46
TABLE 6
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, determi
ne 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. Orifice
s 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 bu
rner is the intersection of
these two points on the chart above.
