-- 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, 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, 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, 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, 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, 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, CNPV, CNRV Coil Assembly or KCAKC Coil
Box
22-1/2 (572)
19 (483)
23-1/2 (597)
20 (508)
NO
YES
YES
PERFORATED
DISCHARGE DUCT
FLANGE
210 DEG.
MIN
A93029
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 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
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.(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
(3.0 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 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.
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 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.
