11
CIRCULATING AIR REQUIREMENTS
WARNING:
•
Do not allow combustion products to enter the
circulating air supply. Failure to prevent the
circulation of combustion products into the
living space can create potentially hazardous
conditions including carbon monoxide
poisoning that could result in personal injury
or death.
•
All return ductwork must be secured to
the furnace with sheet metal screws. For
installations in confi ned spaces, all return
ductwork must be adequately sealed. When
return air is provided through the bottom of
the furnace, the joint between the furnace and
the return air plenum must be air tight.
•
The surface that the furnace is mounted on must
provide sound physical support of the furnace
with no gaps, cracks or sagging between the
furnace and the fl oor or platform.
•
Return air and circulating air ductwork must
not be connected to any other heat producing
device such as a fi replace insert, stove, etc.
This may result in fi re, explosion, carbon
monoxide poisoning, personal injury, or
property damage.
Plenums and Air Ducts
• Supply and return air must be delivered to the furnace
by duct(s) secured to the furnace casing, running full
size and without interruption.
• Table 8 (pages 26 & 27) contains the maximum airfl ow
and temperature rise data for each furnace input rate.
NOTE:
If the maximum airfl ow is 1,600 CFM or more, it
is recommended that two openings be used for return
air on upfl ow furnaces.
• It is recommended that the outlet duct contain a
removable access panel that is accessible when the
furnace is installed in service. The opening shall be of
a size that smoke or refl ected light may be observed
inside the casing to indicate the presence of leaks in
the heat exchanger. The cover for the opening shall be
attached in such a manner as to prevent leaks.
• If outside air is used as return air to the furnace for
ventilation or to improve indoor air quality, the system
must be designed so that the return air is not less than
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.
• If a cooling system is installed which uses the furnace
blower to provide airfl ow 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 the furnace will not operate
when the damper is in the cooling position or when in
heating position, the cooling system is inoperable.
• 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 specific
requirements.
Supply Air Connections
To attach the supply air duct to the furnace, bend the
furnace fl anges (Figure 25, page 25) upward 90° with wide
duct pliers. Position the duct on top of the furnace and
secure together with sheet metal screws. The screws must
penetrate the sheet metal casing and furnace fl ange.
Return Air Connections
For upfl ow installations, the return air ductwork may be
connected to the left side, right side, or bottom. The bottom
panel (Figure 25) must be installed for left or right return
air.
Do not use the back of the furnace for return air.
Side Return Installations
WARNING:
The solid base of the furnace must be in
position 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.
To attach the return air duct to the left or right side of the
furnace, punch out the four knockouts (Figure 25) from the
preferred side of the furnace. Using sharp metal cutters,
cut an opening between all four knockouts to expose
the blower assembly. Position the return air duct over
the opening in the side and secure together with sheet
metal screws. The screws must penetrate the duct and
furnace cabinet.
Bottom Return Installations
The bottom panel (Figure 25) must be removed from
the bottom of the furnace for bottom return air. Refer to
page 13 for removal instructions. Position the furnace
over the return air duct and secure together with sheet
metal screws. The screws must penetrate the duct and
furnace cabinet.
