26
440 01 4201 03
Specifications subject to change without notice.
Figure 31
Accessory Bottom Filter Rack
L10F031
B
A
28
−
7/16
(722.2)
22
−
5/16
(566.4)
2
−
3/16
(55.5)
A
Table 9
Dimensional Drawing
−
inch (mm)
KIT NO.
FURNACE
WIDTH
A
B
NAHB00601FF
17
−
1/2
(444.5)
14
−
5/8
(371.5)
17
−
5/8
(447.7)
NAHB00701FF
21
(533.4)
18
−
1/8
(460.4)
21
−
1/8
(536.6)
NAHB00801FF
24
−
1/2
(622.3)
21
−
5/8
(549.3)
24
−
5/8
(625.5)
Air Ducts
NOTICE
Many states, provinces and localities are considering or have
implemented standards and/or restrictions on duct sizing
practices, ductwork leakage, and/or ductwork thermal, airflow
and electrical efficiencies. CONSULT LOCAL CODE OFFI-
CIALS for ductwork design and performance requirements in
your area.
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 Manual D), 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 external
static pressure. The furnace airflow rates are provided in the
Service and Technical Manual, Air Delivery
−
CFM (with filter).
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 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.
NOTE
: 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.
Return Duct Sizing
Refer to the Filter Selection and Duct Sizing section for
information on the proper selection of filter sizes and the
associated ductwork and duct transitions. Improperly designed
filtering systems and return ductwork are the most common
causes of airflow and/or noise complaints in HVAC systems.
Ductwork Acoustical Treatment
NOTE
: 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.
NOTE
: For horizontal applications, the top most flange may be
bent past 90
to allow the evaporator coil to hang on the
flange temporarily while the remaining attachment and sealing
of the coil are performed.
