Maintaining ConventionalResidential Oil-Fired

Heating Systems

Greg Tuttle, Graduate Student, Department of Agricultural EngineeringSusan Mireley, Associate Professor and Extension Housing Specialist

Department of Human Environment and Design

This publication covers maintenance of conventional oil-fired heating systems only Information on maintenance and repair of the newer oil furnaces is not covered.

Periodically, oil-fired heatingsystems need adjustment to keepthem running in the safest, mostefficient and least costly manner.This publication is designed to helpyou understand how oil-firedheating systems work (both forcedair and hot water systems), whatperiodic preventive maintenancetasks the units should have, andwhat special tasks and problemsmight arise that would need theattention of a heating contractor.

All oil-fired heating systems arecomposed of a heat producingsource (a furnace in the case offorced air systems and a boiler forhot water systems)

heat exchanger; a distribution system (ducts in the case of forcedair systems, pipes in hot water systems); a burner by-productselimination system (exhaust stack,flue or chimney); and controlmechanisms (such as the thermostatand master switch). Understandinghow these various parts operate andwork together is an important part ofany preventive maintenanceprogram.

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HOW AN OIL-FIRED HEATING SYSTEM WORKS

How the Typical Oil Burner Works When a room thermostat isturned up or the room temperaturedrops below the thermostat setting,the unit signals the furnace orboiler that additional heat isneeded. As a result of the signal,the burner motor activates the fueloil pump, sending fuel oil to anozzle at the end of an air tube(see Figs. 1 and 2). Under highpressure, the fuel oil is pushedthrough the nozzle to form a finemist. At the same time, the burnerblower, also operated by theburner motor, blows room air intothe same air tube. The two-the airand the fuel oil mist-combine toform a highly flammable vapor thatis then ignited by a spark suppliedby the ignition electrodes. Oncestarted, the flames continue to burnin the combustion chamber withadditional fuel oil and room airsupplied through the air tube/nozzle. In turn, the combustiongases from the flame flow throughthe flue passageways of the heatexchanger, heating it, and thencontinue to flow up and out theexhaust stack (see Fig. 1 for aforced air distribution system andFig. 2 for a hot water distributionsystem). In the meantime, heat istransferred from the flue gasesthrough the heat exchanger wallsto the heat distribution medium(either air or water) that flowsthrough the supply system,distributing heat to various parts ofthe home.

How a Typical Forced AirDistribution System Works

When the air temperature in theheat exchanger reaches apredetermined temperature, whichis controlled by a fan-and-limit

control, the furnace blower beginspulling cool room air through thereturn air registers and ducts (seeFigs. 1 and 3). The air is passedthrough a filter to clean it of dust.It then passes through the heatexchanger, as described above,where it is warmed by the hotcombustion gases passing throughthe heat exchanger on their wayout of the house. The furnaceblower then forces the warmsupply air into a plenum andthrough the supply ducts, finallydistributing it through supplyregisters in each room in the home.The two air supplies, thecombustion air and the airdistributed through the housesystem, should never come indirect contact with each other.

How a Hot Water DistributionSystem Works

When a house thermostat callsfor heat from a hot waterdistribution system, the circulatorpump is activated (see Fig. 2) andsupplies hot water held in reservein the boiler throughout thedistribution system-through thesupply main, the supply branches

During the heating season, furnaces and boilers canaccumulate a build-up of dirt.In addition, the various movingparts wear. Dirt and wear canlead to a loss of system efficiency,system failures, and health andsafety problems. Annual inspections and maintenanceare required to keep an oil-fired

and finally the baseboard units (i.e.,radiators or convectors in somesystems) in the various rooms (seeFig. 4). As cool room air passesover the warmed baseboard unitsurfaces, the air absorbs heat anddistributes it throughout the room.Individuals, furnishings and objectsnear the baseboard units are alsowarmed by heat given off by theunits. The now cool watercompletes the cycle, flowing fromthe baseboard units through thereturn branches and the returnmain back to the boiler.

