33
FIGURE 28
FURNACE NAME PLATE
AIR FLOW
The importance of proper air flow over
the heat exchanger cannot be over
emphasized. One of the most common
causes of heat exchanger failure is
overheating due to low air flow. An air
flow table is located inside the blower
door and on the following pages.
NOTE: The installation of the duct
system is under the control of the
installing contractor. If the duct system
is not correctly sized and installed, the
homeowner may experience air noise,
low or no airflow out of some vents,
component failures, or high utility bills.
Other miscellaneous problems are also
possible.
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 27.
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 28.
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 dip switches on the blower
interface board to adjust airflow.
Ideally the measured temperature rise
should be in the middle of the range.
The rise range is the same for high and
low inputs.
FIGURE 27
TEMPERATURE RISE MEASUREMENT
To Next Page
Loading...
