21
5. Turn ON gas and relight appliances turned off in step
1. Ensure all the appliances are functioning properly
and that all pilot burners are operating.
Temperature Rise
Air temperature rise is the temperature difference between
supply and return air. The proper amount of temperature rise
is usually obtained when the unit is operated at the rated input
with the “as shipped” blower speed. If the correct amount
of temperature rise is not obtained, it may be necessary to
change the blower speed.
An incorrect temperature rise can cause condensing in or
overheating of the heat exchanger. Determine and adjust the
temperature rise as follows. The temperature rise must be
within the range specified on the rating plate or Specification
Sheet applicable to your model.
(Please contact your dis
-
tributor or our website for the applicable Specification Sheet
referred to in this manual.)
SUPPLY
AIR
RETURN
AIR
Temperature Rise Measurement
1. Operate furnace with burners firing approximately
15 minutes. Ensure all registers are open and all
duct dampers are in their final (fully or partially open)
position.
2. Place thermometers in the return and supply ducts as
close to the furnace as possible. Thermometers must
not be influenced by radiant heat by being able to “see”
the heat exchanger.
3. Subtract the return air temperature from the supply
air temperature to determine the air temperature rise.
Allow adequate time for thermometer readings to
stabilize.
4. Adjust temperature rise by adjusting the circulator
blower speed. Increase blower speed to reduce
temperature rise. Decrease blower speed to increase
temperature rise. Refer to the following section for
speed changing details.
6. Turn ON power and close thermostat “R” and “W”
contacts to provide a call for heat.
7. Using a leak detection solution or soap suds to check
for leaks at outlet pressure tap. Bubbles forming indicate
a leak. SHUT OFF GAS AND REPAIR ALL LEAKS
IMMEDIATELY!
8. Measure the gas manifold pressure with burners firing.
Adjust manifold pressure using the
Manifold Gas
Pressure
table shown below.
Natural Gas
3.2" - 3.8" w.c.
Propane Gas
9.7" - 10.3" w.c.
Manifold Gas Pressure
9. Remove regulator cover screw from the outlet pressure
regulator and turn screw clockwise to increase pressure
or counterclockwise to decrease pressure. Replace
regulator cover screw.
10. Turn OFF all electrical power and gas supply to the
system.
11. Remove the manometer hose from the hose barb fitting
or outlet pressure tap .
12. Replace outlet pressure tap:
White-Rodgers valve: Turn outlet pressure test screw
in to seal pressure port (clockwise, 7 in-lb minimum).
13. Turn ON electrical power and gas supply to the system.
14. Close thermostat contacts to provide a call for heat.
15. Retest for leaks. If bubbles form, SHUT OFF GAS AND
REPAIR ALL LEAKS IMMEDIATELY!
Gas Input Rate Measurement (Natural Gas Only)
The gas input rate to the furnace must never be greater than
that specified on the unit rating plate. To measure natural
gas input using the gas meter, use the following procedure.
1. Turn OFF the gas supply to all other gas-burning
appliances except the furnace.
2. While the furnace is operating, time and record one
complete revolution of the smallest gas meter dial.
3. Calculate the number of seconds per cubic foot (sec/
ft
3
) of gas being delivered to the furnace. If the dial
is a two cubic foot dial, divide the number of seconds
recorded in step 2 by two.
4. Calculate the furnace input in BTUs per hour (BTU/
hr). Input equals the installation’s gas heating value
multiplied by a conversion factor (hours to seconds),
divided by the number of seconds per cubic foot. The
measured input must not be greater than the input
indicated on the unit rating plate.
EXAMPLE:
Installation’s gas heating (HTG) value: 1,000 BTU/ft
3
(Obtained from gas supplier)
Installation’s seconds per cubic foot: 34 sec/ ft
3
Conversion Factor (hours to seconds): 3600 sec/hr
Input = (Htg. value x 3600) ק seconds per cubic foot
Input = (1,000 BTU/ft
3
x 3600 sec/hr) ק 34 sec/ ft
3
Input = 106,000 BTU/hr
This measured input must not be greater than the input
indicated on the unit rating plate.