1.
Position the furnace to minimize ductwork length and fi ttings.
2.
Cut open a return air inlet. Th
e choices are furnace bottom,
either side, or any combination thereof (i.e., two sides or a side
and the bottom).
!
WARNING
DO NOT USE THE REAR PANEL AS A RETURN AIR
INLET. Th
ere is insuffi
cient room to permit adequate
airfl ow.
In all cases, cut the inlet air opening the full width of the knockouts.
3.
Connect the return air duct or fi lter fi tting to the furnace. Th
e
connection should be sealed air tight to prevent entraining
combustion gases from an adjacent fuel burning appliance,
or entraining combustion air for this furnace or adjacent fuel
burning appliances.
4.
Ensure that there is adequate space and accessibility for air fi lter
removal.
NOTICE
NOTE: If two return air inlets are used, both must be
equipped with fi lters.
5.
If an air conditioning evaporator coil is required, position it on
the supply air side of the furnace. Ensure that no air can bypass
the evaporator coil.
6.
Connect the supply air plenum to the supply air outlet.
Flexible duct connectors
are an eff ective device to prevent the tele-
graphing of mechanical noise from the furnace to other parts of the
home via the ductwork. If using fl exible connectors, ensure that the
adjoining duct is independently supported.
Defi nitions
!
WARNING
Never allow the products of combustion from the fl ue to
enter the return air or supply air ductwork.
All return air ductwork must be adequately sealed and
secured to the furnace with sheet metal screws. Tape the
sheet metal seams in the vicinity of the furnace with duct
tape or similar material.
When the furnace is mounted on a platform with return
air through the bottom, it must be sealed air tight between
the furnace and the return air plenum. Th
e fl oor or plat-
form must provide sound physical support of the furnace
without sagging, cracks or gaps around the base, providing
a seal between the support and the base.
Models capable of 5 tons of airfl ow for air conditioning must have
dual return air inlets for optimal airfl ow and air fi ltration. If not
specifi cally stated by the fi lter manufacturer, for eff ective air fi ltration
assume a maximum velocity of 300 FPM for disposable type fi lters or
600 FPM for permanent type air fi lters.
GUIDE: Filter free area (in
2
) = 144 x (CFM / desired velocity (FPM))
NOTICE
IMPORTANT: Some high effi
ciency fi lters have a greater
than normal resistance to airfl ow. Th
is can adversely aff ect
furnace operation.
Ductwork Steps
7 - DUCTWORK
8 - VENTILATION AND COMBUSTION AIR
“
Vent and Chimney
” refer to open passageways that convey vent gas-
ses from the furnace, or its vent connector to the outside. Vents can
be horizontal or vertical. When they serve only one gas appliance,
they are called “dedicated” vents or chimneys. When they serve mul-
tiple gas appliances, they are called “common” vents or chimneys.
“
Vent Connector
” refers to a pipe or duct that connects the furnace
!
WARNING
READ, UNDERSTAND AND FOLLOW ALL INSTRUC-
TIONS IN THIS SECTION. FAILURE TO PROPERLY
VENT OR SUPPLY COMBUSTION AIR TO THIS FUR-
NACE CAN CAUSE CARBON MONOXIDE POISON-
ING, OR AN EXPLOSION OR FIRE, RESULTING IN
PROPERTY DAMAGE, PERSONAL INJURY OR LOSS
OF LIFE.
to a vent or chimney. Vent connectors usually run from the furnaces
vent collar to the vent or chimney. Vent connectors may have vertical
and horizontal runs.
“
Venting System”
refers to a continuous open passageway from
the vent collar to the outside. Venting systems usually have a vent
connector(s) and a vent or chimney. Venting systems commonly
serve a single furnace, or a single furnace and a hot water heater.
Other multiple appliance venting systems are less common.
“
Fan Assisted Combustion System
” refers to an appliance equipped
with an integral mechanical means to either draw or force products
of combustion through the combustion chamber and/or heat ex-
changer. Th
is series furnace uses a draft inducer to draw combustion
products through the heat exchanger and is considered to have a fan-
assisted combustion system. Category IV furnaces with fan-assisted
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