129098-UIM-G-0411
4
Johnson Controls Unitary Products
SECTION II: DUCTWORK
DUCTWORK GENERAL INFORMATION
The duct system’s design and installation must:
1.
Handle an air volume appropriate for the served space and within
the operating parameters of the furnace specifications.
2.
Be installed in accordance with standards of NFPA (National Fire
Protection Association) as outlined in NFPA pamphlets 90A and
90B (latest editions), in Canada CAN/CGA-B149.1-00 Natural Gas
and Propane Installation Code. or applicable national, provincial,
or state, and local fire and safety codes.
3.
For Manufacture (Mobile) Home and Modular Home Return
Duct System Installations:
The return air duct and the return air plenum are not required by
the furnace manufacturer, provided a return air duct and plenum
are not required by state, local, or regional codes. The only vent
system that is approved for use on this furnace is a Roof Jack
which is a Sealed Combustion Direct Vent System.
4.
Complete a path for heated or cooled air to circulate through the
air conditioning and heating equipment and to and from the condi-
tioned space.
When the furnace is used in conjunction with a cooling coil, the coil
must be installed parallel with, or in the supply air side of the furnace to
avoid condensation in the primary heat exchanger. When a parallel flow
arrangement is used, dampers or other means used to control airflow
must be adequate to prevent chilled air from entering the furnace. If
manually operated, the damper must be equipped with means to pre-
vent the furnace or the air conditioner from operating unless the damper
is in full heat or cool position.
The duct system is a very important part of the installation.
If the duct
system is improperly sized the furnace will not operate properly.
The ducts attached to the furnace plenum, should be of sufficient size
so that the furnace operates at the specified external static pressure
and within the air temperature rise specified on the nameplate.
1.
Cut a rectangular opening in the plenum base.
2.
A sheet metal plate can be made that completely covers the open-
ing in the base.
3.
The plate must be secured with screws.
4.
This plate must be sealed to prevent leaks.
TABLE 1:
Unit Clearances to Combustibles
Application
Top
Front
Rear
Sides
Roof Jack Flue
Floor
1
Duct
1
Closet
Alcove
Closet
Alcove
Closet
Alcove
Closet
Alcove
Closet
Alcove
Closet
Alcove
Closet
Alcove
In. (cm) In. (cm) In. (cm)
In. (cm)
In. (cm) In. (cm) In. (cm) In. (cm) In. (cm) In. (cm) In. (cm) In. (cm) In. (cm) In. (cm)
Downflow
2(50.8)
2(50.8) 6(15.24) 24(60.96)
0
0
0
0
0
0
0
0
0
0
1. Approved duct connector required for use on combustible floor.
FIGURE 1:
Furnace Dimensions
DGAH Series
DGAA Series
A
B
C
D
E
F
G
B
C
D
E
F
G
C
D
E
F
G
Inches
59-1/2”
76”
24.3/4”
23”
19-1/2”
9-3/4”
12”
c.m.
151.0
193.0
62.9
58.4
49.5
24.8
30.5
A
The cooling coil must be installed in the supply air duct, down-
stream of the furnace. Cooled air may not be passed over the heat
exchanger, and must comply with (H.U.D.) TITLE 24, PART
3280.709
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 Table
4 for static pressures.
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.
HAZARD OF ASPHYXIATION, DO NOT COVER OR RESTRICT
FLOOR OPENING.
Fabricate and install an inspection door in the plenum base below
the unit to allow an annual inspection of the heat exchangers. The
inspection door can be fabricated by the following method.