49
TABLE 11
SUPPLEMENTAL ORIFICE SIZE CHART
90 Plus ONLY models with 15,000 Btu's per Burner. DO NOT USE THIS CHART FOR ANY 80 PLUS MODEL.
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.
90 Plus Heat
Value at
15,000 Btu’s
per Burner
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)
46 18.57 808 46 46 47 47 47 48 48 49 49 50
47 17.52 856 47 47 48 48 49 49 49 50 50 51
48 16.36 917 48 48 49 49 49 50 50 50 51 51
49 15.2 987 49 49 50 50 50 51 51 51 52 52
50 13.92 1078 50 50 51 51 51 51 52 52 52 53
51 12.77 1175 51 51 51 52 52 52 52 53 53 53
15,000 14,400 13,800 13,200 12,600 12,000 11,400 10,800 10,200 9,600
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 (15,000 for 90 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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