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All installations and services must be performed by qualified service personnel.
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On highboy furnaces, it is necessary to cut the return air opening in the side or rear casing, depending upon the
needs of the specific installation.
The filter rack provided with the furnace, refer to Fig. 5, will serve as a template to scribe a mark for the return air
opening on the casing. Place the filter rack on the casing one inch up from the bottom of the furnace and centered
from side to side. Place the securing flange against the casing when locating the return air opening.
Fig. 5: A typical filter rack and dimensions for the highboy furnaces.
PLEASE NOTE:
While scribing the return air opening, the filter rack can be held in position by tape or similar
temporary means.
Position the open end of the filter rack so as to provide access for filter replacement. Once the filter rack is
positioned correctly, scribe a line along the inside of the securing flange on three of the sides. To scribe a line on the
fourth side (the open end), use the open end support as a guide.
Remove the filter rack and cut the return air opening in the casing. Now the filter rack can be anchored to the furnace
with screws or pop-rivets through the securing flange of the filter rack.
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?WARNING: When cutting openings in the casing DO NOT CUT ANY SUPPORTING
CLIPS OR ANGLES. Cut as close to the scribed line as possible, but do not cut the base clip or
blower pan support angle. (See Fig. 6).
Fig. 6: Cutaway view of fan section of a typical highboy furnace.
Connect the return air plenum to the filter rack and slide the filter into place. Dimensions for adapting the return air
plenum to the filter rack are provided on the bottom of the previous page.