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Filter Arrangement
FIRE,
CARBON
MONOXIDE
AND POISONING
HAZARD
Failure
to follow
this warning
could
result in fire, personal
iniury or death.
Never
operate
a furnace
without
a filter or filtration
device
installed.
Never
operate
a furnace
with
filter
or filtration
device
access doors removed.
Provide
duct transitions,
as required,
to smoothly
transition
airflow
from
the return
duct system
to the filter
(or IAQ
device)
to the
furnace
when
the dimensions
of the ductwork
or furnace
return air
opening
do not match the required
filter or IAQ device dimensions.
See the instructions
supplied
with factory-accessory
duct adapters.
There are no provisions
for an internal
filter rack in these furnaces.
An external
filter is required
and is purchased
separately.
A field
supplied
accessory
air cleaner may also be used in place of the filter
rack.
For upflow
applications,
the filter can be installed
on either side of
the furnace,
the bottom
of the furnace
or any combination
of side
and bottom
of the furnace.
See Fig. 18, 19 and 25.
For
downflow
applications,
the
filter
rack
(or
field
supplied
accessory
air
cleaner)
must
only
be connected
to the
bottom
opening
on the furnace.
See Fig. 19 and 26.
For
horizontal
applications,
the
filter
rack
(or
field
supplied
accessory
air cleaner)
can be connected
to the bottom
opening
on
the furnace.
For side return use in the horizontal
position,
refer to
Fig. 27. If both side and bottom
openings
are used in Fig. 27, each
opening
used will require
a filter.
A filter rack or any field supplied
accessory
air cleaner can also be
installed
in the common
return duct prior to entering
the return air
opening
in any orientation.
Refer to the instructions
supplied
with filter rack
or accessory
air
filter for additional
assembly
and installation
options.
See Table 7 for filter size details.
Filter and Return Duct Sizing
Pressure drop must be taken into account when
sizing filters, filter
racks,
IAQ devices,
and associated
system
ductwork.
See Table 5
for
a comparison
of Pressure
Drop
(initial/clean
resistance
to
airflow) versus Airflow
for a variety of filter media types and sizes.
These are representative
numbers.
Consult
the filter or IAQ device
manufacturers'
specification
sheet
for
performance
data
for
a
particular
filter media or IAQ device.
Design
the filter
and associated
ductwork
for the best match
of
pressure
drop versus filter size. Best practice
usually
chooses
filter
systems
with
pressure
drops
under
0.2 in. W.C. (50 Pa), with the
best blower
electrical
efficiency
and system
airflow
performance
occurring
with filter pressure
drops
under 0.1 in. W.C. (25 Pa).
Due to the relatively
high pressure
drops
of 1-in.
(25 mm) thick
after-market
filter
media,
it is recommended
that the filtration
system be designed
for at least 2-in.
(51 mm) thick media.
TIPS
FROM
CONTRACTORS:
Install
a media cabinet
capable
of incorporating
a 4-in.
(102 mm) thick media filter. This allows
room for future upgrades
to other IAQ devices.
Design
the duct
system
FIRST
to determine
how
much
pressure
drop may be allowed
in the filter system.
See the Air
Ducts
section.
Excessive
filter
pressure
drop
often
compromises
system
airflow
and
duct
performance,
causes
inadequate
airflow
to the furthest
ends of the duct system,
as
well
as causes
excess
noise
and
higher
than
anticipated
electrical
consumption.
21
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