Air Flow - Rheem GF902U Series Installation Instructions Manual

AIR FLOW

The importance of proper air flow over the
heat exchanger cannot be over
emphasized.
CAUTION
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 EQUIPMENT
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 49.
2. Insert a thermometer in the return air
duct as close to the furnace as
possible.
3. Operate the furnace. High fire and
low fire heating modes have the
same temperature rise range.
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 50.
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.
WARNING
THE MEASURED TEMPERATURE
RISE SHOULD BE AS CLOSE TO THE
MIDDLE OF THE STATED RANGE AS
POSSIBLE. FOR EXAMPLE, IF THE
54
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 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.
FIGURE 50
TYPICAL FURNACE NAME PLATE
FIGURE 49
TEMPERATURE RISE MEASUREMENT