gas piping drip leg. The supply pressure must be measured with the burners operating. To measure the gas supply pressure, use the following procedure.
With Power and Gas Off:
1.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 the Inlet Gas Supply Pressure table below, make necessary pressure regulator adjustments, check piping size, etc., and/or consult with local utility.
Gas Line
Gas
Shutoff
Valve
Gas Line
To Furnace
Open To
Atmosphere
Drip Leg Cap
With Fitting
Manometer Hose
Manometer
Measuring Inlet Gas Pressure (Alternate Method)
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:
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| Gas | Range | Nominal | ||
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Natural |
| Low Stage | 1.6 - 2.2" | w.c. | 1.9" w.c. |
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| High Stage | 3.0 - 3.6" | w.c. | 3.5" w.c. |
Propane |
| Low Stage | 5.7 - 6.3" | w.c. | 6.0" w.c. |
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| High Stage | 9.7 - 10.3" w.c. | 10.0" w.c. | |
The final manifold pressure must not vary more than ± 0.3 “ w.c. from the above specified pressures. Any necessary major changes in gas flow rate should be made by changing the size of the burner orifice.
5.To adjust the gas valve pressure regulator, remove the regulator cap
6.Turn the adjustment screw clockwise to increase the pressure, or counterclockwise to decrease the pressure.
7.Securely replace the regulator cap.
8.Turn OFF gas to furnace at the manual shutoff valve and disconnect manometer.
9.Reinstall gas valve outlet pressure tap plug before turning on gas to furnace.
GAS INPUT RATE MEASUREMENT (NATURAL GAS ONLY)
3. Turn ON the gas supply and operate the furnace and all | The gas input rate to the furnace must never be greater than that | ||||||||||
| other gas consuming appliances on the same gas supply | ||||||||||
| specified on the unit rating plate. To measure natural gas input | ||||||||||
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| using the gas meter, use the following procedure. | ||||
4. Measure furnace gas supply pressure with burners firing. | |||||||||||
| 1. Turn OFF the gas supply to all other | ||||||||||
| Supply pressure must be within the range specified in the |
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| revolution of the smallest gas meter dial. | |
| Natural Gas | Minimum: | 5.0" w.c. |
| Maximum:10.0" w.c. |
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| 3. Calculate the number of seconds per cubic foot (sec/ ft3) of | |||||||
| Propane Gas | Minimum: 11.0" w.c. |
| Maximum:13.0" w.c. |
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If supply pressure differs from table, make the necessary |
| gas being delivered to the furnace. If the dial is a one cubic | |||||||||
| foot dial, divide the number of seconds recorded in step 2 | ||||||||||
adjustments to pressure regulator, gas piping size, etc., and/or |
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consult with local gas utility. |
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5. Turn OFF gas to furnace at the manual shutoff valve and |
| 4. Calculate the furnace input in BTUs per hour (BTU/ hr). Input | |||||||||
| disconnect manometer. | Reinstall plug before turning on |
| equals the sum of the installation’s gas heating value and a | |||||||
| gas to furnace. |
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| conversion factor (hours to seconds) divided by the number | |||
6. Turn OFF any unnecessary gas appliances stated in step |
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GAS MANIFOLD PRESSURE MEASUREMENT AND ADJUSTMENT |
| EXAMPLE: | |||||||||
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| Installation’s gas heating (HTG) value: 1,000 BTU/ft3 | |
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| Installation’s seconds per cubic foot: 34 sec/ ft3 | |||
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TO PREVENT UNRELIABLE OPERATION OR EQUIPMENT DAMAGE, THE GAS |
| Conversion Factor (hours to seconds): 3600 sec/hr | |||||||||
MANIFOLD PRESSURE MUST BE AS SPECIFIED ON THE UNIT RATING PLATE. |
| Input = (Htg. value x 3600) ÷ seconds per cubic foot | |||||||||
ONLY MINOR ADJUSTMENTS SHOULD BE MADE BY ADJUSTING THE GAS VALVE |
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| Input = (1,000 BTU/ft3 x 3600 sec/hr) ÷ 34 sec/ ft3 | ||||||||||
PRESSURE REGULATOR. |
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Only small variations in gas pressure should be made by adjusting |
| Input = 106,000 BTU/hr | |||||||||
| This measured input must not be greater than the input | ||||||||||
the gas valve pressure regulator. The manifold pressure must be |
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| indicated on the unit rating plate. | ||||||||||
measured with the burners operating. To measure and adjust the |
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| 23 | 12/04 | |||||||
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