Instruction manual

23
Only small variations in gas pressure should be made by adjusting
the gas valve pressure regulator. The manifold pressure must be
measured with the burners operating. To measure and adjust the
manifold pressure, use the following procedure.
1. Turn OFF gas to furnace at the manual gas shutoff valve
external to the furnace.
2. Connect a calibrated water manometer (or appropriate gas
pressure gauge) at the gas valve outlet pressure tap (refer to
gas valve figure in previous section).
3. Turn ON the gas supply and operate the furnace.
4. Measure gas manifold pressure with burners firing. Adjust
manifold pressure according to the table below:
Gas Range Nominal
Natural 3.2 to 3.8" w.c. 3.5" w.c.
Propane 9.7 to 10.3" w.c.
10.0" w.c.
Manifold Gas Pressure
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 us-
ing 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 one cubic
foot dial, divide the number of seconds recorded in step 2 by
one. 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 sum of the installation’s gas heating value and 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) ÷ seconds per cubic foot
Input = (1,000 BTU/ft
3
x 3600 sec/hr) ÷ 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.
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 overheat-
ing of the heat exchanger. Determine and adjust the temperature
rise as follows. The temperature rise must be within the range speci-
fied on the rating plate or Product Data Bulletin.
With Power and Gas Off:
1. Honeywell Model VR8205, or White-Rodgers Models 36E22,
or White-Rodgers Model 36F22: Connect a water manometer
or adequate gauge to the “inlet pressure tap” of the gas valve.
As an alternative method, inlet gas pressure can also be
measured by removing the cap from the drip leg and installing
a predrilled cap with a hose fitting (Figure 26).
With Power and Gas On:
2. Put furnace into heating cycle and turn on all other gas
consuming appliances.
If operating pressures differ from above, make necessary pressure
regulator adjustments, check piping size, etc., and/or consult with
local utility.
Gas Line
Gas
Shutoff
Valve
Gas Line
To Furnace
Drip Leg Cap
With Fitting
Manom eter Hose
Manometer
Open To
Atmosphere
Figure 26 - Measuring Inlet Gas Pressure
(Alternate Method)
3. Turn ON the gas supply and operate the furnace and all other
gas consuming appliances on the same gas supply line.
4. Measure furnace gas supply pressure with burners firing.
Supply pressure must be within the range specified in the
table below.
Natural Gas
Minimum: 5.0" w.c. Maximum:10.0" w.c.
Propane Gas
Minimum: 11.0" w.c. Maximum:13.0" w.c.
Inlet Gas Supply Pressure
If supply pressure differs from table, make the necessary adjust-
ments to pressure regulator, gas piping size, etc., and/or consult
with local gas utility.
5. Turn OFF gas to furnace at the manual shutoff valve and
disconnect manometer. Reinstall plug before turning on gas
to furnace.
6. Turn OFF any unnecessary gas appliances started in step 3.
GAS MANIFOLD PRESSURE MEASUREMENT AND ADJUSTMENT
CAUTION
T
O PREVENT UNRELIABLE OPERATION OR EQUIPMENT DAMAGE, THE GAS
MANIFOLD PRESSURE MUST BE AS SPECIFIED ON THE UNIT RATING PLATE.
O
NLY MINOR ADJUSTMENTS SHOULD BE MADE BY ADJUSTING THE GAS VALVE
PRESSURE REGULATOR.