66
Rev. 0
SERVICING
S-15 CHECKING DUCT STATIC
The maximum and minimum allowable external static pres-
sures are found in the specification section. These tables
also show the amount of air being delivered at a given static
by a given motor speed or pulley adjustment.
The furnace motor cannot deliver proper air quantities
(CFM) against statics other than those listed.
Too great of an external static pressure will result in insuf-
ficient air that can cause excessive temperature rise, re-
sulting in limit tripping, etc. Whereas not enough static may
result in motor overloading.
To determine proper air movement, proceed as follows:
1. With clean filters in the furnace, use a draft gauge (in-
clined manometer) to measure the static pressure of
the return duct at the inlet of the furnace. (Negative Pres-
sure)
2. Measure the static pressure of the supply duct. (Posi-
tive Pressure)
3. Add the two (2) readings together for total external static
pressure.
NOTE: Both readings may be taken simultaneously and
read directly on the manometer if so desired. If an air con-
ditioning coil or Electronic Air Cleaner is used in conjunc-
tion with the furnace, the readings must also include these
components. Refer to the following figure.
4. Consult proper airflow tables in
BLOWER PERFOR-
MANCE SPECIFICAIONS section of this manual or
Specifications Sheet for the quantity of air.
If the total external static pressure exceeds the minimum
or maximum allowable statics, check for closed dampers,
registers, undersized and/or oversized poorly laid out duct
work.
CONDENSATE
DRAIN TRAP
w/ 3/4" PVC
DISCHARGE
(RIGHT OR
LEFT SIDE)
A m a n a
Electron ic A ir Cleaner
C a u tio n
Hi gh Vol tag e
To av oi d pe rson al in ju ry,
wa it 15
se co nds a fte r d e-e ne rg i zin g u ni t
b efore t o uch in g un it i nteri or.
CUTAWAY OF DUCTWORK
TO EXPOSE COIL
RETURN
AIR
SUPPLY
AIR
INCLINED
MANOMETER
Checking Static Pressure
S-16 CHECKING TEMPERATURE RISE
The more air (CFM) being delivered through a given fur-
nace, the less the rise will be; so the less air (CFM) being
delivered, the greater the rise. The temperature rise should
be adjusted in accordance to a given furnace specifica-
tions and its external static pressure. An incorrect tempera-
ture rise may result in condensing in or overheating of the
heat exchanger. An airflow and temperature rise table is
provided in the blower performance specification section.
Determine and adjust temperature rise as follows:
1. Operate furnace with burners firing for approximately
ten minutes. Check BTU input to furnace - do not ex-
ceed input rating stamped on rating plate. Ensure all
registers are open and all duct dampers are in their fi-
nal (fully or partially open) position.
2. Place thermometers in the return and supply ducts as
close to the furnace as possible. Thermometers must
not be influenced by radiant heat by being able to “see”
the heat exchanger.
RISE =
T
SUPPLY -
T
RETURN
T
SUPPLY
T
RETURN
SUPPLY
AIR
RETURN
AIR
HEAT EXCHANGER
RADIATION "LINE OF SIGHT"
Checking Temperature Rise
3. Subtract the return air temperature from the supply air
temperature to determine the air temperature rise. Al-
low adequate time for thermometer readings to stabi-
lize.
4. Adjust temperature rise by adjusting the circulator blower
speed. Increase blower speed to reduce temperature
rise. Decrease blower speed to increase temperature
rise. Refer to
Circulator Blower Speed section in the
PRODUCT DESIGN section of this manual for speed
changing details. Temperature rise is related to the
BTUH output of the furnace and the amount of air (CFM)
circulated over the heat exchanger. Take motor am-
perage draw to determine that the motor is not over-
loaded during adjustments.