When the water in the boilerdrops below a predeterminedtemperature, the aquastat activatesthe burner (see Fig. 2). The heatgiven off by the burner warms theheat exchanger and rewarms thewater in the boiler, which holds it inreserve until the circulator pumpmoves the water through thedistribution system once again.This two-phase process enablesthe system to maintain an on-demand supply of hot water at alltimes. The homeowner does nothave to wait for the water to bereheated and circulated through thesystem.

heating system operating efficiently and safely. You can doa number of the maintenance and inspection tasks yourself. You may want to ask your heatingcontractor to show you some ofthe procedures during his or hernext visit or consult your heatingsystem owner’s manual. It shouldprovide an excellent guide to the

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MAINTENANCE AND INSPECTION YOU CAN DO

types of activities do-it-yourselferscan do. This publication describessome of those activities in ageneral way, but the owner'smanual will give you specifics foryour system. If the owner's manual is notavailable, write to themanufacturer and request that onebe sent to you. You will find the

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manufacturer’s name and probably the address on the nameplateaffixed to your unit somewhere. Ifthe manufacturer's address is notavailable, consult your heatingcontractor or search the YellowPages to find the name of aheating contractor that sells thebrand you own. In your letter, givethe model and serial number ofyour unit so

the correct owner's manual can besent to you. Both numbers can befound on the unit's nameplate. If you are a novice do-ityourselfer, follow themanufacturer's recommendationscarefully, and do only those tasksexplained in the manual. All othersshould be done by a heatingcontractor. Oil is an efficient

and safe fuel if the equipmentburning it is well maintained byknowledgeable people. Novicesand inexperienced tinkerers shouldbe aware of the potential forcreating problems.

The Furnace/Boiler 1. Change the fuel oil filterperiodically (see Figs. 1 and 5).The fuel filter cleans the fuel ofany impurities (e.g., dirt and water)that may affect the efficient supply,ignition and burning of the fuel.Consult the owner's manual for thecorrect procedure. 2. Clean and lubricate the burnermotor (see Fig. 1). Dust and oilbuildup will shorten the life of the

burner motor. Vacuum away anyloose dust and wipe away any oilbuildup or greasy dirt. Lubricatethe burner motor according to yourowner's manual.

3. Inspect the burner mountingplate for evidence of leaks (seeFig. 1). They can alter the fuel/airmixture and allow smoke toescape into the room. If smudgesare present around the plate, callyour heating contractor to correctthe situation. 4. Inspect the furnace's/ boiler'selectrical system (i.e., masterswitch and electrical cable, seeFig. 1). Electrical problems affectthe performance of a unit and alsopresent a safety hazard. Bad

connections, bare wires, blownfuses, tripped circuit breakers andtripped reset buttons (the resetbutton automatically disconnectsthe electricity to an overloadedelectrical motor) indicate that anelectrical problem is present.Contact your heating C-6ntractorto correct it. (Warning: electricityis potentially dangerous for peoplenot familiar with its operation.Repairs should be made by aqualified service person.) 5. Inspect the exhaust stack forbad connections and damaged orcorroded pipes (see Figs. 1 and 2).Replace if damage is evident. 6. Clean the draft regulator,

the mechanism controlling the rateat which combustion gases arepulled up and out the exhaust stack(see Figs. 1 and 2). Soot and dustbuildup can interfere with the draftregulator's efficient operation.Vacuum any loose dust and wipeoff any greasy soot. Also clean theback side of the hinged plate. Anymodifications or changes in thedraft regulator setting should bedone by a qualified service person.

