129098-UIM-G-0411
Johnson Controls Unitary Products
5
DUCTWORK INSTALLATION
Air Distribution Systems
For proper air distribution, the supply duct system shall be designed so
that the static pressure does not exceed the listed static pressure rating
on the furnace rating plate.
Three typical distribution systems are illustrated in Figure 2.
Location, size and number of registers should be selected on the basis
of best air distribution and floor plan of the home.
The Air Temperature Rise is to be adjusted to obtain a temperature rise
within the range(s) specified on the furnace rating plate.
DUCT DESIGN - CANADA
Supply duct design shall be in accordance with the latest HRA Digest,
the ASHRAE Handbook Fundamentals, or other good engineering prin-
ciples.
NOTE:
Refer to HRA Digest Residential Air System Design Manual,
Sections 5 and 6, the requirements of which are summarized as fol-
lows:
1.
The kilowatt output of each duct register shall not exceed 2.35 kW.
2.
The furnace output should not be more than 20% greater than the
calculated heat loss of the home. If a larger furnace is used, the
duct system shall be capable of the increased air volumes neces-
sary to maintain a maximum air temperature rise of 50
o
C as the
air passes over the furnace heat exchanger.
3.
At least one warm air supply outlet shall be provided in each room.
4.
When rooms are located adjacent to the exterior walls, warm air
outlets shall be located so as to bathe at least one exterior wall
and, where practical, a window area with warm air, except for bath-
rooms or kitchens where this might not be practical.
5.
Where practical, outlets shall be provided near the exterior doors
of the home.
CLEARANCE REQUIREMENTS - CANADA
Supply air ducts from warm air furnaces having a specified minimum
plenum clearance shall maintain this clearance from combustible mate-
rial for at least the distance specified in CSA Standards C22.2 No. 23 or
B140.10 or CGA Standard CAN/CGA-2.3.
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.
FIGURE 2:
Air Distribution Systems
A
Single trunk duct
Dual trunk duct
Transition duct
1
B*
Dual trunk duct with crossover connector
Crossover
C
Transition Duct with Branches
Branches
3
1. Crossover Duct must be centered directly under furnace.
2. Use 12” (30.5 cm) Diameter Round or insulated Flex-duct only.
3. Terminate Flex-duct (opposite furnace) in the center of the trunk duct.
4. Flex-duct material must be pulled tight — No Loops or unnecessary dips — Air Flow may be impeded.
4
2
FIGURE 3:
Closet To Door Clearance - 5” or Greater
5 in (12.7 cm) or greater * Closet
to Door Clearance
Furnace to Closet Door Clearance —
5 Inches (12.7 cm) or more
1.
2.
Return Air Grille Part No.
7900-287P/A * White
The closet door
have a minimum of
of free area in the upper half of the door.
MUST
250 Inches (1613 cm )
2
2
250 IN. (161 cm )
MINIMUM
FREE AREA
2
2
50 IN. (322 cm )
MINIMUM
FREE AREA
2
2
250 IN. (161 cm )
MINIMUM
FREE AREA
2
2
B
CLOSET
DOOR
FURNACE
A
If opening for return air is located in the floor or sidewalls and
below the top of the furnace casing:
Return Air Closet Door Part No.
7900-7771/C* White
6 inches (15.2 cm) minimum clearance must be maintained from
the front of furnace.
6 inches (15.2 cm) minimum clearance must be provided on side
where return is located, and