Service Guide
SYSTEM OPERATION
24
a media air lter or electronic air cleaner can be used as
the requested lter. Refer to the following minimum lter
requirement charts for determination of the minimum lter
area to ensure proper unit performance.
This furnace has provisions for the installation of return air
lters at the counterow top return. Refer to Minimum Filter
Area tables to determine lter area requirement.
Filters can also be installed elsewhere in the duct
system such as a central return.
Filter(s) must be installed external to the furnace casing for
horizontal installations. For most installations it is preferable
to use a central return with lters installed in the duct behind
the return air grill. In this way lter replacement is relatively
simple by merely removing the grille, rather than going into
the attic or crawl space.
The external lter rack kit is intended to provide a location
external to the furnace casing, for installation of a permanent
lter on upow model furnaces. The rack is designed to mount
over the indoor blower compartment area of either side panel,
and provide lter retention as well as a location for attaching
return air ductwork.