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Downflow Application Installation Clearances
Top
Bottom
Left Side
Right Side
Type of Vent
Connector
Type C Type B1
Top 1 in. (25 mm) 1 in. (25 mm)
*Front 3 in. (76 mm) 3 in. (76 mm)
Back 0 0
Sides 0† 0
Vent 6 in. (152 mm) 1 in. (25 mm)
Floor NC†† NC††
*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
†Left side requires 3 in. if a single wall vent is used on 14 −1/2 in. cab-
inets, or 2 in. if a single wall vent is used on 17 − 1/2 in. cabinets.
††The furnace may be installed on a combustible wood floor if an
optional additive base is installed between the furnace and the
combustible floor.
FIGURE 9
WARNING
Improper installation of the furnace can result in per-
sonal injury or death. Combustion and flue products
must never be allowed to enter the return air system
or the living space. Use screws and joint tape to seal
the return air system to the furnace.
In platform installations with bottom return air, the
furnace should be sealed airtight to the return air ple-
num. A door must never be used as a portion of the
return air duct system. The base must provide a
stable support and an airtight seal to the furnace. Al-
low absolutely no sagging, cracks, gaps, etc.
The return and supply air duct systems must never
be connected to or from other heating devices such
as a fireplace or stove, etc. Fire, explosion, carbon
monoxide poisoning, personal injury and/or proper-
ty damage could result.
WARNING
The blower access panel must be securely in place
when the blower and burners are operating. Gas
fumes, which could contain carbon monoxide, can
be drawn into living space resulting in personal inju-
ry or death.
Filters
This unit is not equipped with a filter or rack. A field−pro-
vided high−velocity filter is required for the unit to operate
properly. Table 3 lists the recommended minimum filter
sizes.
A filter must be in place any time the unit is operating.
TABLE 3
Furnace
Cabinet Size
Return Air Filter Size (inches)
14−1/2" 14 X 25 X 1 (1)
17−1/2" 16 X 25 X 1 (1)
21" 20 X 25 X 1 (1)
24−1/2" 24 X 25 X 1 (1)
Duct System
Use industry-approved standards to size and install the
supply and return air duct system. This will result in a quiet
and low-static system that has uniform air distribution.
Ensure that you have made a seal between the supply air
plenum and the furnace and between the furnace and the
return air plenum.
NOTE − Do not operate the furnace with an external static
pressure that exceeds 0.5 inches w.c. Higher external stat-
ic pressures may cause erratic limit operation.
Return Air Plenum
NOTE − Return air must not be drawn from a room
where this furnace, or any other gas−fueled ap-
pliance (i.e., water heater), or carbon monoxide−
producing device (i.e., wood fireplace) is installed.
When return air is drawn from a room, a negative pres-
sure is created in the room. If a gas appliance is operating
in a room with negative pressure, the flue products can
be pulled back down the vent pipe and into the room. This
reverse flow of the flue gas may result in incomplete com-
bustion and the formation of carbon monoxide gas. This
toxic gas might then be distributed throughout the house
by the furnace duct system.
Venting
A 4−inch diameter flue transition is factory-installed on all
models. Modifying or removing the flue transition will
cause the unit to operate unsafely and will void the unit
certification. The vent connector does not require insula-
tion.
The G40DF(X) series units are classified as fan−assisted
Category I furnaces when vertically vented according to
the latest edition of National Fuel Gas Code (ANSI
Z223.1/NFPA 54) in the USA and the current standards of
CSA B149 Natural Gas and Propane Installation Code in
Canada. A fan−assisted Category I furnace is an appliance
equipped with an integral mechanical means to either draw
or force combustion products through the combustion
chamber and/or heat exchanger.
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