41
TABLE 11
Natural Gas Orifice Drill Size (4% per 1000 ft. De-Rate)
IMPORTANT: For 90+ Furnaces only. Do not use this chart for any 80+ Furnace.
Burner Input (per burner) 15,000 BTU @ Sea Level
Sea level 2000 to 3000 to 4000 to 5000 to 6000 to 7000 to 8000 to
to 1999 ft 2999 ft 3999 ft 4999 ft 5999 ft 6999 ft 7999 ft 8999 ft
47 48 48 49 49 49 50 50
48 49 49 49 50 50 50 51
49 50 50 50 51 51 51 52
50 51 51 51 51 52 52 52
51 51 52 52 52 53 53 53
RGFG- HIGH ALTITUDE
CONVERSION
FOR ALL MODELS, A PRESSURE
SWITCH CHANGE IS NOT NECES-
SARY AT ANY ELEVATION UP TO
8,000 FT. HOWEVER, AT ELEVATIONS
ABOVE 5,000 FT., AN ORIFICE
CHANGE MAY BE REQUIRED. FUR-
NACES A
RE N
OT TESTED ABOVE
8,000 FT. AND CANNOT BE
INSTALLED ABOVE 8,000 FT.
Orifice Selection for High Altitude
Applications For U.S. Installations
Natural Gas
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, THE NATIONAL
FUEL GAS CODE, ANSI Z223.1/NFPA
54 OR NATIONAL STANDARD OF
CANADA, NATURAL GAS AND
PROPANE INSTALLATION CODE,
C
AN
B149.1.
Elevations above 2000 ft. require the
furnace to be de-rated 4% per thousand
feet. NOTE: Factory installed orifices are
calculated and sized based on a sea
level Natural Gas heating value of 1075
BTU per cubic ft. Regional reduced
heating values may nullify the need to
change orifices except at extreme alti-
tudes. Table 11 shows some quick con-
versions based on elevation and gas
heating value. Th
is t
able is combined
and simplified from Tables F1 and F4 of
the National Fuel Gas Code.
EXAMPLES
The following are examples of orifice
sizing using the National Fuel Gas
Code Appendix F. For a simplified esti-
mation of orifice size based on heating
value and elevation use Tables 11 and
12. However, calculations are the best
method.
Example: 900 BTU/ft
3
Regional
Natural Gas Heating Value
I / H = Q
15000 / 900 = 16.68 ft
3
/hr
I = Sea Level input (per burner): 15000
H = Sea Level Heati
ng Va
lue: 900
Q = 16.68 ft
3
Natural Gas per hour.
From Table F.1 of National Fuel Gas
Code Handbook, 2002 (3.5ⴖ w.c. col-
umn)
Orifice required at Sea Level: # 48
From Table F.4 of National fuel Gas
Code Handbook, 2002
Orifice required at 5000 ft. elevation
(4% de-rate per thousand ft): # 50
Orifice required at 8000 ft. elevation
(4% de-rate per thousand ft): # 51
Annual Avg. Heat
Value (btu per ft
3
)
850
900
1000
1075
1170
Example: 1050 BTU/ft
3
Regional
Natural Gas Heating Value
I / H = Q
15000 / 1050 = 14.63 ft
3
/hr
I = Sea Level input (per burner):
15000
H = Sea Level Heating Value: 1050
Q= 14.28 ft
3
Natural Gas.
From Table F.1 of National Fuel Gas
code Handbook, 2002 (3.5ⴖ w.c. col-
umn)
Orifice required at Sea Level: # 50
From Table F.4 of National Fuel Gas
code Handbook, 2002
Orifice required at 5000 ft. elevation
(4% de-rate per t
housand ft): # 51
Orifice required at 8000 ft. elevation
(4% de-rate per thousand ft): # 52
CAUTION
!
!
WARNING
HIGH ALTITUDE INSTALLATIONS IN THE U.S.
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