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Leveling Legs (If Desired)
In upflow position with side return inlet(s), leveling legs may be
used. See Fig. 29. Install field- -supplied, 5/16 x 1- -1/2 in. (8 x 38
mm) (max) corrosion- -resistant machine bolts, washers and nuts.
NOTE: Bottom closure must be used when leveling legs are used.
It may be necessary to remove and reinstall bottom closure panel to
install leveling legs. To remove bottom closure panel, see Fig. 24.
To install leveling legs:
1. Position furnace on its back. Locate and drill a hole in each
bottom corner of furnace.
2. For each leg, install nut on bolt and then install bolt with
nut in hole. (Install flat washer if desired.)
3. Install another nut on other side of furnace base. (Install flat
washer if desired.)
4. Adjust outside nut to provide desired height, and tighten in-
side nut to secure arrangement.
5. Reinstall bottom closure panel if removed.
5/ 16
(8mm)
1
3
/
4
(44mm)
(8mm)
5
/
16
(44mm)
1
3/ 4
1
(44mm)
Fig. 29 - - Leveling Legs
Location Relative to Cooling Equipment
The cooling coil must be installed parallel with, or on the
downstream side of the unit to avoid condensation in the heat
exchangers. When installed parallel with the furnace, dampers or
other flow control must prevent chilled air from entering the
furnace. If the dampers are manually operated, they must be
equipped with means to prevent operation of either unit unless the
damper is in the full- -heat or full- -cool position.
Platform Furnace Support
Construct working platform at location where all required furnace
clearances are met. See Table 1 and Fig. 27. For furnaces with
1- -in. (25 mm) clearance requirement on side, set furnace on
non- -combustible blocks, bricks or angle iron. For crawlspace
installations, if the furnace is not suspended from the floor joists,
the ground underneath furnace must be level and the furnace set on
blocks or bricks.
Suspended Furnace Support
The furnace must be supported under the entire length of the
furnace with threaded rod and angle iron. See Fig. 28. Secure
angle iron to bottom of furnace as shown.
Roll- - Out Protection
Provide a minimum 12- -in. x 22- -in. (305 x 559 mm) piece of sheet
metal for flame roll- -out protection in front of burner area for
furnaces closer than 12- -in. (305 mm) above the combustible deck
or suspended furnaces closer than 12- -in. (305 mm) to joists. The
sheet metal MUST extend underneath the furnace casing by 1- -in.
(25 mm) with the door removed.
(8mm)
5/ 16
1
3
/
4
(44mm)
(8mm)
5/ 16
3/ 4
The bottom closure panel on furnaces of widths 17- -1/2- -in. (445
mm) and larger may be used for flame roll- -out protection when
bottom of furnace is used for return air connection. See Fig. 27 for
proper orientation of roll- -out shield.
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
OFFICIALS
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 Table 9- -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
A89014
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.
23
AIR DUCTS
NOTICE
for
ductwork
design
and
performance
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