1.
Position the furnace to minimize ductwork length and ttings.
2.
Cut open a return air inlet. 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. ere is insu cient room to permit adequate
air ow.
In all cases, cut the inlet air opening the full width of the knockouts.
3.
Connect the return air duct or lter tting to the furnace. 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 lter
removal.
NOTICE
NOTE: If two return air inlets are used, both must be
equipped with 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 e ective device to prevent the tele-
graphing of mechanical noise from the furnace to other parts of the
home via the ductwork. If using exible connectors, ensure that the
adjoining duct is independently supported.
De nitions
!
WARNING
Never allow the products of combustion from the 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. e 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 air ow for air conditioning must have
dual return air inlets for optimal air ow and air ltration. If not
speci cally stated by the lter manufacturer, for e ective air ltration
assume a maximum velocity of 300 FPM for disposable type lters or
600 FPM for permanent type air lters.
GUIDE: Filter free area (in
2
) = 144 x (CFM / desired velocity (FPM))
NOTICE
IMPORTANT: Some high e ciency lters have a greater
than normal resistance to air ow. is can adversely a 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 Connec tor” 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. is series furnace uses a dra 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
13
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