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Manifold Gas Pressure
Gas
Natural
High Stage
Propane
High Stage
G
I
R
M
AS
NPUT
ATE
EASUREMENT
The actual gas input rate to the furnace must never be greater
than that specified on the unit rating plate. To measure natu-
ral gas input using the gas meter, use the following proce-
dure.
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.
This tells us that at this rate, it would take 46 seconds to
consume one cu. ft. of gas. 23 x 2 = seonds per cu. ft.
3600 (secs in 1 hour) / 46 = 78
This tells us that in one hour, the furnace would consume 78
cu. ft. of gas.
The typical caloric 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.
T
R
EMPERATURE
ISE
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 air-
flow and temperature rise table is provided in the Specifica-
tion 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.
Range
Nom inal
3.2 - 3.8" w .c.
3.5" w .c.
9.5 - 10.5" w .c.
10.0" w .c.
(N
G
O
)
ATURAL
AS
NLY
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.
TEMPERATURE RISE
Model
*MVM970603BNAA
*MVM970803BNAA
*MVM970804CNAA
*MVM971005CNAA
*MVM971205DNAA
*CVM970603BNAA
*CVM970803BNAA
*CVM970804CNAA
*CVM971005CNAA
Temperature Rise Measurement
Figure 52
HI / LO
20-50/25-55
30-60/25-55
25-55/25-55
35-65/25-55
35-65/30-60
35-65/30-60
35-65/35-65
35-65/35-65
35-65/30-60
SUPPLY
AIR
RETURN
AIR
43
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