Ductwork Acoustical Treatment; Supply Air Connections; Return Air Connections; Filter Arrangement - Carrier 58MCB Installation, Start-Up, And Operating Instructions Manual

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.
For a furnace not equipped with a cooling coil, the outlet duct shall
be provided with a removable access panel. This opening shall be
accessible when the furnace is installed and shall be of such a size
that the heat exchanger can be viewed for possible openings using
light assistance or a probe can be inserted for sampling the air
stream. The cover attachment shall prevent leaks.

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
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

Upflow Furnaces
Connect supply-air duct to 3/4-in. flange on furnace supply-air
outlet. The supply-air duct attachment must ONLY be connected
to furnace supply-/outlet-air duct flanges or air conditioning coil
casing (when used). DO NOT cut main furnace casing to attach
supply side air duct, humidifier, or other accessories. All accesso-
ries MUST be connected external to furnace main casing.
Downflow Furnaces
Connect supply-air duct to supply-air opening on furnace. The
supply-air duct attachment must ONLY be connected to furnace
supply/outlet or air conditioning coil casing (when used), when
installed on non-combustible material. When installed on combus-
tible material, supply-air duct attachment must ONLY be con-
nected to an accessory subbase or factory approved air condition-
ing 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. Supply air
opening duct flanges must be modified per Fig. 24.
Horizontal Furnaces
Connect supply-air duct to supply air opening on furnace. The
supply-air duct attachment must ONLY be connected to furnace
supply/outlet or air conditioning coil casing (when used). 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 furnace and its return air system shall be designed and
installed so that negative pressure created by the air circulating fan
cannot affect another appliance's combustion air supply or act to
mix products of combustion with circulating air and the air
circulating fan of the furnace, if installed in an enclosure commu-
nicating with another fuel-burning appliance not of the direct-vent
type, shall be operable only when any door or panel covering an
opening in the furnace fan compartment or in return air plenum on
ducts is in the closed position.
→
Table 4—Filter Information
FURNACE
CASING
Side Return†*
WIDTH (IN.)
17-1/2 (1) 16 X 25 X 1
21 (1) 16 X 25 X 1
24-1/2 (1 or 2) 16 X 25 X 1
* Factory-provided with the furnace. Filters may be field modified by cutting
filter material and support rods (3) in filters. Alternate sizes and additional
filters can be ordered from your distributor or dealer.
† Upflow only. Alternate sizes and additional filters my be ordered from your
dealer.
FIRE HAZARD
A failure to follow this warning could result in fire, personal
injury, or death.
Never connect return-air ducts to the back of the furnace.
Return-air duct connections on furnace side(s) permitted in
upflow applications only.
Upflow Furnaces
The return-air duct must be connected to end, sides (left or right),
or a combination of end and side(s) of main furnace casing as
shown in Fig. 2. Bypass humidifier may be attached into unused
side return air portion of the furnace casing. DO NOT connect any
portion of return-air duct to back of furnace casing.
Downflow and Horizontal Furnaces
The return-air duct must be connected to end inlet opening
provided as shown in Fig. 2. DO NOT cut into casing sides or back
to attach any portion of return-air duct. Bypass humidifier connec-
tions should be made at ductwork or coil casing sides exterior to
furnace.
Step 5—Filter Arrangement
FIRE, CARBON MONOXIDE AND POISONING
HAZARD
Failure to follow this warning could result in fire, personal
injury, or death.
Never operate a unit without a filter or with filter access door
removed.
Factory-supplied washable framed filters are shipped in blower
compartment. Determine location for filter and relocate filter
retaining wire if necessary. See Table 4 to determine correct filter
size for desired filter location. Table 4 indicates filter size,
location, and quantity shipped with this furnace. See Fig. 2 for
location and size of bottom and side return-air openings.
CUT HAZARD
Failure to follow this caution may result in minor personal
injury.
Use care when cutting support rods in filters to protect against
flying pieces and sharp rod ends. Wear safety glasses, gloves,
and appropriate protective clothing.
22
FILTER SIZE (IN.)
FILTER TYPE
Bottom Return*
(1) 16 X 25 X 1
(1) 20 X 25 X 1
(1) 24 X 25 X 1
FRAMED
Cleanable
Cleanable
Cleanable