7. Inspect the fuel storage tankfor leaks. Clues include oil stains orpuddles and/or a strong odor in thevicinity of the tank. Call a heatingcontractor to replace the unit. 8. Clean the furnace roomperiodically. Dirt and lint fromareas surrounding the unit can bepulled into the burner along withcombustion air. Eventually they willslow the movement of combustionair to the unit, causing it to burninefficiently and give off soot. 9. Clean and adjust the roomthermostats. Dust buildup interfereswith efficient thermostat operation.Remove the cover and wipe awaydust with a soft brush, such as awatercolor paint brush. Workcarefully- thermostats are fragile. 10. Observe the color of smokeleaving the chimney. Black smokeis a sign of poor combustion. Call aheating contractor to make neededadjustments. 11. Inspect any visible sections ofthe chimney and the chimney top.If they are worn or damaged,consult your heating contractor. 12. Most oil furnaces areequipped with a reset buttonlocated on either the stack controlor the primary control-the safetydevices that shut the burner off ifa flameless condition exists. Stack

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controls are found on older units,while primary controls are foundon newer ones. If the reset buttontrips the burner off, a fuel supplyor ignition problem has occurred.Push the reset button once torestart the burner. If the resetbutton trips the burner off again,contact your heating contractor. 13. Safety note: oil-fired furnacesand boilers require an adequatesupply of air to ensure proper andsafe burning of the fuel. Inaddition, adequate clearances arenecessary between combustiblessuch as walls, doors and framingmembers and the furnace/boiler,the vent stack and the chimneyNever enclose a unit unless youcheck with a heating contractorabout the unit's combustion airneeds. Never store combustiblematerials near the unit.

Forced Air Distribution System 1. Clean the blower fan and theblower housing and clean andlubricate the blower fan shaft andthe blower motor (see Fig. 1).Dust, dirt and debris buildupaffects the efficient operation anduseful life of these components.Remove it with a vacuum or softcloth and lubricate according toyour owner's manual. (Note: somenewer units may not requirelubrication because the bearingsare sealed.) Warning: shut offelectricity to the unit beforestarting these procedures. 2. Inspect the blower fan belt for

wear and correct tension (see Fig.1). It is fairly common for the beltto be too tight, which can lead topremature failure of the motor orfan bearings and possible beltbreakage. On the other hand, a loose belt can slip, causing fasterbelt wear and premature belt

failure. Replace the belt whenslippage can no longer becorrected or belt failure seemslikely. Adjust the belt tensionaccording to your furnace'sowner's manual. (Note: manynewer oil furnaces do not have afan belt-a motor drives the fandirectly.) Warning: shut offelectricity to the unit beforestarting belt adjustment. 3. Replace the air filterperiodically to ensure that air iscirculating freely and cleanly (seeFig. 1). Dirty air filters slow airmovement, make other furnacecomponents work harder (whichshortens their useful life), andwaste energy. Inspect themmonthly initially to determine howoften they should be changed.Follow directions provided in thefurnace owner's manual. 4. Inspect duct work for air leaks

that result in heat loss and wastedmoney (see Fig. 3). While the fanis operating, locate them byrunning your hand over areaswhere you suspect leaks. Sealleaks with duct tape. 5. Clean and clear the roomsupply and return air registers ofany dust or obstructions (see Fig.3). They reduce air circulation andwaste energy dollars. A vacuumwill do a good job. 6. Any warning signs notedduring the heating season such asunusual odors from the registers,discoloration over registers,excessive dirt in the house airsupply, or unusual cycling of theburner or fan or both should bereported to your heatingcontractor. 7. Periodically throughout theheating season, make a consciouseffort to listen to your unit as itgoes through a heating cycle. Thenormal procedure is:

the room thermostat calls for heat,the burner goes on, the fan thenstarts. Both should remain on untilthe thermostat temperature issatisfied. Once it is satisfied, theburner stops first, followed by thefan. If the burner or the fan or bothcycle on and off frequently beforethe thermostat is satisfied, aproblem exists. Consult yourheating contractor. Likewise, if theburner ever goes on but the fandoes not follow, call a heatingcontractor.

