42
90+ HIGH ALTITUDE
INSTRUCTIONS
90RJ/90TJ HIGH ALTITUDE
KITS
All 90RJ/90TJ models can be
converted for high altitude usig the
appropriate High Altitude Conversion
Kits listed below. The kits can be
ordered from the factory. The kit
includes pressure switch(es) and
instructions for converting the furnace
for elevations above 5,000 ft. The kit
should never be used at elevations
below 5,000 ft. In addition, the kit
instructions detail how to re-calculate
burner orifice size based on gas
heating value and elevation. The
instructions are based on a required
4% per thousand feet reduction in
input as specified by the National
Fuel Gas Code (NFGC). Specific
orifices should always be recalculated
for all high altitude installations as
outlined below. Orifices should be
changed, if necessary, based on gas
heating value and elevation.
90RJ/90TJ
-HIGH ALTITUDE OPTION
#278
Furnaces can be ordered from the
factory already converted for high
altitude elevations. The factory option
for high altitude elevations would be
ordered as a 278 option. These
factory converted furnaces come with
pressure switches for high-altitude
elevations already attached. Also,
different burner orifices are installed
at the factory which are one drill size
smaller (#51 DMS) than standard
90RJ/90TJ gas furnaces (#50 DMS).
The smaller orifice is installed to
accommodate for average heating
values expected in most high altitude
areas and a required 4% per
thousand feet reduction in input as
specified by the National Fuel Gas
Code (NFGC). Specific orifices
should always be recalculated for all
high altitude installations as outlined
below. Orifices should be changed, if
necessary, based on gas heating
value and elevation.
NATURAL GAS
THE NATIONAL FUEL GAS CODE
(NFGC) GUIDELINES SHOULD BE
FOLLOWED WHEN CONVERTING
THESE FURNACES FOR HIGH
ALTITUDE OPERATION.
ELEVATIONS ABOVE 2000 FT
REQUIRE THAT THE FURNACE
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
DETERMINE IF AN ORIFICE CHANGE
WILL BE NECESSARY AND HOW TO
DETERMINE THE NEW ORIFICE
SIZE.
IN CANADA, AS AN ALTERNATE TO
ADJUSTING THE BURNER ORIFICE
SIZE, THE MANIFOLD GAS
PRESSURE MAY BE ADJUSTED.
THIS METHOD IS COVERED LATER
IN THIS SECTION. THIS METHOD OF
ADJUSTING MANIFOLD PRESSURE
MAY ONLY BE USED IN CANADIAN
INSTALLATIONS.
34 90 Plus furnaces installed at high
elevations require the installation of a
high altitude kit for proper operation. The
high altitude kit consists of a high
altitude pressure switch that replaces
the pressure switch attached to the
induced draft blower. The kit also
contains gas orifices for high altitude.
The pressure switch must be installed at
elevations above 5000 ft. 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
altitudes.
The following are examples of orifice
sizing using the National Fuel Gas
Code Appendix F. For a simplified
estimation of orifice size based on
heating value and elevation, use
Tables 5 and 6. 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
I = Sea Level input (per burner):
15000
H = Sea Level Heating Value: 900
Q = 16.68 ft
3
Natural Gas per hour.
From Table F.1 of National Fuel Gas
Code Handbook, 2002 (3.5 w.c.
column)
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
Example: 1050 BTU/ft
3
Regional
Natural Gas Heating Value
I / H = Q
15000 / 1050 = 14.63 ft.
3
I = Sea Level input (per burner):
15000
H = Sea Level Heating Value: 1050
Q = 14.28 ft.
3
Natural Gas per hour.
From Table F.1 of National Fuel Gas
Code Handbook, 2002 (3.5 w.c.
column)
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 thousand ft.): #51
Orifice required at 8000 ft. elevation
(4% de-rate per thousand ft.): #52
Natural Gas Orifice Drill Size (4% per 1000 ft. De-Rate)
IMPORTANT: 90 Plus Models only. Do not use this chart for any 80 Plus Models
Burner Input (per burner) 15,000 BTU @ Sea Level
Annual Avg. Heat
Value (btu per ft
3
)
850
900
1000
1075
1170
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
Sea level
to 1999 ft
2000 to
2999 ft
3000 to
3999 ft
4000 to
4999 ft
5000 to
5999 ft
6000 to
6999 ft
7000 to
7999 ft
8000 to
8999 ft
!
CAUTION
High
Altitude Kit 90RJ/90TJ
RXGY-F04 105,000 BTU’s
RXGY-F05 120,000
RXGY-F06 45,000, 60,000 & 90,000
RXGY-F07 75,000
TABLE 5
!
CAUTION
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