PRODUCT DESIGN
71
As an alternative a media air filter or electronic air cleaner
can be used as the requested filter. Refer to the following
minimum filter requirement charts for determination of the
minimum filter area to ensure proper unit performance. The
following figures show possible filter locations. NOTE: A duct-
work access door must be used in counterflow applications
to allow filter removal. If the filter rack is used, the side of
the plenum must be at least as tall as dimension "A" shown
in the following illustration. For dimension of "A" refer to the
following chart.
COUNTERFLOW FILTER INSTALLATION
This furnace has provisions for the installation of return air
filters at the counterflow top return. The furnace will
accommodate the following filter sizes depending on cabi-
net size:
"A"
Min
Return Air
Optional
Access
Door
Cabinet
Width
Filter Area
(in
2
)
Qty.
Filter Size
(in)
Dimension "A:
(in)
14 15.1
17 1/2 14.2
21 13.0
24 1/2 11.3
14 20.4
17 1/2 19.7
21 18.8
24 1/2 17.7
14 25.5
17 1/2 25.0
21 24.3
24 1/2 23.4
15x20x1
20x20x1
25x20x1
COUNTERFLOW TOP RETURN
600
800
1000
2
2
2
Refer to Minimum Filter Area tables to determine filter area
requirement. NOTE: Filters can also be installed elsewhere
in the duct system such as a central return.
Horizontal Installations
Filter(s) must be installed external to the furnace casing for
horizontal installations. For most installations it is prefer-
able to use a central return with filters installed in the duct
behind the return air grill. In this way filter replacement is
relatively simple by merely removing the grille, rather than
going into the attic or crawl space.
ADDITIONAL FILTERING ACCESSORIES
Internal Filter Retention Kit
These kits can be used only on 90% furnaces with either
Up-flow installations kit (RF000180) or Down-flow kit
(RF000181). These kits should not be used for Horizontal
installations. See the accessories section of this
manual for more information.
External Filter Rack Kit (EFR01)
The external filter rack kit is intended to provide a location
external to the furnace casing, for installation of a perma-
nent filter on upflow model furnaces. The rack is designed
to mount over the indoor blower compartment area of either
side panel, and provide filter retention as well as a location
for attaching return air ductwork.
Electronic Air Cleaner (ASAS and GSAS) or Media
Air Cleaner (AMU and GMU)
The electronic air cleaner and media air cleaner are multi-
positional high efficiency air filtration devices that can be
installed in any position, except with the access door fac-
ing down. The best location for the air cleaner is in the re-
turn air duct next to the blower compartment. Before install-
ing the air cleaner, consider the application. The electronic
air cleaner must be readily accessible for periodic inspec-
tion and cleaning of the pre-filters and electronic cells while
the media air cleaner must be readily accessible for peri-
odic inspection and replacement of the Media Air Cleaner
(AMU and GMU) filter cartridge (3 per carton) M0-1056, M1-
1056, M2-1056, M8-1056, to maintain maximum efficiency
and trouble-free operation. Carbon Filters 1156-3 and 1856-
3 (set of 3) are also available. See Product Catalog for ex-
act filter for your model.
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