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Ductwork—Airflow
WARNING
Goodman 68
Never allow the products of combustion, including carbon
monoxide, to enter the return ductwork or circulation air
supply.
Duct systems and register sizes must be properly designed
for the CFM and external static pressure rating of the furnace.
Design the ductwork in accordance with the recommended
methods of "Air Conditioning Contractors of America"
Manual D.
Install the duct system in accordance with Standards of the
National Board of Fire Underwriters for the Installation of Air
Conditioning, Warm Air Heating and Ventilating Systems.
Pamphlets No. 90A and 90B.
A closed return duct system must be used with the return
duct connected to the furnace.
NOTE: Ductwork must never be attached to the back of the
furnace.
For installations requiring more than 1,800 CFM, use either
2 side returns or bottom return.
Flexible joints may be used for supply and return connections
to reduce noise transmission.
To prevent the blower from interfering with combustion air or
draft when a central return is used, a connecting duct must
be installed between the unit and the utility room wall.
Never use a room, closet or alcove as a return air chamber.
The furnace is shipped with the top flanges in the flat
position. Before installing a coil or ducts, the flanges must be
bent 90 degrees.
When the furnace is installed with a cooling unit, the furnace
should be installed in parallel with or on the upstream side of the
cooling unit to avoid condensation in the heating element. With a
parallel flow arrangement, the dampers or other means used to
control the flow of air must 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 the full heat or cool position.
When the furnace is installed without a cooling unit, it is
recommended that a removable access panel be provided in the
outlet air duct. This opening shall be accessible when the furnace
is installed and shall be of such a size that the heat exchanger
can be viewed for visual light inspection or such that a sampling
probe can be inserted into the airstream. The access panel must
be made to prevent air leaks when the furnace is in operation.
NOTE: In a horizontal installation, the air conditioning coil must
be adequately supported by proper brackets and supports.
Inadequate coil support can result in furnace cabinet distortion
and air leakage.
CIRCULATING AIR AND FILTERS
When the furnace is heating, the temperature of the return air
entering the furnace must be between 55°F and 100°F (13ºC and
38ºC).
When a furnace is installed so that 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 sealed
to the furnace casing and terminating outside the space
containing the furnace.
Filters—Read this Section Before Installing the
Return Air Ductwork
Filters must be used with this furnace. Discuss filter maintenance
with the building owner. Filters are not ship with this furnace, but
must be provided by the installer. Filters must comply with UL900
or CAN/ULCS111 standards. If the furnace is installed without
filters, the warranty will be voided.
NOTE: An undersized opening will cause reduced airflow. The
bottom return is set up as a knockout.
Upright Installations
Depending on the installation and/or customer preference,
differing filter arrangements can be applied. Filters can be
installed in the central return register, in a side panel external filter
rack kit (upflows) or in the ductwork above a downflow furnace.
As an alternative, a media air filter or electronic air cleaner can be
used as the primary filter.
Circulation Air Filters
One of the most common causes of a problem in a forced air
heating system is a blocked or dirty filter. Circulating air filters
must be inspected monthly for dirt accumulation and replaced if
necessary. Failure to maintain clean filters can cause premature
heat exchanger failure.
A new home may require more frequent replacement until all
construction dust and dirt is removed. Circulating air filters are to
be installed in the return air duct external to the furnace cabinet.
Minimum Filter Sizes for Disposable Filters—Disposable
Nominal 300 F.M. Face Velocity
Furnace Input
70M
90M
115M
Horizontal Installations
Filters must be installed in either the central return register or in
the return air ductwork.
Filter Size (sq. in.)
768
960
1,022
21
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