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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.
Table 3—Opening Dimensions (In.)
FURNACE
CASING
WIDTH
APPLICATION
PLENUM OPENING FLOOR OPENING
ABCD
14–3/16
Upflow Applications on Combustible or Noncombustible
Flooring (KGASB subbase not required)
12-11/16 21-5/8 13-5/16 22-1/4
Downflow Applications on Noncombustible Flooring
(KGASB subbase not required)
12-9/16 19 13-3/16 19-5/8
Downflow applications on combustible flooring (KGASB
subbase required)
11-13/16 19 13-7/16 20-5/8
Downflow Applications on Combustible Flooring with CD5 or
CK5 Coil Assembly or KCAKC coil box (KGASB subbase
not required)
12-5/16 19 13-5/16 20
17–1/2
Upflow Applications on Combustible or Noncombustible
Flooring (KGASB subbase not required)
16 21-5/8 16-5/8 22-1/4
Downflow Applications on Noncombustible Flooring
(KGASB subbase not required)
15-7/8 19 16-1/2 19-5/8
Downflow applications on combustible flooring (KGASB
subbase required)
15-1/8 19 16-3/4 20-5/8
Downflow Applications on Combustible Flooring with CD5 or
CK5 Coil Assembly or KCAKC coil box (KGASB subbase
not required)
15-1/2 19 16-1/2 20
21
Upflow Applications on Combustible or Noncombustible
Flooring (KGASB subbase not required)
19-1/2 21-5/8 20-1/8 22-1/4
Downflow Applications on Noncombustible Flooring
(KGASB subbase not required)
19-3/8 19 20 19-5/8
Downflow applications on combustible flooring (KGASB
subbase required)
18-5/8 19 20-1/4 20-5/8
Downflow Applications on Combustible Flooring with CD5 or
CK5 Coil Assembly or KCAKC coil box (KGASB subbase
not required)
19 19 20 20
24-1/2
Upflow Applications on Combustible or Noncombustible
Flooring (KGASB subbase not required)
23 21-1/8 23-5/8 22-1/4
Downflow Applications on Noncombustible Flooring
(KGASB subbase not required)
22-7/8 19 23-1/2 19-5/8
Downflow applications on Combustible flooring (KGASB
subbase required)
22-1/8 19 23-3/4 20-5/8
Downflow Applications on Combustible Flooring with CD5 or
CK5 Coil Assembly or KCAKC coil box (KGASB subbase
not required)
22-1/2 19 23-1/2 20
→ Fig. 14—Duct Flanges
A02329
UPFLO
W OWNFLOW
HORIZONTAL
PREFERRED
PERMITTED
PREFERRED
PREFERRED
PREFERRED
120˚
MIN
PREFERRED
120˚
MIN
PREFERRED
120˚
MIN
90˚
90˚
PERMITTED PERMITTED
D
11