Hot WaterDistribution System 1. Clean the circulator motor and lubricate the motor and circulator

pump (see Fig. 2). Dust and dirtbuildup inhibit efficient operation.Consult your owner's manual forinstructions and lubrication needs. 2. Clean and bleed baseboardunits (convectors or radiators insome systems; see Fig. 4). Bothdust and dirt buildup on thebaseboard unit's fins and air in thepipes decrease the heat transferefficiency of the baseboard unit. Avacuum and a softbristle brushwork well together for cleaning thefins. If air is present in the pipes,you'll hear a sound similar to watertrickling. Bleed the unit by opening the air valve until water runs freelyfrom the unit. Then close the valve.(Note: many modern hot water

systems contain automatic bleedersand do not require this step.Consult and follow your owner'smanual for the correctprocedures.) 3. Inspect baseboard units toensure that adequate clearanceexists between them and the floor,particularly carpeted floors.Clearance is necessary to allow airto flow freely around the unit. Ifyour hand cannot slip easily intothis area, consult a heatingcontractor about raising the unit.

MAINTENANCE AND INSPECTION A SERVICE PERSONSHOULD DO

Though you can do themaintenance and repair tasksdescribed in your owner's manual,other jobs require the knowledgeof a heating contractor.Inexperienced homeownersattempting these tasks may makemistakes that expose them andtheir families to unnecessaryhazards and possibly damage theequipment. We mention thesetasks because a heating contractorshould do them during a regularmaintenance visit. When selectinga contractor, ask about thestandard service proceduresfollowed and see if they are similarto those described here. Wesuggest that a heating contractorservice your system every year.The cost will be approximately $50per visit.

The Furnace/Boiler 1. Clean or replace the burnernozzle (see Fig. 1). With use, theburner nozzle passage ways maybecome partially blocked orenlarged. In either case, theamount of fuel oil being deliveredto the combustion chamber will notbe correct and the resulting fuel/airmixture will contain either toomuch or too little fuel. Bothconditions will lower the efficiencyof the furnace or boiler. 2. Clean the burner blower (seeFig. 1). Dirt buildup on the blowercauses an improper air/oil mixtureby cutting down on the amount ofair supplied to the unit and lowersthe efficiency of the burner. 3. Adjust the burner flame (seeFigs. 1 and 2). An improper burnerflame level will generate less heatper unit of fuel than the properflame could produce.

4. Inspect, clean and adjust theignition electrodes (see Fig. 1). Ifignition does not occur because ofa problem with the electrodes andthe fuel/air mixture continues to bepumped into the combustionchamber, an explosive conditionwill exist, an obvious safety hazard. 5. Inspect and clean thetransformer (see Figs. 1 and 2).The transformer amplifies theelectrical voltage supply (from 110to 120 volts to 5,000 to 10,000volts) to the electrodes, initiatingthe spark that starts combustion. 6. Adjust the air volume control(see Figs. 1 and 2). Thismechanism controls the amount ofair in the fuel/air mixture, a majorfactor affecting burner efficiency. 7. Inspect and adjust the fuel oilpump, which regulates the amountand the pressure of fuel oil in thefuel/air mixture (see Figs. 1 and 2).Improper calibration of the fuel oilpump decreases furnace or boilerefficiency. 8. Inspect, adjust and cleanstack control, a necessary safetydevice (see Figs. 1 and 2). If thefurnace or boiler is operating in a

flameless condition, the stackcontrol will shut down the burner.It needs to be functioning well atall times. (Newer units do not havea stack control. They have, instead,a solid state primary control, whichincorporates a cad cell, a light-sensitive mechanism that monitorselectricity to the burner, shuttingthe burner down if a flame is notproduced. The cad cell should beinspected for dirt and sootaccumulation and cleaned asneeded. It should also berealligned.) 9. Adjust the draft regulator (seeFigs. 1 and 2). Improperadjustment can result in excessiveheat loss up the flue. 10. Clean the heat exchangersurfaces (see Figs. 1 and 2).Cleaning improves heat transferbetween the heat exchanger andthe heating medium (the air orwater supply).

