2. ForoperationwithLPgasataltitudesabove2,000',gasori-
ricesMUST be changed and manifold pressure MUST be
maintained as per Table 6. Orifice sizes for 0-2000' above
sea level are #54. 2000-7000' above sea level, use #55.
7000-8000' above sea level, use #56 orifices. Orifices can
be ordered through your distributor. (See Figure 26)
NOTE: The derating of these units at 2% (Natural) and 4% (L R)
has been tested and approved by AGA.
HighAltitudeAir PressureSwitch
Altitudes over 4,000' require a different air pressure switch than
the one installed at the factory. Check parts list for pressure switch
and consult your distributor for part number and availability. In
Canada, provincial codes may govern installation of switch.
Check with governing authorities.
ChangingOrificesfor HighAltitude
Electrical shock, fire or explosion hazard.
Turn OFF electric power (at disconnect) and gas
supply (at manual valve in gas line) when
installing orifices. Installation of orifices requires
a qualified service technician.
Failure to properly install orifices can result in
death, personal injury and/or property damage.
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Typical Gas Piping for Upflow
NOTE: Main burner orifices can be changed for high altitudes.
1. Disconnect gas line from gas valve.
2. Remove combustion box front cover and manifold from fur-
nace.
3. Remove the orifices from the manifold and replace them
with properly sized orifices.
4. Tighten orifices so it is seated and gas tight. (See
Figure 26)
Changing Orifices
Measure from face of orifice
5. Reinstall manifold. Ensure burners do NOT bind on new
orifices.
Drip Leg and Union, Union* should
cabinet. Manual shut-off valve MUST be
of dripleg, union, and furnace.
Gas Pipe Grommet
(Single
Use elbows and 3" pipe
piping when using right
side gas pipe entry.
3" pipe
LP Low pressure
switch. Optional
on some models.
25-23-84
25-23-37
* Union may be installed inside the cabinet when necessary because of clearances.
NaturalGas Input RatingCheck
NOTE: The gas meter can be used to measure input to furnace.
Rating is based on a natural gas BTU content of 1,000 BTU's per
cubic meter. Check with gas supplier for actual BTU content.
1. Make sure combustion air box cover is in place and closed
before performing the following steps.
2. Turn OFF gas supply to all appliances and start furnace.
[_ 440 01 101004
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