6
CIRCULATING AIR REQUIREMENTS
WARNING:
All return ducts must be secured to the furnace
with sheet metal screws. All return ducts must be
adequately sealed. When return air is provided
through the bottom of the unit, the joint between
the furnace and the return air plenum must be
air tight.
Return air and circulating air ducts must not be
connected to any other heat producing device
such as a fi replace insert, stove, etc. This may
result in fi re, explosion, carbon monoxide
poisoning, personal injury, or property damage.
Plenums & Air Ducts
This unit is designed only for use with a supply and return
duct. Air ducts should be installed in accordance with the
standards of the National Fire Protection Association
Standard for Installation of Air Conditioning Systems
(NFPA 90A), Standard for Installation of Residence Type
Warm Air Heating and Air Conditioning Systems (NFPA
90B), and all applicable local codes. NFPA publications
are available by writing to: National Fire Protection
Association, Batterymarch Park, Quincy, ME 02269 or visit
www.NFPA.org on the web.
• Plenums and air ducts must be installed in accordance
with the Standard for the Installation of Air Conditioning
and Ventilating Systems (NFPA No. 90A) or the
Standard for the Installation of Warm Air Heating and
Air Conditioning Systems (NFPA No. 90B).
• Design the air ducts according to methods described
by the Air Conditioning Contractors of America (ACCA).
• Air ducts must be aluminum, tin plate, galvanized sheet
steel, or other approved materials for outlet or return air
ducts.
• Snap-Lock or Pittsburgh-Lock seams are preferred. All
other types of seams must be made tight to prevent
leakage.
• It is good practice to seal all connections and joints
with industrial grade sealing tape or liquid sealant.
Requirements for sealing ducts vary from region to
region. Consult with local codes for requirements specifi c
to your area.
• Gas piping must not run in or through any of the air duct
system.
• Applicable installation codes may limit the furnace to
installation in a single-story residence only. Furnace
installations other than closet or alcove require ducted
return air systems.
Return Air Connections
Air return to the furnace must have a minimum free area
opening (see Table 1). A return air grille for closet or alcove
installations is available. Acceptable closet installations
with return air entering through an opening in the fl oor
or ceiling of a closet, must meet all of the following
requirements:
• The return air opening, regardless of its location in the
closet, must not be smaller than size specifi ed on unit
data label. If located in the fl oor, the opening must be
provided with a means of preventing its inadvertent
closure by fl at object(s) placed over the opening.
• A return air grille must be used when furnace is installed
in a closet or alcove:
Alcove installations: use return air grille & frame assembly
P/N 902989 or equivalent. See Figure 2, page.
Closet installations: use wall mount return air grilled
P/N 902999 or equivalent.
NOTE:
For 5 ton A.C. or H.P.
system, 155 in
2
(1,000 cm
2
) must be added.
Downfl ow alcove installations: the grille (with frame
provided) may be attached to the top of the furnace and all
paneling and trim fl ushed to it. This installation provides
an access door for future installation of NORDYNE air
conditioning or heat pump coils on top of the furnace.
• Materials located in return air duct system must have
a fl ame-spread classifi cation of 200 or less.
• Noncombustible pans having 1” upturned fl anges must
be located beneath openings in a fl oor-return duct
system.
• Wiring materials located in return duct system must
conform to NEC Article 300-22(c).
• If return air opening is located below top of furnace, a
minimum clearance must be provided between opening
and furnace. See Table 1 (page 5).
Supply Air Connections
• Supply duct system must be designed for proper air
distribution. Static pressure measured externally to
furnace shall not exceed static pressure rating listed
on furnace nameplate.
• Duct system must be designed so that no supply registers
are located in duct system directly below the furnace.
Acoustical Ducts
Certain installations may require the use of acoustical
lining inside the supply duct work.
• Acoustical insulation must be in accordance with the
current revision of the Sheet Metal and Air Conditioning
Contractors National Association (SMACNA) application
standard for duct liners.
• Duct lining must be UL classifi ed batts or blankets with
a fi re hazard classifi cation of FHC-25/50 or less.
• Fiber duct work may be used in place of internal duct
liners if the fi ber duct work is in accordance with the
current revision of the SMACNA construction standard
on fi brous glass ducts. Fibrous duct work and internal
acoustical lining must be NFPA Class 1 air ducts when
tested per UL Standard 181 for Class 1 ducts.
