Sears N9MP1, N9MP2, 9MPD manual Changing Orifices for High Altitude, General Derating Rules

MANIFOLDPRESSUREAND ORIFICE SIZE FOR HIGH ALTITUDEAPPLICATIONS

				NATURAL	GAS
Heat Value				ElevationAbove	Sea Level
	0-1999	2000-2999				6000-6999
BtulOu.Ft.			3000-3999	4000-4999	5000-5999		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.

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