11. Check for combustion leaks.Combustion leaks allow dangerousgases to escape into the furnaceroom. 12. Perform efficiency tests andmake required adjustments.Efficiency tests help the contractordetermine burner efficiency andoverall furnace or boiler efficiencyand point to specific areas whereadjustments can be made toincrease efficiency. These testsare essential to ensure that your oilfurnace or boiler is running at itspeak level of performance.Because of their importance, thetests are described and explainedin more detail on pages 14-15.

Forced AirDistribution System 1. Align the blower pulley andthe blower motor (see Fig. 1).Improper alignment can causeabnormal belt wear and slippage.(Note: most newer oil furnaces donot have pulleys a motor drives thefan directly.)

2. Adjust the blower fan speed(see Fig. 1). Excessive fan speedwill cause duct noise and wasteelectricity. If the fan is setunnecessarily low, an excessiveamount of heat will be lost throughthe supply ducts before it reachesthe registers to provide room heat. 3. Adjust and test the fan-and-limit control, which measures thetemperature of the air surroundingthe heat exchanger. Itautomatically turns the furnaceblower on and off during eachburning cycle and shuts the burnerdown if the heat exchangerbecomes overly hot. The controlmonitors three temperatures: afan-on temperature, a fan-offtemperature and a temperaturelimit, which is a safety devicedesigned to shut the burner off if

the heat exchanger becomes toohot. It is never adjusted orchanged-the other two can be,however, For example, the fan-ontemperature is usually about 135degrees F. When the air aroundthe heat exchanger reaches thistemperature, the blower fan comeson and moves the heated airthroughout the home. The fan-offtemperature is usually set atapproximately 100 degrees F.When the air surrounding the heatexchanger reaches thistemperature, the fan blower stopsso it doesn't circulate cool airthrough the home and causeuncomfortable drafts. To saveenergy, you may want to ask yourheating contractor to lower thesetwo temperature settings to a levelcloser to the house thermostatsetting. As a result, the furnacewill supply more heat to the houseBUT the air will feel cooler. Youmay experience some draftinessand discomfort after the changesuntil you become accustomed tothe new settings.

Hot Water Distribution System 1. Check the circulator pumpcoupler for wear and brokencoupler springs (see Fig. 2). Thecoupler connects the motor withthe pump. Normally, if the couplersprings are broken, a loud racketoccurs; they have been known tobe broken, however, with littlenoise. 2. Check the operation of allsafety controls (see Fig. 2), such asthe safety relief valve, which wouldrelieve the system if overly highpressure should occur because ofoverheating. 3. Check and adjust air and waterlevels in the expansion tank, whichprovides a reservoir for the safecollection of water as it expandsduring the heating cycle (see Fig.2). Note: many new expansiontanks contain bladder or diaphragmdevices that control water and airlevels automatically.

OIL FURNACE OR BOILER EFFICIENCY TESTS

Efficiency tests are the best meansavailable to determine if your oilfurnace or boiler is functioning atits maximum efficiency level andthus providing you with the mostheating output for your energydollars. Efficiency tests indicatethe amount of heat output you arereceiving in relation to fuel inputinto the system. Efficiency tests should be doneby a heating contractor becauseperforming them and makingnecessary adjustments requiresspecialized knowledge. In addition,the equipment needed to performthem is specialized and

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relatively expensive. Four testsshould be conducted to ensure thata furnace achieves maximumefficiency. Efficiency tests are a series offlue gas measurements: a draftvolume measurement, a smoketest, a carbon dioxide (C02)percentage reading and a flue gastemperature reading. The first twotests are done to make burneradjustments, and the others providea measure of the overall efficiencyof the system. The equipmentrequired for these tests includes adraft gauge, a smoke tester, C02

