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Horizontal Application
Unit Installed on Platform
clearances.
GAS
ENTRY
VENT
PIPE
See the unit nameplate for
Line contact is permissible
SERVICE PLATFORM
FIGURE 13 
 WARNING
Improper installation of the furnace can result in personal 
injury  or  death.  Combustion  and  ue  products  must 
never be allowed to enter the return air system or the 
living space. Use screws and joint tape to seal the return 
air system to the furnace.
In platform installations with bottom return air, the furnace 
should be sealed airtight to the return air plenum. A 
door must never be used as a portion of the return air 
duct system. The base must provide a stable support 
and an airtight seal to the furnace. Allow absolutely no 
sagging, cracks, gaps, etc. The return and supply air 
duct systems must never be connected to or from other 
heating devices such as a replace or stove, etc. Fire, 
explosion, carbon monoxide poisoning, personal injury 
and/or property damage could result.
 WARNING
The blower access panel must be securely in place when 
the blower and burners are operating. Gas fumes, which 
could contain carbon monoxide, can be drawn into living 
space resulting in personal injury or death.
Filters
This unit is not equipped with a lter or rack. A eld-pro-
vided high-velocity lter is required for the unit to operate 
properly. Table 1 lists recommended lter sizes.
A lter must be in place any time the unit is operating.
 IMPORTANT
If a highefciency lter is being installed as part of this 
system to ensure better indoor air quality, the lter must 
be  properly  sized.  Highefciency  lters  have  a  higher 
static pressure drop than standardefciency glass/foam 
lters. If the pressure drop is too great, system capacity 
and performance may be reduced. The pressure drop 
may also cause the limit to trip more frequently during 
the winter and the indoor coil to freeze in the summer, 
resulting in an increase in the number of service calls.
Before  using  any  lter  with  this  system,  check  the 
specications provided by the lter manufacturer against 
the data given in the appropriate Lennox Product 
Specications bulletin. Additional information is provided 
in Service and Application Note ACC002 (August 2000).
TABLE 1 
Furnace Cabinet 
Width
Filter Size
Side Return Bottom Return
14-1/2” 16 X 25 X 1 (1) 14 X 25 X 1 (1)
17-1/2” 16 X 25 X 1 (1) 16 X 25 X 1 (1)
21” 16 X 25 X 1 (1) 20 X 25 X 1 (1)
24-1/2” 16 X 25 X 1 (2) 24 X 25 X 1 (1)