MG & SG Series Boilers – Installation and Service Manual
16
3.6 CHECK INPUT & ORIFICES
For safety, the input shown on rating plate must not be exceeded. Check with the table below that
the orifice size and input rate shown on your boiler rating plate match your application, i.e. boiler model,
fuel type, and altitude. See MG & SG Specifications to find a boiler model's input rate.
FOR CANADA
Natural Gas Propane
Model
0 to 2,000 feet 2,000 to 4,500 feet 0 to 2,000 feet 2,000 to 4,500 feet
MG
#51 orifice
standard input
#51 orifice
standard input
#60 orifice
standard input
#61 orifice
10% derate input
SG
#43 orifice
standard input
#44 orifice
10% derate input
#54 orifice
standard input
#55 orifice
10% derate input
NOTE: For elevations above 4,500 feet reduce high altitude input 4% for each additional 1000 feet.
Reference Natural Gas and Propane Installation Code B149.1, 3.22 High Altitude Installations
Example of High Altitude Derate
Boiler: SG-270
Altitude: 5,500 feet
Standard Input (0 to 2,000 ft) = 270,000 Btu/h (from page 3)
High Altitude Input (2,000 to 4,500 ft) = Derate Standard Input by 10% (see above
table)
= 270,000 Btu/h x (1 - 0.10)
= 270,000 Btu/h x 0.90
= 243,000 Btu/h
% Reduction for additional 1000 ft = 4% x 1 = 4%
Input at 5,500 ft = Derate High Altitude Input by 4%
= 243,000 Btu/h x (1 – 0.04)
= 243,000 Btu/h x 0.96
= 233,280 Btu/h
FOR UNITED STATES
Natural Gas Propane
Model
0 to 2,000 feet Over 2,000 feet 0 to 2,000 feet Over 2,000 feet
MG
#51 orifice
standard input
#60 orifice
standard input
SG
#43 orifice
standard input
Input must be reduced
4% for each 1000 feet
above sea level. *
#54 orifice
standard input
Input must be reduced
4% for each 1000 feet
above sea level. *
*Reference National Fuel Gas Code ANSI Z223.1, 8.1.2 High Altitude.
Example of High Altitude Derate
Boiler: MG-100
Altitude: 5,000 feet
Standard Input (0 to 2,000 ft) = 100,000 Btu/h (from page 2)
% Reduction for 5,000 ft = 4% x 5 = 20%
Input at 5,000 ft = Derate Standard Input by 20%
= 100,000 Btu/h x (1 - 0.20)
= 100,000 Btu/h x 0.80
= 80,000 Btu/h
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