HP 422690 I manual Manifold Pressure Adjustment, Checking GAS Input Rate, Natural GAS Input Rate

SECTION 13. MANIFOLD

PRESSURE ADJUSTMENT

You will need a 0 to 15 inch water manometer with 0.1 inch resolution and a 1/8" NPT manual shut-off valve to measure actual manifold pressure.

WARNING: Correct manifold pressure is necessary for proper ignition and burner operation. Failure to accurately adjust pressure could cause heat exchanger failure.

Check gas -supply pressure first. Follow instructions in Section 12, "Gas Supply Pressure and Pilot Adjustment."

1.Turn off gas at equipment shut-off valve in gas supply line just ahead of furnace.

2.Remove three screws holding burner access panel in place. Remove burner access panel.

3.Remove plug from manifold pressure tap in gas control. See Figure 13.

4.Install 1/8" NPT manual shut-off valve in hole vacated by plug. Make sure shut-off valve is in off position.

5.Attach manometer to 1/8" NPT manual shut-off valve just installed.

6.Slowly open equipment shut-off valve in gas supply line just ahead of furnace. Start furnace following "Operating Instructions" on front door.

7.Slowly open 1/8" NPT manual shut-off valve leading to manometer.

8.Read manifold pressure on manometer.

9.Adjust manifold pressure by turning gas control regulator adjusting screw clockwise to increase pressure or turning counter-clockwise to decrease pressure. Manifold pressure must be within allowable range below:

??Natural gas manifold pressure must be between 3.2 and 3.8 inches W.C.

??Propane gas (LP) manifold pressure must be between 9.7 and 10.3 inches W.C.

NOTE: For natural gas, if gas flow rate cannot be properly set within these pressure ranges then you must change main burner orifices to obtain proper gas flow rate.

10.Shut off furnace. Turn off gas at equipment shut-off valve in gas supply line just ahead of furnace. Install outlet-pressure-tap plug in gas control. Turn on gas.

11.Check regulator-adjustment-cover screw and gas control plug for gas leaks. Use a commercial soap solution made for leak detection.

12.Replace burner access panel using three screws removed in step 2.

SECTION 14. CHECKING GAS INPUT RATE

It is the installer's responsibility to see that the Btu input rate of the furnace is properly adjusted. Under-firing could cause inadequate heat, primary heat exchanger corrosion and/or ignition problems. Over-firing could cause sooting, flame impingement and/or overheating of heat exchanger.

WARNING: Failure to adjust furnace to the proper firing rate could cause heat exchanger failure.

Depending on your local gas heating value and elevation, you may need to adjust manifold pressure or change orifices to get proper gas input rate. Check with your local gas supplier to determine heating value (Btu/cu.ft.) of natural gas in your area.

NOTE: If furnace is being installed at an altitude of more than 2000 feet above sea level, you must derate the furnace. See Section 15, "Derating For High Altitude."

NATURAL GAS INPUT RATE

Natural gas heating value (Btu/cu.ft.) can vary significantly. Before starting natural gas input check, obtain gas heating value at your location from local supplier. You will need a stopwatch to measure actual gas input.

1.Gas supply pressure must be between 5 and 7 inches W.C. for natural gas. See Section 12, "Gas Supply Pressure and Pilot Adjustment."

2.Turn off all other gas appliances. You may leave pilots on.

3.Start furnace following "Operating Instructions" on front door. Let furnace warm up for 6 minutes.

4.Locate gas meter. Determine which dial has the fewest cubic feet of gas and how many cubic feet per revolution it represents. This is usually one-half, one or two cubic feet per revolution.

5.With stopwatch, measure time it takes to consume two cubic feet of gas.

??If dial is one cubic foot per revolution, measure time for two revolutions.

??If dial is two cubic feet per revolution, measure time for one revolution.

6.Divide this time by two. This gives average time for one cubic foot of gas to flow through meter. Example: If it took 58 seconds for two-cubic feet to flow, it would take 29 seconds for one-cubic foot to flow.

7.Calculate gas input using this formula: