Air Ducts; General Requirements; Ductwork Acoustical Treatment; Supply Air Connection - Carrier 58DXT Operating Instructions Manual

AIR FROM INDOOR
58DXT
UNCONFINED
FURNACE
SPACE
HIGH-FIRE
Free Area
INPUT
of Opening
(BTUH)
(Sq In.)
63,000 100
84,000 100
105,000 105
b. If combustion air is taken from outdoors through 2 hori-
zontal ducts, the openings and ducts MUST have at least 1
sq in. of free area per 2000 Btuh of total input for all
equipment within the confined space. (See Fig. 4 and Table
2.)
c. If combustion air is taken from outdoors through a single
opening or duct (horizontal or vertical) commencing within
12 in. of the top of the confined space, opening and duct
MUST have at least 1 sq in. of free area per 3000 Btuh of
the total input for all equipment within the confined space
and not less than the sum of the areas of all vent connectors
in the confined space. (See Fig. 4 and Table 2.) Equipment
clearances to the structure shall be at least 1 in. from the
sides and back and 6 in. from the front of the appliances.
When ducts are used, they must be of the same cross-sectional area
as the free area of the openings to which they connect. The
minimum dimension of ducts must not be less than 3 in. (See Fig.
4.)
→
Step 3—Air Ducts

GENERAL REQUIREMENTS

The duct system should be designed and sized according to
accepted national standards such as those published by: Air
Conditioning Contractors Association (ACCA), Sheet Metal and
Air Conditioning Contractors National Association (SMACNA) or
American Society of Heating, Refrigerating and Air Conditioning
Engineers (ASHRAE) or consult factory The Air Systems Design
Guidelines reference tables available from your local distributor.
The duct system should be sized to handle the required system
design CFM at the design static pressure.
When a furnace is installed so that the supply ducts carry air to
areas outside the space containing the furnace, the return air must
also be handled by a duct(s) sealed to the furnace casing and
terminating outside the space containing the furnace.
Secure ductwork with proper fasteners for type of ductwork used.
Seal supply- and return-duct connections to furnace with code
approved tape or duct sealer.
Flexible connections should be used between ductwork and
furnace to prevent transmission of vibration. Ductwork passing
through unconditioned space should be insulated to enhance
system performance. When air conditioning is used, a vapor
barrier is recommended.
Maintain a 1-in. clearance from combustible materials to supply air
ductwork for a distance of 36 in. horizontally from the furnace. See
NFPA 90B or local code for further requirements.

DUCTWORK ACOUSTICAL TREATMENT

Metal duct systems that do not have a 90 degree elbow and 10 ft
of main duct to the first branch take-off may require internal
acoustical lining. As an alternative, fibrous ductwork may be used
Table 2—Minimum Free Area Of Combustion Air Opening
OUTDOOR AIR THROUGH
VERTICAL DUCTS
Free Area of
Opening and Duct
(Sq In.)
15.8
21.0
26.3
OUTDOOR AIR THROUGH
HORIZONTAL DUCTS
Round Free Area of
Pipe Opening and Duct
(In. Dia) (Sq In.)
5 31.5
6 42.0
6 52.5
if constructed and installed in accordance with the latest edition of
SMACNA construction standard on fibrous glass ducts. Both
acoustical lining and fibrous ductwork shall comply with NFPA
90B as tested by UL Standard 181 for Class 1 Rigid air ducts.
SUPPLY AIR CONNECTIONS
Connect supply-air duct to supply-air opening on furnace. The
supply-air duct attachment must ONLY be connected to fur-
nace supply/outlet or air conditioning coil casing (when used),
when installed on non-combustible material. When installed on
combustible material, supply-air duct attachment must ONLY
be connected to an accessory subbase or factory approved air
conditioning coil casing. DO NOT cut main furnace casing to
attach supply side air duct, humidifier, or other accessories. All
accessories MUST be connected external to furnace main
casing.

RETURN AIR CONNECTIONS

The return-air duct must be connected to return-air opening
provided as shown in Fig. 1. DO NOT cut into casing sides or
back to attach any portion of return-air duct. Bypass humidifier
connections should be made at ductwork or coil casing sides
exterior to furnace.
Step 4—Supply-Air Plenum Installation

DOWNFLOW INSTALLATION

NOTE: This furnace is approved for use on combustible flooring
when manufacturer's
KGASB0201ALL is used. Manufacturer's accessory floor base is
not required when this furnace is installed on manufacturer's Coil
Assembly Part No. CD5 or CK5, or Coil Box Part No. KCAKC is
used.
1. Determine application being installed from Table 3.
2. Construct hole in floor per dimensions specified in Table 3
and Fig. 5.
3. Construct plenum to dimensions specified in Table 3.
4. If downflow subbase (KGASB) is used, install as shown in
Fig. 6.
If coil assembly CD5, CK5, or Coil Box KCAKC is used,
install as shown in Fig. 7.

INSTALLATION ON COMBUSTIBLE FLOOR

1. Cut and frame hole in floor per dimensions in Installation
Instructions packaged with downflow subbase.
2. When completed, downflow subbase, plenum, and furnace (or
coil casing when used) should be installed as shown in Fig. 6.
6
OUTDOOR AIR THROUGH
SINGLE DUCT
Round Free Area of
Pipe Opening and Duct
(In. Dia) (Sq In.)
7 21.0
8 28.0
9 35.0
accessory floor base
Round
Pipe
(In. Dia)
6
6
7
Part No.