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60° F (15° C) during operation. If a combination of indoor
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.
• When a cooling system is installed which uses the
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.
• If a cooling system is installed in parallel with the
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.
• It is good practice to seal all connections and joints
with industrial grade 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. Do not use the back of
the furnace for return air.
• Position the furnace with the return air ductwork ensuring
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
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
the bottom of the furnace.
WARNING:
The bottom panel of the furnace must be in
place when the furnace is installed with side
return air ducts. Removal of all or part of the
base could cause circulation of combustible
products into the living space and create
potentially hazardous conditions, including
carbon monoxide poisoning that could result
in personal injury or death.
• Side Return Installations: To attach the return air duct to
theleftorrightsideofthefurnace,punchoutthe4knockouts
from the side of the furnace
Figure 28 (page 32)
28) must not be removed from
(Figure 28 (page
Using sharp metal cutters, cut an opening between all
4 knockouts to expose the blower assembly. Position
the return air duct over the opening and secure to the
side with sheet metal screws.
• Bottom Return Installations: If using the bottom of
the furnace for return air, the bottom panel
must be removed from the bottom of the furnace. See
page 20
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
• To attach the return air duct to the downflow furnace,
bend the flanges on the furnace upward 90° with wide
duct pliers. See
locations. NOTE: If system installation includes AC coil
casing, bend the flanges on the coil casing upward 90°
before attaching the return air duct.
• Secure the return air ductwork to the furnace or coil
casing (if installed) with sheet metal screws. Make
sure the screws penetrate the sheet metal casing and
flanges.
Supply Air Connections
• 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
for
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 28 for supply air opening size.
Acoustical Treatments
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, be sure to install all the needed gaskets and
grommets around penetrations into the furnace, such as
for electrical wiring
32).
Figure 28 (page 32)
for furnace flange
Figure 28 (page 32)
(Figure
28)
for
15
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