Service Manual

12
SYSTEM OPERATION
hydrochloric acid
cements and glues
antistatic fabric softeners for clothes dryers
and masonry acid washing materials
• Isolate a non-direct vent furnace if it is installed near
an area frequently contaminated by any of the above
substances. This protects the non-direct vent furnace
from airborne contaminants. To ensure that the en-
closed non-direct vent furnace has an adequate sup-
ply of combustion air, vent from a nearby uncontami-
nated room or from outdoors. Refer to the Combus-
tion and Ventilation Air Requirements section in this
manual or the installation instructions for details.
• If the furnace is used in connection with a cooling
unit, install the furnace upstream or in parallel with
the cooling unit coil. Premature heat exchanger fail-
ure will result if the cooling unit coil is placed in the
return air of the furnace.
• If the furnace is installed in a residential garage, po-
sition the furnace so that the burners and ignition
source are located not less than 18 inches (457 mm)
above the floor. Protect the furnace from physical dam-
age by vehicles.
• If the furnace is installed horizontally, the furnace ac-
cess doors must be vertical so that the burners fire
horizontally into the heat exchanger. Do not install
the unit with the access doors on the “up/top” or “down/
bottom” side of the furnace.
• On counterflow installations, the air conditioning coil
must be downstream on the supply (positive) side of
the furnace heat exchanger.
• Counterflow Installation over a noncombustible floor.
Before setting the furnace over the plenum opening,
ensure the surface around the opening is smooth and
level. A tight seal should be made between the fur-
nace base and floor by using a silicone rubber caulk-
ing compound or cement grout.
• Counterflow Installation over a combustible floor. If
installation over a combustible floor becomes neces-
sary, use an accessory sub-base (see Specification
Sheet applicable for your model for details). A spe-
cial accessory sub-base must be used for upright
counterflow unit installations over any combustible
material including wood. Refer to sub-base instruc-
tions for installation details. Follow the instructions
with the sub-base for proper installation. Do not in-
stall the furnace directly on carpeting, tile, or other
combustible material other than wood flooring.
(NOTE: The sub-base will not be required if an air
conditioning coil is installed between the supply air
opening on the furnace and the floor.)
POSITION* SIDES REAR FRONT BOTTOM FLUE TOP
Upflo w 0" 0" 1" C 0" 1"
Hor izo nt al 6" 0" 1" C 0" 6"
*MEC96 MINIMUM CLEARANCES TO COMBUSTIBLE MATERIALS
POSITION* SIDES REAR FRONT BOTTOM FLUE TOP
Counterflow0"0"1"NC0"
Hor izont al 6" 0" 1" C 0" 6"
*CEC96 MINIMUM CLEARANCES TO COMBUSTIBLE MATERIALS
• C = If placed on combustible floor, floor MUST be wood only.
• NC = For installation on non-combustible floors only. A combustible
subbase must be used for installations on combustible flooring.
• For servicing or cleaning, a 24" front clearance is recommended.
• Unit connections (electrical, flue, and drain) may necessitate greater
clearances than the minimum clearances listed above.
• In all cases, accessibility clearance must take precedence over from
the enclosure where accessibility clearances are greater.
• Approved for line contact in the horizontal position.
Clearances and Accessibility
Installations must adhere to the clearances to combustible
materials to which this furnace has been design certified.
The minimum clearance information for this furnace is pro-
vided on the unit’s clearance label. These clearances must
be permanently maintained. Refer to Specification Sheet for
minimum clearances to combustible materials. Clearances
must also accommodate an installation’s gas, electrical,
and drain trap and drain line connections. If the alternate
combustion air intake or vent/flue connections are used on
a 90% furnace, additional clearances must be provided to
accommodate these connections. Refer to Vent Flue Pipe
and Combustion Air Pipe section in this manual or the in-
stallation instructions for details. NOTE: In addition to the
required clearances to combustible materials, a minimum
of 24 inches service clearance must be available in front of
the unit.
A furnace installed in a confined space (i.e., a closet or
utility room) must have two ventilation openings with a total
minimum free area of 0.25 square inches per 1,000 BTU/hr
of furnace input rating. One of the ventilation openings must
be within 12 inches of the top; the other opening must be
within 12 inches of the bottom of the confined space. In a
typical construction, the clearance between the door and
door frame is usually adequate to satisfy this ventilation
requirement.