650.75-N4U
035-14370-000
10
Unitary Products Group
NOTE:Some accessories such as electronic air cleaners and
pleated media may require a larger side opening.
The return duct may be attached to the furnace by S-cleat,
bend tabs or other approved methods. Be sure to seal the
duct to the furnace to prevent air leakage.
Those applications over 1800 CFM require either return from
two sides, one side and the bottom, or bottom only. For bot-
tom only application, see data and notes on blower perfor-
mance data tables in this manual.
Where the return duct system is not complete, the return con-
nection must run full size to a location outside the utility room
or basement. For further details, consult Section 5.3 (Air for
Combustion and Ventilation) of the National Fuel Gas Code,
ANSI Z223.1, or CAN/CGA B149.1 or.2, Installation Code -
latest editions.
Bottom Return
Bottom return applications normally pull return air through a
base platform or return air plenum. Be sure the return plat-
form structure is suitable to support the weight of the furnace.
Be sure to seal the furnace to plenum connection to prevent
air leakage. (Refer to Figure 3 on page 9) and (Refer to
Table 1 on page 6).
The bottom panel is equipped with a perforated opening for
easy removal. Tabs must be cut with sheet metal snips to
allow removing knock-out. Scribe marks are included for
forming flanges for attachment of the return air ductwork.
NOTE:If an external mounted filter rack is being used, see
the instructions provided with that accessory for proper hole
cut size.
Upflow attic installations must meet all minimum clearances
to combustibles and have floor support with required service
accessibility.
DOWNFLOW/HORIZONTAL MODELS-
DOWNFLOW APPLICATION
DOWNFLOW FILTERS
A top return filter rack is supplied with
the furnace. Two 14" x 20" permanent
washable filters are supplied with each
unit.
Downflow furnaces typically are
installed with the filters located above
the furnace, extending into the return
air duct.
Any branch duct must attach to the ver-
tical ductwork above the filter height
(FH) and for proper installation refer to
Figure 6.
The filter rack (provided) should be secured to the center of
the front and rear flanges at the furnace top. Drill a hole
through the front and rear duct flange into the filter rack and
secure it with a sheet metal screw.
Refer to the unit rating plate for furnace model then see the
dimensions page of this instruction for return air plenum
dimensions. Install the plenum following instructions under
Ductwork in this instruction.
All installations must have a filter installed.
FIGURE 6 : DOWNFLOW FILTERS
N O T E : F I L T E R A C C E S S T H R U D U C T -
W O R K M U S T B E P R O V I D E D F O R
R E M O V A L A N D C L E A N I N G
B R A N C H
D U C T S
C R O S S S E C T I O N A - A
( W I T H P L E N U M A N D F I L T E R S )
D U C T W O R K
F I L T E R S
F I L T E R
R A C K
F H
R A C K A N D F I L T E R S S E C U R E D
I N S I D E B L O W E R S E C T I O N
F O R S H I P M E N T
F I L T E R R A C K
( F A C T O R Y S U P P L I E D )
C A S I N G S I Z E D I M E N S I O N F H
1 4 - 1 / 2 " 1 3 - 1 / 4 "
1 7 - 1 / 2 " 1 2 - 1 / 2 "
2 1 " 1 1 - 1 / 2 "
2 4 - 1 / 2 " 9 - 3 / 4 "
A
A
