7
CIRCULATING AIR REQUIREMENTS
WARNING:
Do not allow combustion products to enter the
circulating air supply. Failure to prevent the
circulation of combustion products into the
living space can create potentially hazardous
conditions including carbon monoxide poison-
ing that could result in personal injury or death.
All return ductwork must be secured to
the furnace with sheet metal screws. For
installations in confi ned spaces, all return
ductwork must be adequately sealed. The joint
between the furnace and the return air plenum
must be air tight.
The surface that the furnace is mounted on must
provide sound physical support of the furnace
with no gaps, cracks or sagging between the
furnace and the fl oor or platform.
Return air and circulating air ductwork 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.
Return Air Connections
U.S.A. home manufacturers shall comply with all of the
following conditions to have acceptable return air systems
for closet installed forced air heating appliances:
• The return air opening into the closet shall not be less
than specifi ed in the appliance’s listing.
• The cross-sectional area of the return duct system
leading into the closet, when located in the fl oor or
ceiling shall not be less than 235 in
2
(or 390 in
2
for 5
ton ready M1/M5 Furnaces).
CAUTION:
HAZARD OF ASPHYXIATION: Do not cover or
restrict return air opening.
• Means shall be provided that prevent inadvertent closure
of fl at objects placed over the return air opening located
in the fl oor of the closet (versus the vertical front or side
wall).
• The total free area of openings in the fl oor or ceiling
registers serving the return air duct system must be at
least 235 in
2
. At least one register should be located
where it is not likely to be covered by carpeting, boxes
and other objects.
• Materials located in the return duct system must have a
fl ame spread classifi cation of 200 or less. This includes
a closet door if the furnace is in a closet.
• Noncombustible pans having 1” upturned fl anges are
located beneath openings in a fl oor duct system.
• Wiring materials located in the return duct system shall
conform to Articles 300-22 of the National Electrical
Code (ANSI C1/NFPA-70).
• Gas piping is not run in or through the return duct system.
CAUTION:
HAZARD OF ASPHYXIATION: Negative pressure
inside the closet, with closet door closed and
the furnace blower operating on high speed,
shall be no more negative than minus 0.05 inch
water column.
• Test the negative pressure in the closet with the air-
circulating fan operating at high speed and the closet
closed. The negative pressure is to be no more negative
than minus 0.05 inch water column.
• Air conditioning systems may require more duct register
and open louver area to obtain necessary airfl ow. Use
NORDYNE’s certiduct program to determine proper
duct sizes for air conditioning.
Supply Air Connections
For proper air distribution, the supply duct system must be
designed so that the static pressure measured external
to the furnace does not exceed the listed static pressure
rating shown on the furnace rating plate.
Location, size, and number of registers should be selected
on the basis of best air distribution and fl oor plan of the
home.
The supply air must be delivered to the heated
space by duct(s) secured to the furnace casing,
running full size and without interruption.
Three typical
distribution systems are shown in Figure 5
Figure 5. Typical Supply Duct System
A Single trunk duct
B
Dual trunk duct
w/crossover connector
C
Transition duct
w/branches
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