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TABLE 8
SUPPLEMENTAL ORIFICE SIZE CHART
80 Plus Models with 25,000 Btu's per Burner
NATURAL GAS QUICK REFERENCE CHART FOR ORIFICE SELECTION, AT 3.5" W.C. AND APPROXIMATE FINAL FIRING RATES
Final Firing Rate per Burner
Sea Level
Orifice
Size
Sea Level
Cubic
Foot at
3.5" W.C.
80 Plus
Heat
Value at
25,000
0-999 1000-1999 2000-2999 3000-3999 4000-4999 5000-5999 6000-6999 7000-7999 8000-8999 9000-9999
ELEVATION CHART (NFG recommended orifice based on 4% derate for each 1000 foot of elevation, based on the intersection of the
orifice required at Sea Level and the elevation required below)
37 30.63 816 37 37 38 39 39 40 41 42 42 43
38 29.25 855 38 38 39 40 41 41 42 42 43 43
39 28.2 887 39 39 40 41 41 42 42 43 43 44
40 27.03 925 40 40 41 42 42 42 43 43 44 44
41 25.98 962 41 41 42 42 42 43 43 44 44 45
42 24.95 1002 42 42 42 43 43 43 44 44 45 46
43 22.39 1117 43 43 44 44 44 45 45 46 47 47
44 21.01 1190 44 44 45 45 45 46 47 47 48 48
25,000 24,000 23,000 22,000 21,000 20,000 19,000 18,000 17,000 16,000
All calculations are performed by using the first three columns of information only. Before beginning any calculations, determine the individual burner Btu size
and heating value at Sea Level for the installation site. Each value shown in the Heat Value column is per burner at 3.5" W.C.
NOTE:
Heat Value at Sea Level, for the location of the installation, is available from the Natural Gas Supplier to that site. Orifices for all altitudes are based on Sea Level values.
Divide the individual burner capacity (25,000 for 80 plus) by the Heat Value for the site to determine the Cubic Foot value at Sea Level, or divide burner capacity by the Cubic
Foot value for the Heat Value. Once you have either the Cubic Foot Value or the Heat Value you can estimate the Sea Level orifice for the site. To select the corresponding
high altitude orifice, locate the site elevation on the chart above and the orifice required at Sea Level from your calculation in the first column. The correct high
altitude orifice that must be installed in each individual burner is the intersection of these two points on the chart above.
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