Venting - Lennox SL280UH090V36B Installation Instructions Manual

reverse flow of the flue gas may result in incomplete com-
bustion 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. If a filter is installed, size the
return air duct to fit the filter frame.

Venting

A 4-inch diameter flue transition is factory-installed on
the combustion air inducer outlet of all models. Figure 16
shows the combustion air inducer as shipped from
the factory.
Mounting Screws Location
mounting screw
FIGURE 15
IMPORTANT
The unit will not vent properly with the flue transition
pointed down in the 6 o'clock position. The combustion
air inducer may be rotated clockwise or counterclockwise
by 90° to allow for top or side vent discharge 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.
If necessary reposition the combustion air inducer, pres-
sure switch and or make up box as needed per the follow-
ing steps and see figures 16 through 22.
1 - Remove the four mounting screws (figure 15)
whic secure the combustion air inducer / pressure
switch assembly to the orifice plate. Lift and rotate
the assembly 90 degrees clockwise or counter
clockwise to either the 3 o'clock position or to 9
o'clock position and re-secure with four screws.
Gasket should be left in place.
mounting screws
Page 13
2 - Use tin snips to cut preferred opening on the
cabine for repositioning the flue outlet. Use the cut
out piece as a cover plate to patch unused opening
on cabinet.
UPFlow Position
UPFLOW POSITION
Top Vent Discharge
flue
transition
pressure
switch
make-up
box
FIGURE 16
UPFLOW POSITION
Left Side Vent Discharge
cover plate
pressure
switch
vent pipe
flue
transition
Gas supply piping must be brought into the unit from the right
side in order to accommodate the flue pipe.
Remove make-up box assembly (2 screws) and cut wire tie to
free make-up box wires. Re-install make-up box on other side
of cabinet.
Re-secure make-up box wires, either pulling excess wires
through the blower compartment and securing with supplied
wire tie, or coil excess wire and secure to the gas manifold.
FIGURE 17
vent pipe
collector box
FLOW
AIR
collector box
make-up
FLOW
AIR
box