23
Table 3 –
Opening Dimensions --- In. (mm)
FURNAC
E
CASING
WIDTH
APPLICATION
PLENUM OPENING
FLOOR OPENING
A
B
C
D
17-1/2
(445)
Upflow Applications
16 (406)
24-1/8 (613)
16-5/8 (422)
24-3/4 (629)
Downflow Applications on Non-Combustible Flooring
15-7/8 (403)
19 (483)
16-1/2 (419)
19-5/8 (498)
Downflow Applications on Combustible Flooring Using KGASB Subbase
Furnace with or without CAP, CAR or CNPV, CNRV Coil Assembly or KCAKC
Coil Box
15-1/8 (384)
19 (483)
16-3/4 (425)
20-3/8 (518)
Downflow Applications on Combustible Flooring NOT Using KGASB
Subbase Furnace with CAP, CAR or CNPV, CNRV Coil Assembly or KCAKC
Coil Box
15-1/2 (394)
19 (483)
16-1/2 (419)
20 (508)
21
(533)
Upflow Applications
19-1/2 (495)
24-1/8 (613)
20-1/8 (511)
24-3/4 (629)
Downflow Applications on Non-Combustible Flooring
19-3/8 (492)
19 (483)
20 (508)
19-5/8 (498)
Downflow Applications on Combustible Flooring Using KGASB Subbase
Furnace with or without CAP, CAR or CNPV, CNRV Coil Assembly or KCAKC
Coil Box
18-5/8 (473)
19 (483)
20-1/4 (514)
20-3/8 (518)
Downflow Applications on Combustible Flooring NOT Using KGASB
Subbase Furnace with CAP, CAR or CNPV, CNRV Coil Assembly or KCAKC
Coil Box
19 (483)
19 (483)
20 (508)
20 (508)
24-1/2
(622)
Upflow Applications
23 (584)
24-1/8 (613)
23-5/8 (600)
24-3/4 (629)
Downflow Applications on Non-Combustible Flooring
22-7/8 (581)
19 (483)
23-1/2 (597)
19-5/8 (498)
Downflow Applications on Combustible Flooring Using KGASB Subbase
Furnace with or without CAP, CAR or CNPV, CNRV Coil Assembly or KCAKC
Coil Box
22-1/8 (562)
19 (483)
23-3/4 (603)
20-3/8 (518)
Downflow Applications on Combustible Flooring NOT Using KGASB
Subbase Furnace with CAP, CAR or CNPV, CNRV Coil Assembly or KCAKC
Coil Box
22-1/2 (572)
19 (483)
23-1/2 (597)
20 (508)
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 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. (25 mm) clearance from combustible materials to
supply air ductwork for a distance of 36 in. (914 mm)
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
(3 M) 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. (19 mm) 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 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 ONLY be connected to furnace
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.
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 that the
air circulating 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 in the closed position.
FIRE HAZARD
Failure to follow this warning could result in personal injury,
death or property damage.
Never connect return-air ducts to the back of the furnace.
Return-air duct connections on furnace side(s) permitted in
upflow applications only.
!
WARNING
58MEC
