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18-CD19D8-18
Installer’s Guide
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8
DUCT CONNECTIONS
Air duct systems should be installed in accordance with
standards for air conditioning systems, National Fire Protec-
tion 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 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
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 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 CONNECTION
NOTE:
On upflow 5 or 6 ton airflow models where the airflow
requirement exceeds 1800 CFM - Models will require
return air openings and filters on: (1) both sides; or (2)
one side and the bottom; or (3) just the bottom.
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 connect to the existing supply and return
ductwork.
2. For side return installations on upflow models, 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 furnaces.
