18
When the furnace is used in connection with a cooling unit,
the furnace should be installed in parallel with or on the
upstream side of the cooling unit to avoid condensa tion in
the heating element. With a parallel fl ow arrange ment, the
dampers or other means used to control the fl ow of air must
be adequate to prevent chilled air from entering the furnace
and, if manually operated, must be equipped with means to
prevent operation of either unit unless the damper is in the
full heat or cool position.
When the furnace is installed without a cooling coil, it is rec-
ommended that a removable access panel be provided in
the outlet air duct. This opening shall be accessible when the
furnace is installed and shall be of such a size that the heat
exchanger can be viewed for visual light inspection or such
that a sampling probe can be inserted into the airstream. The
access panel must be made to prevent air leaks when the
furnace is in operation.
When furnace duct(s) supply air outside the space containing
the furnace, a return air duct must terminate in the same space
as the supply duct and be sealed to the furnace casing.
When the furnace is heating, the temperature of the return
air entering the furnace must be between 55°F and 100°F.
C
HECKING
D
UCT
S
TATIC
Refer to your furnace rating plate for the maximum ESP (ex-
ternal duct static) rating.
Total external static refers to static pressure created by all
components external to the furnace cabinet. Cooling coils,
fi lters, ducts, grilles, registers must all be considered when
reading your total external static pressure. The supply duct
pressure must be read between the furnace and the cooling
coil. This reading is usually taken by removing the “A” shaped
block off plate from the end on the coil; drilling a test hole in it
and reinstalling the block off plate. Take a duct static reading
at the test hole. Tape up the test hole after your test is com-
plete. The negative pressure must be read between the fi lter
and the furnace blower.
Too much external static pressure will result in insuffi cient air
that can cause excessive temperature rise. This can cause
limit switch tripping and heat exchanger failure.
To determine total external duct static pressure, proceed as
follows;
1. With
clean
fi lters in the furnace, use a draft gauge (inclined
manometer) to measure the static pressure of the return
duct at the inlet of the furnace. (Negative Pressure)
2. Measure the static pressure of the supply duct. (Positive
Pressure)
3. The difference between the two numbers is .4” w.c.
Example:
static reading from return duct = -.1” w.c.
static reading from supply duct = .3” w.c.
total external static pressure on this system = .4” w.c.
NOTE:
Both readings may be taken simultaneously and read
directly on the manometer if so desired. If an air conditioner
coil or Electronic Air Cleaner is used in conjunction with the
furnace, the readings must also include these components,
as shown in the following drawing.
4. Consult proper tables for the quantity of air.
If the total external static pressure exceeds the maximum
listed on the furnace rating plate, check for closed dampers,
registers, undersized or poorly laid out duct work.
Digital
Manometer
Checking Static Pressure
Figure 10
F
ILTERS
- R
EAD
T
HIS
S
ECTION
B
EFORE
I
NSTALLING
T
HE
R
ETURN
A
IR
D
UCTWORK
Filters must be used with this furnace. Discuss fi lter mainte-
nance with the building owner. Filters do not ship with this
furnace, but must be provided by the installer. Filters must
comply with UL900 or CAN/ULCS111 standards.Damage or
repairs due to the installation of the furnace without fi lters is
not covered under the warranty.
U
PRIGHT
I
NSTALLATIONS
Depending on the installation and/or customer preference,
differing fi lter arrangements can be applied. Filters can be
installed in the central return register or a side panel external
fi lter rack kit (upfl ows), or the ductwork above a downfl ow
furnace. As an alternative, a media air fi lter or electronic air
cleaner can be used as the primary fi lter.
H
ORIZONTAL
I
NSTALLATIONS
Filters must be installed in either the central return register or
in the return air duct work.
