5894307-UIM-B-0920
4
Johnson Controls Ducted Systems
*24 in. clearance in front and 18 in. on side recommended for service access.
Note:
All furnaces are approved for alcove and attic installation.
SECTION II: DUCTWORK
DUCTWORK GENERAL INFORMATION
The duct system’s design and installation must:
• Handle an air volume appropriate for the served space and within
the operating parameters of the furnace specifications.
• Be installed in accordance with National Fire Protection Associa-
tion as outlined in NFPA standard 90B (latest editions) or applica-
ble national, provincial, state, and local fire and safety codes.
• Create a closed duct system. When a furnace is installed so the
supply ducts carry air circulated by the furnace to areas outside
the space containing the furnace, the return air must also be han-
dled by a duct or ducts sealed to the furnace casing and terminat-
ing outside the space containing the furnace.
• Complete a path for heated or cooled air to circulate through the
air conditioning and heating equipment and to and from the con-
ditioned space.
When the furnace is used with an indoor coil, the coil must be installed
parallel with, or in the supply air side of the furnace to avoid condensa-
tion in the primary heat exchanger. When a parallel flow arrangement is
used, dampers or other means used to control airflow must be ade-
quate to prevent chilled air from entering the furnace. If manually oper-
ated, the damper must be equipped with means to prevent the furnace
or the air conditioner from operating unless the damper is in full heat or
cool position.
When replacing an existing furnace, if the existing plenum is not the
same size as the new furnace, the existing plenum must be removed
and a new plenum installed that is the correct size for the new furnace.
If the plenum is shorter than 12 in. (30.5 cm) the turbulent airflow may
cause the limit controls not to operate as designed, or the limit controls
may not operate at all.
The duct system is a very important part of the installation.
If the duct
system is incorrectly sized, the furnace does not operate correctly.
The ducts attached to the furnace plenum must be of sufficient size so
the furnace operates at the specified external static pressure and within
the air temperature rise specified on the nameplate.
If a matching cased indoor coil is used, it can be placed directly on the
furnace outlet and sealed to prevent leakage. If an uncased indoor coil
with a thermoplastic drain pan is installed in the upflow/horizontal con-
figuration, an extra 2 in. minimum spacing may be needed to ensure
against drain pan distortion.
On all installations without a coil, a removable access panel is recom-
mended 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 must be attached in such a manner
as to prevent leaks.
DUCT FLANGES
Four flanges are provided to attach ductwork to the furnace. These
flanges are rotated down for shipment. To use the flanges, do the fol-
lowing:
1. Remove the screw holding an individual flange.
2. Rotate the flange so it is in the upward position.
3. Reinstall the screw.
4. Repeat Steps 1 to 3 for all four flanges.
If the flanges are not used, they must remain in the rotated down posi-
tion as shipped.
DUCTWORK INSTALLATION AND SUPPLY PLENUM
CONNECTION
Attach the supply plenum to the furnace outlet. Use an
approved flexible duct connector for all installations. Seal
this connection to prevent air leakage. The sheet metal
must be crosshatched to eliminate any popping of the sheet
metal when the indoor fan is energized.
INDOOR COIL INSTALLATION
The indoor coil must be mounted on the supply side of the furnace as
shown in Figure 2. Refer to the installation instructions provided with
each indoor coil.
Table 1:
Unit Clearances to Combustibles
Application
Upflow
Horizontal
Top
1 in.
0 in.
Vent
0 in.
0 in.
Rear
0 in.
0 in.
Side
0 in.
1 in.
Front*
0 in.
0 in.
Floor
Combustible
Combustible
Closet
Yes
Yes
Line Contact
No
Yes
CAUTION
The indoor coil must be installed in the supply air duct, downstream of
the furnace. Cooled air may not be passed over the heat exchanger.
IMPORTANT:
The minimum plenum height is 12 in. (30.5 cm). The
furnace does not operate correctly on a shorter plenum height. The
minimum recommended rectangular duct height is 4 in. (10.1 cm)
attached to the plenum.
!
WARNING
The duct system must be properly sized to obtain the correct airflow
for the furnace size that is being installed.
Refer to the furnace rating plate for the correct rise range and static
pressures or to Table 4 for the correct rise range.
If the ducts are undersized, the result will be high duct static pres-
sures and/or high temperature rises which can result in a heat
exchanger OVERHEATING CONDITION. This condition can result in
premature heat exchanger failure, which can result in personal injury,
property damage, or death.
Figure 1:
Duct Attachment
IMPORTANT:
On all installations without an indoor 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 must be
attached in such a manner as to prevent leaks.
!
Factory
installed
For duct attachment,
if needed.
