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18-CD22D1-5
Installer’s Guide
Association Pamphlet No. 90. They should be sized in accor-
dance 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 exchanger. With
a parallel flow arrangement, the dampers or other means used
to control flow of air shall be adequate 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 material may
be used for return air and discharge connections to prevent
transmission of vibration. Though these units have been specifi-
cally 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 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 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 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 terminating 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 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 50° F.
All return air duct systems should provide for installation of
return air filters.
1. Set the furnace in place.
2. For upflow side return installations, remove the insulation
around the opening in the blower compartment.
3. 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 4 for duct connection dimensions for various fur-
naces.
NOTE:
On upflow 5 ton airflow models, if the airflow requirement
exceeds 1800 CFM, these models will require return air
openings and filters on both sides; OR 1 side and the
bottom; OR just the bottom.
4. 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.
5. If flanges are not required, and a filter frame is installed, cut
between locating notches (See Figure 10).
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