6
CIRCULATING AIR REQUIREMENTS
WARNING:
with sheet metal screws. All return ducts must
air tight.
connected to any other heat producing device
such as a fireplace insert, stove, etc. This may
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 visiting www.NFPA.org.
• Plenumsandairductsmustbeinstalledinaccordance
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).
• Designtheairductsaccordingtomethodsdescribed
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-LockorPittsburgh-Lockseamsarepreferred.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
specific to your area.
• Gaspiping mustnotruninorthroughanyof the air
duct system.
• Applicableinstallationcodesmaylimitthefurnaceto
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 (page 5). A return air grille for
closet or alcove installations is available. Acceptable
closet installations with return air entering through an
opening in the floor or ceiling of a closet, must meet all
of the following requirements:
• Thereturnairopening,regardlessofitslocationinthe
closet, must not be smaller than size specified on unit
data label. If located in the floor, the opening must be
provided with a means of preventing its inadvertent
closure by flat 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 7).
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.
Downflow alcove installations: the grille (with frame
provided) may be attached to the top of the furnace
and all paneling and trim flushed to it. This installation
provides an access door for future installation of
NORDYNE air conditioning or heat pump coils on top
of the furnace.
• Materialslocatedinreturnairductsystemmusthave
a flame-spread classification of 200 or less.
• Noncombustible pans having 1” upturned anges
must be located beneath openings in a floor-return
duct system.
• Wiring materials located in return duct system must
conform to NEC Article 300-22(c).
• Ifreturnairopeningis located belowtop of furnace,
a minimum clearance must be provided between
opening and furnace. See Table 1.
Supply Air Connections
• Supplyduct system mustbedesignedforproper 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.
• DuctliningmustbeULclassiedbattsorblanketswith
a fire hazard classification of FHC-25/50 or less.
• Fiberductworkmaybeusedinplaceofinternalduct
liners if the fiber duct work is in accordance with the
current revision of the SMACNA construction standard
on fibrous 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.
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