37
90+ HIGH ALTITUDE
INSTRUCTIONS
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
SIZING THE BURNER ORIFICE, 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 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.
The necessary high altitude kits to use
with -GRL furnace models are listed
below:
NOTE: 278 Option Code is available
on -GRL models.
Alternately, 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 (example; a
90k BTU upflow furnace which is
factory converted for high altitude
elevations would have the model
number -GRL-09EZAJS
278
). These
factory converted furnaces come with a
pressure switch 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 -GRL
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.
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
/hr
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
!
CAUTION
!
CAUTION
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
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
5999 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
Annual Avg. Heat
Value (btu per ft
3
)
850
900
1000
1075
1170
TABLE 6
High Altitude Kit
-GRL Furnace Inputs
45,000, 60,000
RXGY-F18
(17” cabinets)
RXGY-F20
90,000 (21”)
HIGH ALTITUDE KIT
Installer must make necessary burner
orifice and pressure switch changes as
indicated in the table below:
-GRL PRESSURE SWITCH CHANGES
INPUT
HIGH ALTITUDE
SET POINT
SET POINT
KIT NO.
HIGH FIRE
LOW FIRE
45,000
RXGY-F18
-1.08
NO CHANGE
60,000
RXGY-F18
-1.08
NO CHANGE
90,000
RXGY-F20
-1.15
NO CHANGE
NOTE:
Orifices are no longer supplied
with kit.
