 0.82
0.60 1.00 1.00 0.78
0.65 0.96 1.10 0.74
0.70 0.93 1.20 0.71
0.75 0.90 1.30 0.68
0.80 0.87 1.40 0.66