Circulating Air Requirements; Plenums & Air Ducts; Return Air Connections; Upflow & Horizontal Furnaces - Oxbox J951X U Series Installation Instructions Manual

For Installations where there is limited clearance for the
J-Trap (such as an attic where it may be installed between
ceiling joists), either side of the J-Trap can be shortened to
a minimum of 3 Inches. See

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 confined spaces, all return ductwork must be
adequately sealed. When return air is provided
through the bottom of the furnace, 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 floor 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 fire, explosion, carbon monoxide
poisoning, personal injury, or property damage.
Plenums & Air Ducts
• 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).
• On upflow furnaces, if the maximum airflow is 1,600 CFM
or more, two openings shall be used for return air to
comply with government mandated efficiency standards.
Downflow furnaces can only use one return opening.
• It is recommended that the outlet duct contain a removable
access panel. The opening should be accessible when
the furnace is installed in service and shall be of a size
that smoke or reflected light may be observed inside
the casing to indicate the presence of leaks in the heat
exchanger. The cover for the opening shall be attached
in a way that prevent leaks.
• If outside air is used as return air to the furnace for
ventilation or to improve indoor air quality, the system
must be designed so that the return air is not less than
60° F (15° C) during operation. If a combination of indoor
and outdoor air is used, the ducts and damper system
must be designed so that the return air supply to the
furnace is equal to the return air supply under normal,
indoor return air applications.
.
Figure 11 (page 15)
• When a cooling system is installed which uses the
furnace blower to provide airflow over the indoor coil, the
coil must be installed downstream (on the outlet side) of
the furnace or in parallel with the furnace.
• If a cooling system is installed in parallel with the
furnace, a damper must be installed to prevent chilled
air from entering the furnace and condensing on the heat
exchanger. If a manually operated damper is installed,
it must be designed so that operation of the furnace is
prevented when the damper is in the cooling position and
operation of the cooling system is prevented when the
damper is in the heating position.
• Seal all connections and joints with industrial grade
sealing tape or liquid sealant. Requirements for sealing
ductwork vary from region to region. Consult with local
codes for requirements specific to your area.

Return Air Connections

• In applications where the supply ducts carry heated air to
areas outside the space where the furnace is installed,
the return air must be delivered to the furnace by duct(s)
secured to the furnace casing, running full size and
without interruption. Do not use the back of the furnace
for return air.
• Position the furnace with the return air ductwork ensuring
even alignment of furnace (or coil casing) air opening
and return air duct. NOTE: The ductwork must have an
opening equal to that of the return air opening of the
furnace (or coil casing). See
for return air opening size.
Figure 30 (page 29)
Upflow & Horizontal Furnaces
• The return air ductwork may be connected to the left side,
right side, or bottom of the furnace. NOTE: If using the left
or right side of the furnace for return air, the bottom panel
(Figure 32) must not be removed from the bottom of the
furnace.
WARNING:
The bottom panel of the furnace must be in place
when the furnace is installed with side return air
ducts. Removal of all or part of the base could
cause circulation of combustible products into
the living space and create potentially hazardous
conditions, including carbon monoxide poisoning
that could result in personal injury or death.
• Side Return Installations: To attach the return air duct
to the left or right side of the furnace, punch out the 4
knockouts from the side of the furnace (
Using sharp metal cutters, cut an opening between all 4
knockouts to expose the blower assembly. Position the
return air duct over the opening and secure to the side
with sheet metal screws.
• Bottom Return Installations: If using the bottom of the
furnace for return air, the bottom panel (
be removed from the bottom of the furnace. See
for removal instructions. Position the furnace over
19
the return air duct and secure together with sheet metal
screws. Make sure the screws penetrate the duct and
furnace casing.
or
Figure 29 (page 29)
).
Figure 30
) must
Figure 30
page
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