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MANIFOLDPRESSUREAND ORIFICESIZE FORHIGH ALTITUDEAPPLICATIONS
NATURAL GAS
ElevationAbove Sea Level
Heat Value
BtulOu.Ft. 0-1999 2000-2999 3000-3999 4000-4999 5000-5999 6000-6999 7000-7999
(" .wc) (" .wc) (" .wc) (".wc) (" .wc) (".wc) (".wc)
800 3.5 3.5 3.5 3.5 3.5 3.5 3.5
850 3.5 3.5 3.5 3.5 3.5 3.5 3.5
900 3.5 3.5 3.5 3.5 3.5 3.5 3.4
950 3.5 3.5 3.5 3.5 3.3 3.2 3.1
1000 3.5 3.4 3.3 3.2 3.0 2.9 2.8
1050 3.2 3.1 3.0 2.9 2.7 2.6 2.5
1100 2.9 2.8 2.7 2.6 2.5 2.4 2.3
Orifice Size * #42 Orifice size for 50,000, 75,000 100,00 & 125,000 BTUH models
• #44 Orifice size for 80,000 BTUH model
General Derating Rules
For operation with natural gas at altitudes above 2,000',
orifice change andlor 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) or 4% (LP) for each 1,000'
above sea level. See Table 7 and Figure 28 for required
pressure change andlor orifice change for high altitudes.
For operation with LP gas at altitudes above 2,000', gas ori-
fices MUST be changed and manifold pressure MUST be
maintained as per Table 6. For the 50,000, 75,000,
100,000 and 125,000 BTUH Orifice sizes are #54 for
0-2000' above sea level, #55 for 2000' -7000' above sea
level, and #56 for 7000' -8000' above sea level. For the
80,000 BTUH models, the orifice size is #55 for 0 - 4,000'
above seal level and #56 for 5,000' - 8,000' above sea lev-
el. Orifices can be ordered through your distributor. (See
Figure 28)
Changing Orifices
Measure from face of orifice
NOTE: The derating of these units at 2% (Natural) and 4% (L.P.)
has been tested and approved by AGA.
High Altitude Air Pressure Switch
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.
Changing Orifices for High Altitude
ELECTRICAL SHOCK, FIRE OR EXPLOSION HAZARD
Failure to properly install orifices can result in death,
personal injury and/or property damage.
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.
NOTE: Main burner orifices can be changed for high altitudes.
1. Disconnect gas line from gas valve.
2. Remove manifold from furnace.
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 28)
5. Reinstall manifold. Ensure burners do NOT bind on new
orifices.
44001 111400 [_