Manual 2100-483EPage 27 of 5919. MANIFOLD PRESSUREADJUSTMENTYou will need a 0 to 15 inch water manometer with 0.1inch resolution and a 1/8" NPT manual shut off valve tomeasure actual manifold pressure.Depending on your local gas heating value andelevation, you may need to adjust manifold pressure orchange orifices to get proper gas input rate. Checkwith 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 ofmore than 6,000 feet above sea level, youmust derate the furnace. See Section 21“Standard Orifice Sizing and High AltitudeDerate”.20. CHECKING GAS INPUT RATEIt is the installer's responsibility to see that the BTUinput rate of the furnace is properly adjusted. Under-firing could cause inadequate heat, excessivecondensation or ignition problems. Overfiring couldcause sooting, flame impingement or overheating ofheat exchanger.1. Turn off gas at equipment shut off valve in gassupply line just ahead of furnace.2. Remove plug from outlet pressure tap in gas controlor gas manifold.3. Install 1/8" NPT manual shut off valve in holevacated by plug. Make sure shut off valve is in offposition.4. Attach manometer to 1/8" NPT manual shut offvalve just installed.PROPANE (LP) GAS CONVERSIONThis unit may be converted in the field foruse with Propane (LP) gas. Propane gasconversion kit number WGCK-1 is designedfor conversions of units installed from0 – 6,000 feet elevations. Propane gasconversion kit number WGCK-2 is designedfor conversions of units installed from 6,001– 10,000 feet elevations. These kits maybe purchased from your local distributor.5. Slowly open equipment shut off valve in gas supplyline just ahead of furnace. Start furnace following“Operating Instructions” on front door.6. Slowly open 1/8" NPT manual shut off valve leadingto manometer.7. Read manifold pressure on manometer.8. Adjust manifold pressure by turning gas controlregulator adjusting screw clockwise to increasepressure or turning counterclockwise to decreasepressure. Manifold pressure must be withinallowable range as follows:• Natural gas manifold pressure must be between3.2 and 3.8 inches W.C. Rated pressure is 3.5inches.• Propane gas (LP) manifold pressure must bebetween 9.7 and 10.3 inches W.C. Ratedpressure is 10 inches.NOTE: For natural gas, if gas flow rate can't beproperly set within these pressure rangesthen you must change main burner orifices toobtain proper gas flow rate.9. Shut off furnace. Turn off gas at equipment shut offvalve in gas supply line just ahead of furnace. Installoutlet pressure tap plug in gas control. Turn on gas.10. Check regulator adjustment cover screw and gascontrol plug for gas leaks. Use a commercial soapsolution made for leak detection.WARNINGFailure to adjust furnace to the proper firingrate could cause heat exchanger failure.WARNINGWhen converting from propane (LP) gas tonatural gas, the gas orifice spuds and gasvalve spring must be replaced and the gasvalve regulator pressure must be adjustedcorrectly. Failure to do so can result in fire,injury or death. Refer to Tables 8 and 8A forproper orifice sizing.Natural gas spring kit, Part number 5603-007,can be purchased through your localdistributor.WARNINGCorrect manifold pressure is necessary forproper ignition and burner operation. Failureto accurately adjust pressure could causeheat exchanger failure.