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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 poisoning 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
fireplace 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
square inches (or 390 square inches 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 sq. in. 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 ob-
tain necessary airflow. Use NORDYNE’s
certiduct program to determine proper duct
size for A/C.
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.