Rheem GLH series, Installation Instructions Manual

Page: 26 / 36

26
FIGURE 23
TYPICAL FURNACE NAME PLATE
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.
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 22.
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 23.
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.
Ideally the measured temperature rise
should be in the middle of the range.
IMPORTANT: Some high-efficiency
filters have a greater than normal
resistance to airflow. This can
adversely affect furnace operation. BE
SURE TO CHECK AIRFLOW if using
any filter other than factory-provided
filter.
FIGURE 22
TEMPERATURE RISE MEASUREMENT
AIR FLOW