indicator and a flue gas

thermometer. Two steps have to be taken

before conducting the tests. First, ahole must be drilled in the flue pipeclose to the body of thefurnace/boiler and ahead of thedraft regulator. This hole will beused to insert the test equipmentand provide readings. After thetests are completed, it can bereplugged with a sheet metalscrew. Second, immediately beforetesting, the furnace or boiler mustbe brought up to its normaloperating temperature. This can beaccomplished by turning the housethermostat above its normalreading for 10 to 15 minutes. Thetests are then conducted. The first test conducted measuresthe amount of draft or the speed ofthe movement of combustion gasesup the chimney. The test indicateshow forcefully the gases are beingmoved out of the house. The testprobe of the draft gauge is insertedinto the flue pipe hole and thereading recorded. A high draftreading indicates that the hot gasesare being drawn up the flue tooquickly and excessive heat is being wasted through the chimney. Alow draft reading, on the otherhand, indicates the gases are notbeing vented quickly enough. Tocorrect draft problems, the heatingcontractor will adjust air intake tothe burner and combustionchamber and the balance weighton the draft regulator door.

The second test is a smoke test,which indicates the soot content ofthe flue gases. The probe for thesmoke tester is inserted into theflue pipe hole and a specifiedamount of smoke is drawn throughfilter paper. The darkened filterpaper is then compared to a smoketest scale (ranging from 0 to 10)supplied with the test kit. Anythinghigher than 2 on the scale meansthe air/fuel mix is poor and anexcessive amount of unburned fuelis escaping up the chimney. Theheating contractor will adjust theair supply to the burner to achievea more smokeless flame. Measuring and adjusting thefurnace or boiler's draft andachieving a low smoke test numberset the stage for accurate C02 andstack temperature tests. Thesefinal two tests are used to calculatethe operating efficiency of the unit. The contractor measures the C02

content of the flue gas todetermine if excess air is presentin the flue. It is accomplished byinserting the C02 indicator probeinto the flue pipe hole andextracting a specified amount offlue gas. The reading shouldregister somewhere between 0 and14 percent. If the percentage ofC02 is low (less than 8 percent, forexample), the air/fuel mix is high inexcess air, and valuable heat isbeing wasted out the flue orchimney. The heating contractorshould adjust the air/fuel mixture. Finally, the flue gas temperatureis taken to determine the unit'sability to utilize heat and not wasteit. It is measured by inserting theflue gas thermometer into the fluepipe hole. A high flue gastemperature, such as 500 to 550degrees F or over, indicates an

excessive amount of heat isescaping up the chimney, thuswasting energy dollars. Lowtemperatures, on the other hand,such as 300 to 350 degrees F. orlower, indicate that corrosivecondensation may be occurring inthe chimney. The contractor willcorrect either situation. The results of the C02 and fluegas temperature tests are appliedto a chart similar to the one shownin Fig. 7, which provides anindication of furnace or boilerefficiency. The C02 percentagereading is located along thehorizontal line of the graph and theflue gas temperature is locatedalong the vertical line. The pointinside the graph where lines fromthese plotted points intersect

indicates furnace efficiency. Anefficiency percentage below 75percent indicates that the flue gastemperature is too high and thepercent C02 in the flue gas is toolow. We strongly urge that you have aheating contractor perform theefficiency tests annually. The costof hiring a contractor varies, but onthe average, it runs approximately$50 for a regular maintenancevisit. The contractor should be ableto estimate the time needed andthus the additional cost forconducting the tests. The potentialsavings on your annual heating billfrom the adjustments could verywell pay for the call and perhapssave some extra dollars as well.

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Sources:

Brotherson, Donald, Heating theHome, G3.1. Small HomesCouncil-Building ResearchCouncil, University of Illinois,1976.

Energy, Mines and ResourcesCanada. The Billpayer's Guide toHeating Systems. Minister ofSupply and Services Canada, 1983.

Knight, Paul A. MechanicalSystems Retrofit Manual: AGuide for Residential Design.New York: VanNostrand ReinholdCompany, 1987.

Mireley, Susan and Don D. Jones,The Indiana Do It YourselfHome Maintenance Checklists:Space Conditioning Systems,HE-63. Indiana CooperativeExtension Service, PurdueUniversity, July 1986.

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