Gas Input Rate Measurement (Natural Gas Only); Temperature Rise - Goodman GMH8 Installation Instructions Manual

1. Turn OFF gas to furnace at the manual gas shutoff valve
external to the furnace.
2. Turn off all electrical power to the system.
3. Back outlet pressure test screw (inlet/outlet pressure boss)
out one turn (counterclockwise, not more than one turn).
4. Attach a hose and manometer to the outlet pressure boss
of the valve.
5. Turn ON the gas supply.
6. Turn on power and energize main (M) solenoid. Do not
energize the (HI) solenoid.
7. Measure gas manifold pressure with burners firing. Adjust
manifold pressure using the Manifold Gas Pressure table
shown below.
8. Remove regulator cover screw from the low (LO) outlet
pressure regulator adjust tower and turn screw clockwise
to increase pressure, or counterclockwise to decrease
pressure.
9. Energize main (M) solenoid as well as the (HI) terminal.
10. Remove regulator cover screw from the (HI) outlet pressure
regulator adjust tower and turn screw clockwise to increase
pressure, or counterclockwise to decrease pressure.
11. Turn off all electrical power and gas supply to the system.
12. Remove manometer hose from outlet pressure boss.
13. Turn outlet pressure test screw in to seal pressure port
(clockwise, 7 in-lb minimum).
14. Turn on electrical power and gas supply to the system.
15. Turn on system power and energize valve.
16. Using a leak detection solution or soap suds, check for
leaks at pressure boss screw. Bubbles forming indicate a
leak. SHUT OFF GAS AND FIX ALL LEAKS IMMEDIATELY.
NOTE: For gas to gas conversion, consult your dealer for
appropriate conversion.
Manifold Gas Pressure
Gas Rate
Natural Low Stage
High Stage
Propane Low Stage
High Stage
Range
1.7 to 2.3" w.c.
3.2 to 3.8" w.c.
5.7 to 6.3" w.c.
9.7 to 10.3" w.c.
Nominal
2.0" w.c.
3.5" w.c.
6.0" w.c.
10.0" w.c.
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 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 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 BTUIft s
(Obtained from gas supplier)
Installation's seconds per cubic foot: 34 sec/ft s
Conversion Factor (hours to seconds): 3600 sec/hr
Input = (Htg. value x 3600) + seconds per cubic foot
Input = (1,000 BTUtft 3 x 3600 sec/hr) + 34 sect ft s
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
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 Product Data Book
applicable to your model. (Please contact your distributor or our
website for the applicable product data book referred to in this
manual.)
HEAT EXCHANGER
RADIATION "LINE OF SIGHT"
"3
i T_U_L_
R_SE = Tsu_ _ TRETURN
T_ETURN
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.
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