10 18-CD33D1-4
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 whichever 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 ex-
changer. With a parallel flow arrangement, the dampers
or other means used to control flow of air shall be ade-
quate to prevent chilled air from entering the furnace, 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 pre vent transmission of vibration. Though these units
have been specifically designed for quiet, vibration free op-
eration, air ducts can act as sounding boards and could,
if poorly installed, amplify the slightest vibration to the an-
noyance level.
When the furnace is located in a utility room adjacent to
the living area, the system should be carefully designed
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 locat-
ed 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 installation 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 terminat-
ing outside the space containing the furnace.
RETURN AIR DUCT SYSTEMS
Where there is no complete return duct system, the
return connection must be run full size from the fur-
nace 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 installation
of return air filters.
PREPARATION FOR UPFLOW BOTTOM AND SIDE
RETURN AIR FILTER INSTALLATION
All return air duct systems should provide for installation
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 is shipped in either the bottom or
side location. Remove the filter by first turning the
two latches on the blower door and tilting the door
forward to remove. Remove the filter by sliding it out.
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 locat-
ing 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 dimen-
sions 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 re-
moved for bottom return air. After removing the filter,
lay the furnace on its back. Remove the two 5/16"
hex screws securing the front of the bottom chan-
nel 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 reinstall the two 5/16” screws.
8. The filter retainer is factory supplied for upflow bot-
tom return. Use the filter retainer on side or bottom if
filter is to be used within the furnace cabinet on up-
flow only installations.
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