36
High Altitude
HIGH ALTITUDE
34" 80 Plus furnaces installed above 2,000 ft. require the furnace
to be de-rated 4% per thousand feet.
IMPORTANT: Factory installed orifices are calculated and sized
based on a sea level Natural Gas heating value of 1050 BTU per
cubic ft.
NOTE: Orifices are available through your local distributor.
Reference Table 8 for approximate orifice sizing.
The following are examples of orifice sizing using the National
Fuel Gas Code Appendix F:
For a simplified estimation of orifice size based on gas heating
value and elevation, Table 8 may be used. However, calculations
are the best method.
Example: 900 BTU/ft
3
Regional Natural Gas Heating Value
I/H = Q
25000 / 900 = 27.78 ft
3
I = Sea Level input (per burner): 25000
H = Sea Level Heating Value: 900
Q = 27.78 ft
3
Natural Gas per hour.
From Table F.1 of National Fuel Gas Code Handbook, 2002 (3.5ⴖ
w.c. column).
Orifice required at Sea Level: #40
From Table F.4 of National Fuel Gas Code Handbook, Orifice re-
quired at 5000 ft. elevation (4% de-rate per thousand ft): #42
Orifice required at 8000 ft. elevation (4% de-rate per thousand ft.):
#44
Example: 1050 BTU/ft3 Regional Natural Gas Heating Value
I / H = Q
25000 / 1050 = 23.81ft
3
I = Sea Level input (per burner): 25000
H = Sea Level Heating Value: 1050
Q = 23.81 ft
3
Natural Gas per hour.
From Table F.1 of Natural Fuel Gas Code Handbook, 2002 (3.5⬙
w.c. column).
Orifice required at Sea Level: #43
From Table F.4 of National Fuel Gas Code Handbook, 2002
Orifice required at 5000 ft. elevation (4% de-rate per
thousand ft.): #45
Orifice required at 8000 ft elevation (4% de-rate per
thousand ft): #47
ORIFICE ORDERING INFORMATION
Orifice sizes are selected by adding the 2-digit drill size required in
the orifice part number. Drill sizes available are 39 through 64;
metric sizes available 1.10mm (-90) and 1.15mm (-91):
Orifice Part Number 62-22175-(drill size)
Example 1:
# 60 drill size orifice required
Part # 62-22175-60
Example 2:
1.15mm drill size orifice required
Part # 62-22175-91
NATURAL GAS AT HIGH ALTITUDES
!
WARNING
INSTALLATION OF THIS FURNACE AT ALTITUDES ABOVE
2000 FT (610 m) SHALL BE IN ACCORDANCE WITH
LOCAL CODES, OR IN THE ABSENCE OF LOCAL CODES,
T
HE NATIONAL FUEL GAS CODE, ANSI Z223.1/NFPA 54
OR NATIONAL STANDARD OF CANADA, NATURAL GAS
AND PROPANE INSTALLATION CODE, CAN B149.1.
!
C
AUTI
ON
ELEVATIONS ABOVE 2000 FT. REQUIRE THAT THE FUR-
NACE INPUT RATING BE ADJUSTED AND THAT THE SIZE
OF THE BURNER ORIFICES BE RE-CALCULATED BASED
ON ELEVATION AND GAS HEATING VALUE. THE BURNER
ORIFICES MAY (OR MAY NOT) NEED TO BE CHANGED.
THE FOLLOWING EXAMPLES SHOW HOW TO DETER-
MINE IF AN ORIFICE CHANGE WILL BE NECESSARY
AND HOW TO DETERMINE THE NEW ORIFICE SIZE.
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