Lennox International Inc G50UH-60D-135, G50UH-48C-110, G50UH-36C-110, G50UH-36B-090, G50UH-60C-110

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TABLE 1

Furnace		Filter Size
Cabinet Size	Side Return		Bottom Return
14-1/2"	16X25X	1 (1)	14X25X1	(1)
17-112"	16X25X	1 (1)	16X25X1	(1)
21"	16X25X	1 (1)	20X25X	1 (1)
24-1/2"	16 X 25 X	1 (2)	24X25X	1 (1)

Use industry-approved standards to size and install the supply and return air duct system. This will result in a quiet and low-static system that has uniform air distribution.

NOTE - Do not operate the furnace with an external static pressure that exceeds 0,5 inches w,c, Higher external stat- ic pressures may cause erratic limit operation,

Supply Air Plenum

If the furnace is installed without a cooling coil, a removable access panel must be installed in the supply air duct, The access panel should be large enough to permit inspection (either by smoke or reflected light) of the heat exchanger for leaks after the furnace is installed, The furnace access panel must always be in place when the furnace is operat- ing and it must not allow leaks into the supply air duct sys- tem,

Return Air Plenum

Return air must not be drawn from a room where this furnace, or any other gas appliance (ie., a water heat- er), is installed. When return air is drawn from a room, a negative pressure is created in the room, If a gas ap- pliance is operating in a room with negative pressure, the flue products can be pulled back down the vent pipe and into the room, This reverse flow of the flue gas may result in incomplete combustion and the formation of carbon monoxide gas. This toxic gas might then be distributed throughout the house by the furnace duct system,

In upflow applications, the return air can be brought in through the bottom or either side of the furnace. If a fur- nace with bottom return air is installed on a platform, make an airtight seal between the bottom of the furnace and the platform to ensure that the unit operates properly and safely, Use fiberglass sealing strips, caulking, or equiva- lent sealing method between the plenum and the furnace cabinet to ensure a tight seal, Ifa filter is installed, size the return air duct to fit the filter frame.

A 4-inch diameter flue transition is factory-installed on the combustion air inducer outlet of all models. Modifying or removing the flue transition will cause the unit to oper- ate unsafely and will void the unit certification. The vent connector does not require insulation.

The combustion air inducer may be rotated clockwise or counterclockwise by 90° to allow for top or side vent dis- charge in all applications. When the unit is installed, the flue transition must be in the 9 o'clock, 12 o'clock or 3 o'clock position. The unit will not vent properly with the flue transition pointed down in the 6 o'clock position. Re- move the four mounting screws, rotate the assembly (in- cluding the gasket), then reinstall the mounting screws. See figure 14. Use the provided wire tie to bundle the pres- sure switch wires with the inducer motor power leads. Route the wires away from moving parts and the heat of the inducer motor to prevent damage to the wires.

Combustion Air Inducer

Flue Transition

(Do not remove)

Mounting	Screws	Power Leads
(Remove)
	FIGURE 14
	Optional	Flue Outlet
(Horizontal		Installation)
		Top View of Furnace
Top Cap ----__ _
Flue Outlet	_<_J	Supply Air
Hole /
		Opening
(Reattach	II 111

Cutout Here)

Optional

Flue Outlet

FIGURE 15

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