O137 15
CIRCULATING AIR FILTERS
One of the most common cause of a problem in a forced air heating system is a blocked or dirty
filter. Circulating air filters must be inspected monthly for dirt accumulation and replaced if neces-
sary. Failure to maintain clean filters can cause premature heat exchanger failure.
A new home may require more frequent replacement until all construction dust and dirt is re-
moved. Circulating air filters are to be installed in the return air duct external to the furnace cabi-
net.
CAUTION
Before performing any service on this furnace, including checking or replacing circulating air filters
- disconnect the main power supply.
DO NOT operate the furnace without circulating air filters in place.
MINIMUM FILTER SIZES
FURNACE INPUT FILTER SIZE TYPE
45M 188 IN
2
PERMANENT
75M 287 IN
2
PERMANENT
100M 303 IN
2
PERMANENT
125M 347 IN
2
PERMANENT
150M 625 IN
2
PERMANENT
45M 375 IN
2
DISPOSABLE
75M 555 IN
2
DISPOSABLE
100M 606 IN
2
DISPOSABLE
125M 694 IN
2
DISPOSABLE
150M 1250 IN
2
DISPOSABLE
PERMANENT NOMINAL 600 C.F.M. DISPOSABLE NOMINAL 300 C.F.M.
TEMPERATURE RISE
The temperature difference between the supply air and the return air of the furnace is known as
the temperature rise. This furnace is designed to operate within the temperature rise range dis-
played on the furnace series and rating plate. To ensure satisfactory performance, the tempera-
ture rise of the furnace must be measured and if necessary adjusted. Use the following procedure
to measure and adjust the temperature rise:
• Before starting the furnace visually inspect all joints and seams in the supply and return air
ducts for leaks. Repair them if necessary.
• Adjust the room thermostat to obtain constant operation.
• Allow the furnace to operate for at least fifteen (15) minutes.
• With an accurate thermometer measure the temperature at the return air. If a combination in-
door / outdoor system is used, the temperature must be measured downstream of the connec-
tion.
• Measure the outlet air tempreture at a point approximately twelve to eighteen (12 -18) inches
from the furnace in the supply air duct work. It may be necessary to measure the outlet air at
several places to obtain an accurate average. NOTE: IF AN AIR CONDITIONING COIL IS
INSTALLED, TAKE CARE SO AS NOT TO DAMAGE THAT COIL.
• Adjust the temperature by changing circulating air blower speed tap. Increasing the motor
speed lowers the temperature rise while lowering the motor speed increases the temperature
rise.
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