38
The typical value range for 1 cu. ft. of natural gas is around
1000 BTU. Check with your gas utility, if possible. In this
example, the furnace is consuming 78,000 BTUH.
NOTE: The final manifold pressure cannot vary by
more than ± 0.3” w.c. for Natural and + 0.5” for LP from
the specified setting. Consult your local gas supplier
if additional input rate adjustment is required.
4. Turn ON gas to and relight all other appliances
turned off in step 1. Be certain that all appliances
are functioning properly and that all pilot burners are
operating.
Temperature Rise
Temperature rise must be within the range specified on the
unit rating plate. An incorrect temperature rise may result
in condensing in or overheating of the heat exchanger.
An airflow and temperature rise table is provided in the
Specification Sheet applicable to your model. Determine
and adjust temperature rise as follows:
1.
Operate furnace with burners firing for approximately
ten 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 Startup
Procedure and Adjustment - Circulator Blower
Speeds for speed changing details.
SUPPLY
AIR
RETURN
AIR
Temperature Rise Measurement
Figure 50
8. Remove regulator cover screw from the outlet
pressure regulator adjust tower and turn screw
clockwise to increase pressure or counterclockwise
to decrease pressure. Replace regulator cover
screw.
9. Turn off all electrical power and gas supply to the
system.
10. Remove the manometer hose from the hose barb
fitting or outlet pressure tap.
11. Replace outlet pressure tap: White-Rodgers 36J22
valve: Turn outlet pressure test screw in to seal pressure
port (clockwise, 7 in-lb minimum).
12. Turn on electrical power and gas supply to the
system.
13. Close thermostat contacts “R” and “W” to energize the
valve.
Using a leak detection solution or soap suds, check for
leaks at outlet or screw (White-Rodgers valve). Bubbles
forming indicate a leak. SHUT OFF GAS AND REPAIR
ALL LEAKS IMMEDIATELY!
NOTE: For gas to gas conversion, consult your dealer
for appropriate conversion.
CAUTION
T
O
PREVENT
UNRELIABLE
OPERATION
OR
EQUIPMENT
DAMAGE
,
THE
INLET
GAS
SUPPLY
PRESSURE
MUST
BE
AS
SPECIFIED
ON
THE
UNIT
RATING
PLATE
WITH
ALL
OTHER
HOUSEHOLD
GAS
FIRED
APPLIANCES
OPERATING
.
Gas Input Rate Measurement (Natural Gas Only)
The actual 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 at high fire rate, time
and record one complete revolution of the gas meter
dial, measuring the smallest quantity, usually the dial
that indicates 1/2 cu. ft. per revolution. You will use
this number to calculate the quantity of gas in cubic
ft. if the furnace would consume if it ran steadily for
one hour (3600 seconds).
3. If the 1/2 cu. ft. dial was used, multiply your number
x 2.
EXAMPLE: If it took 23 seconds to complete one
revolution of the 1/2 ft. dial (23 x 2 = 46).
This tells us that at this rate, it would take 46 seconds to
consume one cu. ft. of gas. 3600 / 46 = 78.
This tells us that in one hour, the furnace would consume
78 cu. ft. of gas.
