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and outdoor air is used, the ducts and damper system
must be designed so that the return air supply to the
furnace is equal to the return air supply under normal,
indoor return air applications.
furnace blower to provide airflow over the indoor coil,
the coil must be installed downstream (on the outlet
side) of the furnace or in parallel with the furnace.
furnace, a damper must be installed to prevent chilled
air from entering the furnace and condensing on the heat
exchanger. If a manually operated damper is installed,
it must be designed so that operation of the furnace is
prevented when the damper is in the cooling position
and operation of the cooling system is prevented when
the damper is in the heating position.
sealing tape or liquid sealant. Requirements for sealing
ductwork vary from region to region. Consult with local
codes for requirements specific to your area.
Return Air Connections
In applications where the supply ducts carry heated
air to areas outside the space where the furnace is
installed, the return air must be delivered to the furnace
by duct(s) secured to the furnace casing, running full
size and without interruption.
even alignment of furnace (or coil casing) air opening
and return air duct. NOTE: The ductwork must have an
opening equal to that of the return air opening of the
furnace (or coil casing). See
Figure 32 (page 34)
for return air opening size.
Upflow & Horizontal Furnaces
The return air ductwork may be connected to the left
side, right side, or bottom of the furnace. NOTE: If
using the left or right side of the furnace for return air,
the bottom panel (Figure 32) must not be removed from
the bottom of the furnace.
WARNING:
Side Return Installations: To attach the return air duct
to the left or right side of the furnace, punch out the
4 knockouts from the side of the furnace
Using sharp metal cutters, cut an opening between all
Figure 31 (page 33)
or
(Figure
32).
4 knockouts to expose the blower assembly. Position
the return air duct over the opening and secure to the
side with sheet metal screws.
the furnace for return air, the bottom panel
must be removed from the bottom of the furnace. See
page 22
for removal instructions. Position the furnace
over the return air duct and secure together with sheet
metal screws. Make sure the screws penetrate the duct
and furnace casing.
Downflow Furnaces
flanges on the furnace upward 90° with wide duct pliers.
See
Figure 31
for furnace flange locations. NOTE: If
system installation includes AC coil casing, bend the
flanges on the coil casing upward 90° before attaching
the return air duct.
casing (if installed) with sheet metal screws. Make
sure the screws penetrate the sheet metal casing and
flanges.
The supply air must be delivered to the heated space
by duct(s) secured to the furnace or coil box casing,
running full size and without interruption.
To attach the supply air duct to upflow & horizontal
furnaces, bend the flanges on the furnace upward 90°
with wide duct pliers. See
furnace flange locations. NOTE: If system installation
includes AC coil casing, bend the flanges on the coil
casing upward 90° before attaching the supply air duct.
Position the supply air ductwork onto the furnace
ensuring even alignment of furnace air opening and
supply air duct. NOTE: The ductwork must have an
opening equal to that of the supply air opening of the
furnace. See
Figure 31
opening size.
Damping ducts, flexible vibration isolators, or pleated
media-style filters on the return air inlet of the furnace
may be used to reduce the transmission of equipment
noise eminating from the furnace. These treatments can
produce a quieter installation, particularly in the heated
space. However, they can increase the pressure drop in
the duct system. Care must be taken to maintain the proper
maximum pressure rise across the furnace, temperature
rise and flow rate. This may mean increasing the duct size
and/or reducing the blower speed. These treatments must
be constructed and installed in accordance with NFPA and
SMACNA construction standards. Consult with local codes
for special requirements. For best sound performance,
install all the needed gaskets and grommets around
penetrations into the furnace, such as for electrical wiring.
If using the bottom of
(Figure
Figure 32 (page 34)
and
Figure 32
for supply air
32)
for
15
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