19
When a furnace is installed so that supply ducts carry air
circulated by the furnace to areas outside the space containing
the furnace, the return air shall also be handled by a duct
sealed to the furnace casing and terminating outside the space
containing the furnace.
E
DGES
OF
SHEET
METAL
HOLES
MAY
BE
SHARP
. U
SE
GLOVES
AS
A
PRECAUTION
WHEN
REMOVING
SHEET
METAL
FROM
RETURN
AIR
OPENINGS
.
WARNING
Filters - Read This Section Before Installing The
Return Air Ductwork
Filters must be used with this furnace. Discuss filter
maintenance with the building owner. Filters do not ship with
this furnace, but must be provided by the installer. Filters must
comply with UL900 or CAN/ULCS111 standards. Damage or
repairs due to failure to install filters in the furnace are not
covered under the warranty.
NOTE:
An undersized opening will cause reduced airflow.
Refer to the Filter Sizing Chart to determine filter area
requirements.
Upright Installations
Depending on the installation and/or customer preference,
differing filter arrangements can be applied. Filters can be
installed in the central return register or a side panel external
filter rack kit (upflows). As an alternative, a media air filter or
electronic air cleaner can be used as the primary filter. The
following figure shows possible filter locations.
FI
LTE
R
AIR FLOW
CENTRAL
RETURN
GRILLE
FI
LTE
R
SIDE RETURN
EXTERNAL FILTER
RACK KIT
(EITHER SIDE)
Upright Upflow
Figure 12
Circulation Air Filters
One of the most common causes of a problem in a forced
air heating system is a blocked or dirty filter. Circulating air
filters must be inspected monthly for dirt accumulation and
replaced if necessary. Failure to maintain clean filters can
cause premature heat exchanger failure.
A new home may require more frequent replacement until all
construction dust and dirt is removed. Circulating air filters are
to be installed in the return air duct external to the furnace
cabinet.
Upflow / Horizontal
Models
Minimum Recommended Filter Size^
*MES800403AU
1 - 16 X 25 Side or 1 -14 X 24 Bottom Return
*MES800603AU
1 - 16 X 25 Side or 1 -14 X 24 Bottom Return
*MES800604BU
1 - 16 X 25 Side or Bottom Return
*MES800804BU
1 - 16 X 25 Side or Bottom Return
*MES800805CU
2 - 16 X 25 Side Return, 1 - 20 X 25 Bottom Return
^Larger filters may be used, filters may also be centrally located
Table 7
