035-20646-001 Rev. A (1004)
Unitary Products Group
5
TABLES 2 AND 3 are to be used as a guide only to help the installer
determine if the duct sizes are large enough to obtain the proper air flow
(CFM) through the furnace. TABLES 2 and 3 ARE NOT to be used to
design ductwork for the building where the furnace is being installed.
There are several variables associated with proper duct sizing that are
not included in the tables. To properly design the ductwork for the build-
ing, Refer to the ASHRAE Fundamentals Handbook, Chapter on
“DUCT DESIGN” or a company that specializes in Residential and Mod-
ular Home duct designs.
IMPORTANT:
If the supply air duct is being connected to the furnace
without the use of an accessory duct connector, then a transition duct
must be installed with flanges or tabs that are securely attach and
sealed to the supply air duct and to the base of the furnace. The transi-
tion duct must have insulation between the transition duct and any com-
bustible material.
The transition duct must be the same dimensional size as the rectangu-
lar opening in the base of the furnace.
Downflow Air Conditioning Coil Cabinet
The Cooling Coil Cabinet can be used in place of the combustible floor
base for downflow installations on combustible materials. The furnace
should be installed with the cooling coil cabinet specifically intended for
downflow applications. The cooling coil cabinet must be secured to the
floor. A supply air duct plenum is installed through the opening pro-
vided. The supply air duct is then secured to the duct system with
screws and sealed to prevent leaks. If a matching cooling coil is used, it
may be placed directly on the furnace outlet using the accessory transi-
tion kit and sealed to prevent leakage. The transition kit must be used to
secure the cooling coil cabinet to the furnace casing when installed in a
downflow configuration.
This transition kit may be installed in one of two ways. The transition kit
may be installed and secured to either the furnace or the cooling coil
cabinet by the use of screws and then it must be sealed to prevent
leaks.
•
If the transition kit has been installed on the cooling coil cabinet it
must be secured to the cooling coil cabinet with screws. The sup-
ply air side of the furnace is then placed on the cooling coil cabi-
net and then sealed for leaks.
•
If the transition kit has been installed on the supply air side of the
furnace it must be secured to the furnace with screws. The fur-
nace and the transition kit are then placed on the cooling coil cab-
inet and then sealed for leaks.
NOTE:
Refer to instructions packed out with coil cabinet, for securing
and sealing to the furnace.
IMPORTANT:
The furnace, transition kit, and the cooling coil cabinet
MUST BE SEALED as needed to prevent leaks, AND SECURED. Refer
to the assembly drawing in Figures 2.
IMPORTANT:
On all installations without a coil, a removable access
panel is recommended in the outlet duct such that smoke or reflected
light would be observable inside the casing to indicate the presence of
leaks in the heat exchanger. This access cover shall be attached in
such a manner as to prevent leaks.
Horizontal Models
Horizontal Installations With a Cooling Coil Cabinet
The furnace should be installed with the cooling coil cabinet specifically
intended for horizontal applications. If a matching cooling coil is used, it
may be placed directly on the supply air side of the furnace and sealed
to prevent leakage. A warm air duct plenum with 1" (2.54 cm) is
installed through the opening provided. The supply air duct system is
connected to the warm air plenum and sealed to prevent leaks.
IMPORTANT:
The furnace, the cooling coil cabinet, and all duct work
MUST BE SEALED as needed to prevent leaks, AND SECURED. Refer
to the assembly drawing in Figure 2.
Attach the supply plenum to the air conditioning coil cabinet outlet duct
flanges through the use of S cleat material when a metal plenum is
used. The use of an approved flexible duct connector is recommended
on all installations. The connection to the furnace, air conditioning coil
cabinet and the supply plenum should be sealed to prevent air leakage.
The sheet metal plenum should be crosshatched to eliminate any pop-
ping of the sheet metal when the indoor fan is energized. The minimum
plenum height is 12" (30.5 cm). If the plenum is shorter than 12" (30.5
cm) the turbulent air flow may cause the limit controls not to operate as
designed, or the limit controls may not operate at all. Also the plastic
drain pan in the under the air conditioning coil can overheat and melt
Refer to the installation instructions supplied with the air conditioning
coil for additional information.
FIGURE 1 :
Combustible Floor Base Accessory
The supply air temperature MUST NEVER exceed the Maximum
Supply Air Temperature, specified on the nameplate.
Operating the furnace above the maximum supply air temperature
will cause the heat exchanger to overheat, causing premature heat
exchanger failure. Improper duct sizing, dirty air filters, incorrect
manifold pressure, incorrect gas orifice and/or a faulty limit switch
can cause the furnace to operate above the maximum supply air
temperature. Refer to sections II, III and XI for additional informa-
tion on correcting the problem.
DOWNFLOW
FURNACE
WARM AIR PLENUM
WITH 1” FLANGES
FIBERGLASS
INSULATION
FIBERGLASS TAPE
UNDER FLANGE
COMBUSTIBLE FLOOR
BASE ACCESSORY
FIGURE 2:
Transition Kit Assembly
AIRFLOW
AIRFLOW
AIRFLOW
AIRFLOW
DOWNFLOW
FURNACE
TRANSITION
KIT
TRANSITION
KIT
COOLING
COIL
CABINET
REFRIGERANT
LINES
DRAIN
CONNECTIONS
