Installation Guide
25
I&O manual
8.2 High Altitude Derate
Alternately standard derate for altitude from National Fuel Gas
Code ANSI Z223.1 of 4% per 1000' may be taken. Refer to the
most recent version of ASNI Z223.1 for correct gas orifice. The
orifices must be selected using the table below. The furnace
derate is 4% for each 1,000 feet above sea level. This table is
based upon a heating value of approximately 1,000 Btu/ft3.
When an appliance is installed at elevations above 4500ft (1350m),
the certified high-altitude input rating shall be reduces at the rate of
4% for each additional 1000ft (300m).
In some areas the gas supplier may artificially derate the gas in an
effort to compensate for the effects of altitude. If the gas is artificially
derated, the appropriate orifice size must be determined based upon
the BTU/ft3 content of the derated gas and the altitude. Refer to the
latest version of NFPA54/ANSI Z223.1 for US and the latest version
of CSA B149.1 for Canada., and information provided by the gas
supplier to determine the proper orifice size.
In Canada，,the input rating must be derated by 10 percent for
altitudes of 2,000 ft. (610m) to 4,500 feet (1370m) above sea level
by an authorized Gas Conversion Station or Dealer.
The input to the furnace must be checked AFTER reorificing.
*LP orifice based on 10 inWC manifold pressure
The input to the furnace must be checked AFTER reorificing.
For Canada application, based on regulation that requires 10% derating between 2000-4500ft. orifice change is NOT required up to 4500ft.
*LP orifice based on 10 inWC manifold pressure
Table 12 High Altitude Derate Orifice Size Chart (Natural and LP Gas*)
Canada Installation
US Installation
Input Rate Number of
KBTU/H Burner
Nat LP Nat LP Nat LP Nat LP Nat LP
60
3
4
5
5
6
47
5
7
48
58
49
59
50
60
100
5
45
5
6
47
57
48
58
49
59
50
60
80
4
4
5
5
6
47
57
48
58
49
59
50
60
12
0
6
45
5
6
47
57
48
58
49
59
50
60
Elevation (Ft)
0-2000
Elevation (Ft)
8000-10000
Elevation (Ft)
2000-4000
Elevation (Ft)
4000-6000
Elevation (Ft)
6000-8000
Input Rate Number of
KBTU/H Burner
Nat LP Nat LP Nat LP Nat LP Nat LP
60
3
4
5
5
6
45
5
6
48
58
49
59
50
60
100
5
45
5
6
45
56
48
58
49
59
50
60
80
4
4
5
5
6
45
56
48
58
49
59
50
60
120
6
45
5
6
45
5
6
48
58
49
59
50
60
Elevation (Ft)
0-2000
Elevation (Ft)
8000-10000
Elevation (Ft)
2000-4500
Elevation (Ft)
4500-6000
Elevation (Ft)
6000-8000