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Improper installation of the furnace can result in per
sonal injury or death. Combustion and flue 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 ple
num. 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. Al
low 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 fireplace or stove, etc. Fire, explosion, carbon
monoxide poisoning, personal injury and/or proper
ty damage could result.
WARNING
Filters
This unit is not equipped with a filter or rack. A field-pro
vided high-velocity filter is required for the unit to operate
properly. Table 2 lists recommended filter sizes.
A filter must be in place any time the unit is operating.
IMPORTANT
If a highefficiency filter is being installed as part of
this system to ensure better indoor air quality, the fil
ter must be properly sized. Highefficiency filters
have a higher static pressure drop than standardef
ficiency glass/foam filters. If the pressure drop is too
great, system capacity and performance may be re
duced. 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 filter with this system, check the
specifications provided by the filter manufacturer
against the data given in the appropriate Lennox
Product Specifications bulletin. Additional informa
tion is provided in Service and Application Note
ACC002 (August 2000).
Furnace
Cabinet
Side Return
Width
A - 338
406 X 635 X 25 1
(14-1/2")
(16 X 25 X 1)
B- 446
406 X 635 X 25 1
( 17-1/2")
(16 X 25 X 1)
C - 533
405 X 635 X 25 1
( 21")
(16 X 25 X 1)
D - 622
405 X 635 X 25 2
(24-1/2")
(16 X 25 X 1)
Duct System
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 in the heating mode
with an external static pressure that exceeds 125Pa (0.5"
w.c.) Higher external static 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.
Unit Capacity
NOTE - The number of outlets was calculated for the facto
ry set heating speed tap.
Return Air Plenum
NOTE - Return air must not be drawn from a roomwhere
this furnace, or any other gas-fueled appliance
(i.e., water heater), or carbon monoxide producing device
(i.e., wood fireplace) is installed.
When return air is drawn from a room, a negative pres
sure is created in the room. If a gas appliance 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 com
bustion and the formation of carbon monoxide gas. This
toxic gas might then be distributed throughout the house
by the furnace duct system.
Page 11
TABLE 2
Filter Size mm (in) and Quantity
Bottom Return
356 X 635 X 25 1
(14 X 25 X 1)
406 X 635 X 25 1
(16 X 25 X 1)
508 X 635 X 25 1
(20 X 25 X 1)
610 X 635 X 25 1
(24 X 25 X 1)
TABLE 3
Minimum Number of Outlets
5
7
8
9
10
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