53
AIR FLOW
The importance of proper air flow over the
heat exchanger cannot be over
emphasized.
IT IS IMPORTANT THAT EACH DUCT
SYSTEM BE SIZED AND INSTALLED
FOR THE SPECIFIC APPLICATION BY
PROPERLY APPLYING THE
APPROPRIATE INDUSTRY ACCEPTED
STANDARD. IF LESS THAN MINIMUM
STANDARDS ARE APPLIED, THE
EQUIPMENT USER COULD EXPECT
TO EXPERIENCE HIGHER UTILITY
BILLS, MAJOR COMPONENT
FAILURE, VARYING DEGREES OF AIR
NOISE OR OTHER UNSATISFACTORY
ISSUES, OVER WHICH THE
MANUFACTURER HAS NO CONTROL.
TEMPERATURE RISE CHECK
To determine if the air flow is correct,
make a temperature rise check.
1. Insert a thermometer in the supply
air duct as close to the furnace as
possible yet out of a direct line from
the heat exchanger. See Figure 47.
2. Insert a thermometer in the return air
duct as close to the furnace as
possible.
3. Operate the furnace.
4. When the thermometer in the supply
air duct stops rising (approximately
five minutes), subtract the return air
temperature from the supply air
temperature. The difference is the
temperature rise.
5. Compare the measured temperature
rise to the approved temperature rise
range listed on the furnace name
plate. See Figure 48.
If the measured temperature rise is above
the approved range, the air flow is too
low. More air must be moved by speeding
up the blower, by removing restrictions in
the duct system, or by adding more
supply or return air duct. If the measured
temperature rise is below the approved
range, the air flow is too much. Use lower
speed tap on the multi-speed blower.
THE MEASURED TEMPERATURE
RISE SHOULD BE AS CLOSE TO THE
MIDDLE OF THE STATED RANGE AS
POSSIBLE. FOR EXAMPLE, IF THE
RISE RANGE IS 40 TO 70 DEGREES,
THE MOST IDEAL RISE WOULD BE 55
DEGREES (THE MIDDLE OF THE RISE
RANGE). IN ALL APPLICATIONS, THE
FIGURE 47
TEMPERATURE RISE MEASUREMENT
FIGURE 48
TYPICAL FURNACE NAME PLATE
!
WARNING
!
CAUTION
INSTALLER MUST ADJUST THE
TEMPERATURE RISE TO THIS
"MIDDLE" POINT AS CLOSELY AS
POSSIBLE. ALSO, THE
TEMPERATURE RISE SHOULD
NEVER BE ABOVE OR FALL
BELOW THE STATED RANGE.
DOING SO COULD CAUSE
DAMAGE TO THE HEAT
EXCHANGER OR INTERMITTENT
OPERATION WHICH COULD
CAUSE INJURY OR DEATH AND
WILL VOID THE
MANUFACTURER'S WARRANTY
FOR THIS PRODUCT.
