26
High Altitude Derate
When this furnace is installed at high altitude, the
appropriate High Altitude orifice kit must be applied. This is
required due to the natural reduction in the density of both
the gas fuel and combustion air as altitude increases. The
kit will provide the proper design certified input rate within
the specified altitude range.
High altitude kits are purchased according to the
installation altitude and usage of either natural or
propane gas. Consult the furnace Specification Sheet for
appropriate kits.
Do
not
derate the furnace by adjusting the manifold
pressure to a lower pressure than specified on the furnace
rating plate. The combination of the lower air density and a
lower manifold pressure will prohibit the burner orifice from
drawing the proper amount of air into the burner. This may
cause incomplete combustion, flashback, and possible
yellow tipping.
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/ft
3
content of
the derated gas and the altitude. Refer to the National
Fuel Gas Code, NFPA 54/ANSI Z223.1, and information
provided by the gas supplier to determine the proper orifice
size.
A different pressure switch may be required at high altitude
regardless of the BTU/ft
3
content of the fuel used. Consult
the furnace Specification Sheet for pressure switch.
WARNING
Possible property damage, personal injury or death may
occur if the correct conversion kits are not installed. The
appropriate kits must be applied to ensure safe and proper
furnace operation. All conversions must be performed by a
qualified installer or service agency.
Propane Gas Conversion
This unit is configured for natural gas, but may be
converted for use with L.P. gas. Refer to the section on
PROPANE GAS HIGH ALTITUDE INSTALLATIONS for L.P.
kit selection.
Consult the furnace Specification Sheet for a listing of
appropriate kits. The indicated kits must be used to insure
safe and proper furnace operation. All conversions must be
performed by a qualified installer, or service agency.
CAUTION
To prevent unreliable operation or equipment damage, the
inlet gas supply pressure must be as specified on the unit
rating plate with all other household has fired appliances
operating.
NOTE: If converting to LP gas, it is recommended
that an LPLP0* kit also be installed. The use of
this kit will prevent the furnace from firing when
the LP gas supply pressure is too low to support
proper combustion.
Gas Valve
This unit is equipped with a 24 volt gas valve controlled
during furnace operation by the integrated control
module. As shipped, the valve is configured for natural
gas. The valve is field convertible for use with propane
gas by replacing the regulator spring with a propane gas
spring from an appropriate manufacturer’s propane gas
conversion kit. Taps for measuring the gas supply pressure
and manifold pressure are provided on the valve.
The gas valve has a manual ON/OFF control located on
the valve itself. This control may be set only to the “ON”
or “OFF” position. Refer to the lighting instructions label
or
Startup Procedure & Adjustment
for use of this control
during start up and shut down periods.
Gas Piping Connections
The gas piping supplying the furnace must be properly
sized based on the gas flow required, specific gravity of the
gas, and length of the run. The gas line installation must
comply with local codes, or in their absence, with the latest
edition of the National Fuel Gas Code, NFPA 54/ANSI
Z223.1.
Natural Gas Capacity of Pipe
In Cubic Feet of Gas Per Hour (CFH)
Length of
Nominal Black Pipe Size
Pipe in Feet
1/2"
3/4"
1"
1 1/4"
1 1/2"
10
132
278
520
1050
1600
20
92
190
350
730
1100
30
73
152
285
590
980
40
63
130
245
500
760
50
56
115
215
440
670
60
50
105
195
400
610
70
46
96
180
370
560
80
43
90
170
350
530
90
40
84
160
320
490
100
38
79
150
305
460
(Pressure 0.5 psig or less and pressure drop of 0.3" W.C.; Based on
0.60 Specific Gravity Gas)
CFH = BTUH Furnace Input
Heating Value of Gas (BTU/Cubic Foot)
To connect the furnace to the building’s gas piping, the
installer must supply a ground joint union, drip leg, manual
shutoff valve, and line and fittings to connect to gas valve.
In some cases, the installer may also need to supply a
transition piece from 1/2” pipe to a larger pipe size.
The following stipulations apply when connecting gas
piping. Refer to
Gas Piping Connections
figure for typical
gas line connections to the furnace.
•
Gas piping must be supported external to the furnace
cabinet so that the weight of the gas line does not
distort the burner rack, manifold or gas valve.
