Filter
Top Products
On the highboy furnace, it is necessary to cut the return air opening in the lower side, or
rear, of the casing depending upon the needs of the specific installation, refer to Figure
3.
Figure 3: Cutaway view of fan section of a typical highboy furnace.
The side casings have each been pre-punched with four (4), square, knockout openings
for use in locating the proper position for the return air filter rack. On the side of the
furnace, where the return air duct will attach, scribe a line connecting the outside edges
of the knockout openings to form a rectangle. Using a punch, or a large screwdriver,
and a hammer, remove the knockouts and cut the return air opening in the casing.
Sheet metal shears, or a power metal cutting tool, will be required to cut the casing.
Position the open end of the filter rack to the front of the furnace to permit access for
filter replacement. Align the filter rack with the rectangular hole and mark the locations
on the casing of the pre-punched mounting holes in the filter rack flange. Drill pilot holes
in the casing and permanently attach the filter rack to the furnace with screws, or pop-
rivets (these fasteners are not included). Connect the return air plenum to the filter rack
and slide the air filter into position.
13