Air Ducts; General Requirements; Ductwork Acoustical Treatment; Supply Air Connections - Carrier Series 100 Installation, Start-Up, And Operating Instructions Manual

PERFORATED
DISCHARGE DUCT
FLANGE
Fig. 24—Duct Flanges
Step 4—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 The Air Systems Design Guide-
lines 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
circulated by the furnace to areas outside the space containing the
furnace, the return air shall 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.
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 18 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.
NO
YES
210°
MIN
YES
A93029

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 be connected to
ONLY 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
accessories 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 be connected to ONLY 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 be connected to
ONLY 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. 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 be connected to ONLY 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. The air circulat-
ing fan of the furnace, if installed in an enclosure communicating
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 a return air plenum on ducts
is in the closed position.
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 bottom, sides (left or
right), or a combination of bottom 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.
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