Table of Contents
Advertisement
5.
Set pressure to value shown in Table 7. Refer to Impor-
tant Notes in Table 7. Pressure is also listed on furnace
rating plate.
6.
When pressure is set, replace adjustment screw cover on
gas valve.
7.
Replace combustion air box cover.
NOTE: Adjustment screw cover MUST be replaced on gas valve
BEFORE reading manifold pressure and operating furnace.
2,
For operation with LP gas at altitudes above 2,000', gas
orifices MUST be changed and manifold pressure MUST
be maintained as per Table 7. 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.
GeneralDeraUngRules
1.
For operation with natural gas at altitudes above 2,000',
orifice change and/or manifold pressure adjustment may
be required to suit gas supplied. Check with gas supplier. If
orifice sizing is needed, it should be based on reducing the
input rating by 2% (natural) 4% (LP) for each 1,000' above
sea level. See Table 8 and Figure 23 for required pres-
sure change and/or orifice change for high altitudes.
MANIFOLD PRESSURE
AND ORIFICE SIZE FOR HIGH ALTITUDE
APPLICATIONS
Heat Value
Btu/Cu.Ft.
8OO
850
900
95O
1000
1050
1100
Orifice Size
0-1999
("-wc)
3.5
3.5
3.5
3.5
3.5
3.2
2.9
#42
2000-2999
(" .wc)
3.5
3.5
3.5
3.5
3.4
3.1
2.8
#42
3000-3999
(" -wc)
3.5
0.5
3.5
0.5
3.3
3.0
2.7
#42
NATURAL GAS
ElevationAbove Sea Level
4000-4999
5000-5999
(" .we)
(" -wc)
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.3
3.2
3.0
2.9
2.7
2.6
2.5
#42
#42
6000-6999
(" -wc)
3.5
3.5
3.5
3.2
2.9
2.6
2.4
#42
7000-7999
(" "wc)
3.5
3.5
3,4
3.1
2.8
2.5
2.3
#42
High AltitudeAir 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 availabil-
ity. In Canada, provincial codes may govern installation of switch.
Check with governing authorities.
ChangingOrificesfor HighAltitude
1.
Disconnect gas line from gas valve.
2.
Remove combustion box front cover and manifold from
furnace,
3.
Remove the orifices from the manifold and replace them
with properly sized orifices.
4.
Tighten orifices so there is 11/16"(27mm) from the faces of
the orifices to the back side ofthe manifold, Figure 23..
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
property damage, personal injury and/or death.
NOTE: Main burner
orifices
can be changed
for high altitudes.
Changing Orifices
Measure 11/16" (27ram) from
face of orifice to the back side
of the manifold,
5.
Reinstatl manifold and combustion air box cover. Ensure
burners do NOT bind on new orifices.
NaturalGas Input RatingCheck
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 startfurnace.
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.
3.
Time how many seconds it takes the smallest dial on the
gas meter to make one complete revolution. Refer to Ex-
ample.
Advertisement
Table of Contents
