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10 18-CD22D1-8
Installer’s Guide
DUCT CONNECTIONS
Air duct systems should be installed in accordance with
standards for air conditioning systems, National Fire
Protection Association Pamphlet No. 90. They should
be sized in accordance with ACCA Manual D or which-
ever is applicable.
Central furnaces, when used in connection with cooling
units, shall be installed in parallel or on the upstream
side of the cooling coil to avoid condensation in the heat
exchanger. With a parallel flow arrangement, the damp-
ers or other means used to control flow of air shall be
adequate to prevent chilled air from entering the fur-
nace, and if manually operated, must be equipped with
means to prevent operation of either unit unless the
damper is in full heat or cool position.
On any job, flexible connections of nonflammable mate-
rial may be used for return air and discharge connections
to prevent transmission of vibration. Though these units
have been specifically designed for quiet, vibration free
operation, air ducts can act as sounding boards and could,
if poorly installed, amplify the slightest vibration to the
annoyance level.
When the furnace is located in a utility room adjacent
to the living area, the system should be carefully de-
signed with returns to minimize noise transmission
through the return air grille. Although these furnaces
are designed with large blowers operating at moderate
speeds, any blower moving a high volume of air will
produce audible noise which could be objectionable
when the unit is located very close to a living area. It is
often advisable to route the return air ducts under the
floor or through the attic. Such design permits the in-
stallation of air return remote from the living area
(i.e. central hall).
When the furnace is installed so that the 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(s) sealed to the furnace and termi-
nating outside the space containing the furnace.
RETURN AIR DUCT SYSTEMS
Where there is no complete return duct system, the re-
turn connection must be run full size from the furnace
to a location outside the utility room, basement, attic,
or crawl space.
Do Not install return air through the back of the furnace
cabinet
Do Not install return air through the side of the furnace
cabinet on horizontal applications.
NOTE:
Minimum return air temperature is 55° F.
All return air duct systems should provide for installa-
tion of return air filters.
PREPARATION FOR UPFLOW BOTTOM AND SIDE
RETURN AIR FILTER INSTALLATION
All return air duct systems should provide for installa-
tion of return air filters.
1. Determine the appropriate position to set the
furnace in order to existing supply and return
ductwork.
2. The return air filter and rack are shipped in either
the bottom or side location. Remove the filter and
filter rack by first turning the two latches on the
blower door and tilting the door forward to remove.
Remove the filter by sliding it out of the rack.
Compress the spring loaded filter rack to disengage
the retaining pins/screws from the furnace sides
and slide the filter rack out.
The filter rails are spring loaded for automatic
adjustment to allow standard size, locally obtainable
replacement filters. The filter rack itself slides to
adjust to the required width needed for bottom or
side return.
3. For upflow side return installations, remove the
insulation around the opening in the blower compart-
ment.
4. The side panels of the upflow furnace include
locating notches that are used as guides for cutting
an opening for return air, refer to Figure 10 and the
outline drawing on page 5 for duct connection
dimensions for various furnaces.
5. If a 3/4" flange is to be used for attaching the air
inlet duct, add to cut where indicated by dotted
lines in Figure 10. Cut corners diagonally and bend
outward to form flange.
6. If flanges are not required, and a filter frame is
installed, cut between locating notches (See Figure
10).
7. The bottom panel of the upflow furnace must be
removed for bottom return air. After removing the
filter and filter rack, lay the furnace on its back.
Remove the two 5/16" hex screws securing the front
of the bottom channel to the cabinet. Rotate the
channel downward (or remove by lowering the front
edge of the channel and pulling forward). Slide the
bottom return air panel out of the cabinet. Rotate
the front channel to its original position and rein-
stall the two 5/16” screws.
8. The filter retainer is factory supplied for upflow bot-
tom return. Use the filter retainer on side or bot-
tom if filter is to be used within the furnace cabinet
on upflow only installations.