Periodically, conventional gas-fired heating systems needadjustment to keep them runningin the safest, most efficient and least costly manner. Thispublication is designed to helpyou understand how gas-fired heating systems work (bothforced air and hot water systems), the periodic preventive maintenancethe units should have, and what special tasks and problems need the attention of a heating contractor.

Greg Tuttle, Graduate Student, Department of Agricultural Engineering Susan Mireley, Associate Professor and Extension Housing Specialist Department of Human Environment and Design

All gas-fired heating systems products elimination systemare composed of a heat- (exhaust stack, flue or chimney);producing source (a furnace in and control mechanisms (suchthe case of forced air systems as the thermostat, gas controland a boiler for hot water systems) valve and safety control devices).that contain both a burner and a Understanding how these variousheat exchanger; a distribution parts operate and work togethersystem (ducts in the case of forced is an important part of any air systems, pipes in hot water preventive maintenance systems); a burner by- program.

This publication covers maintenance ofconventional gas-fired heating systems only.Maintenance and repair of the newercondensing gas furnaces are not covered.Many of the same procedures andmaintenance activities described in thispublication are applicable if propane (L.P.gas) is used as the heating fuel. The orifices(the mechanism controlling the amount anddirection of the gas flowing to the burners)and the pressure regulator must be changedto convert a natural gas unit to propane. Asa unit is converted, a label should be added

HOW A GAS-FIRED HEATING SYSTEM WORKS

How the Typical Gas Burner Works When a room thermostat is turnedup or the room temperature dropsbelow the thermostat setting, theunit signals the furnace or boiler thatadditional heat is needed. As aresult of the signal, the gas controlvalve opens, allowing gas to flowinto the mixing tubes (see Fig. 1),where it mixes with the incomingcombustion air. The fuel/air mixturethen flows to the burners, where it isignited by either a pilot light or anelectronic spark. Ignition occursonly during start-up. Once started,the flames continue

to burn , with additional gas and airfed to the burners by the gas supplyline, the air shutters and furnace/boiler room air. In turn, thecombustion gases from the flamesflow through the flue passages of theheat exchanger, heating it, and thencontinue to flow up and out theexhaust stack (see Fig. 2 for a forcedair distribution system and Fig. 3 for ahot water distribution system). In themeantime, heat is transferred fromthe flue gases in the heat exchangerto the medium (either air or water)that flows through the distributionsystem that supplies heat to thevarious parts of the home.

How A TypicalForced Air DistributionSystem Works

When the air temperature in theheat exchanger reaches apredetermined temperature, which iscontrolled by the fan-and-limit control,the furnace blower begins pulling coolroom air through the return air regis-ters and ducts (see Figs. 2 and 4). Theair is passed through an air filter toremove dust. It then passes throughthe heat exchanger, as describedabove, where it is warmed by hotcombustion gases passing through theheat exchanger on their way out of thehouse. The furnace blower then forcesthe warm supply air into a plenum andthrough the supply ducts, finallydistributing it through supply registerslocated in each room in the home. Thetwo air supplies, the combustion airand the air distributed through thehouse supply system, should nevercome in direct contact with eachother.

How A Hot Water DistributionSystem Works

When a house thermostat calls forheat from a hot water distributionsystem, the circulator pump isactivated (see Fig. 3) and supplies hotwater held in reserve in the boilerthroughout the distribution system-through the supply main, the supplybranches and finally the baseboardunits (i.e., radiators or convectors insome systems) in the various rooms(see Fig. 5). As cool room air passesover the warmed baseboard unitsurfaces, the air absorbs heat and dis-tributes 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 and back to the boiler. When the water in the boilerdrops below a predeterminedtemperature, the aquastat activatesthe burner (see Fig. 3). The heatgiven off by the burner warms theheat exchanger and rewarms thewater in the boiler, which holds it inreserve until the circulator pumpmoves it through the distributionsystem once again. This two-phaseprocess enables the system tomaintain an on-demand supply ofhot water at all times. Thehomeowner doesn't have to waitfor the water to be reheated andcirculated through the system.

During the heating season,furnaces and boilers canaccumulate a buildup of dirt Inaddition, the various moving partswear. Dirt and water can lead to aloss of system efficiency, systemfailures, and health and safetyproblems. Annual inspections andmaintenance are required to keep agas-fired heating system operatingefficiently and safely. You can do a number ofmaintenance tasks yourself. Youmay want to ask your heatingcontractor to show you some of theprocedures during his or her nextvisit, or consult your heating systemowner's manual. It should providean excellent guide to the activitiesdo-it-yourselfers can do. Thispublication describes some of thoseactivities in a

MAINTENANCE AND INSPECTION YOU CAN DO

general way, but the owner'smanual will give you specificsfor your system. If the owner's manual is notavailable, write to themanufacturer and request thatone be sent to you. You willfind the manufacturer's nameand probably the address on thenameplate affixed to your unitsomewhere..If themanufacturer'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,give the model and serialnumber of your unit so thecorrect owner's manual can besent to you. Both numbers canbe found on the unit'snameplate. If you are a novice do-it-yourselfer, follow themanufacturer'srecommendations carefully anddo only those tasks the manualexplains clearly. All othersshould be done by a heatingcontractor. Gas is a clean,efficient and safe fuel if theequipment burning it is wellmaintained by knowledgeable

people. Novices andinexperienced tinkerers shouldbe aware of the potential forcreating problems.

The Furnace/Boiler 1. Inspect the pilot flameheight and color (see Figs. 1and 6). Check your unit'sowner's manual for theprocedure and the correctheight. The flame should beblue and fairly sharp. If it isn't,or if it seems too high or toolow, have a heating contractoradjust it. Some gas burners mayhave a spark ignition unit inplace of a standing pilot light.This is an energy-savingfeature that helps cut gasconsumption and so saves onheating bills. 2. Inspect the flame color ofthe burners and the pilot light(see Fig. 1). A natural gasflame should be primarily bluishand it should be fairly sharplydefined. (It you are burningpropane, the tips of the flameshould be yellow.) If theflameis lazy or yellow, the burnersshould be cleaned or the gas-to-air ratio in the mixing tubesneeds to be adjusted. Contact a

heating contractor to clean theunit and adjust the amount ofair entering the system throughthe air shutters. 3. Gas is a clean-burning fuel.If during your inspections younotice greasy dirt or soot builtup on the burners, a problem ispresent. Call your heatingcontractor to locate and repairit. 4. Clean the draft hood (seeFig. 1), the mechanism thatcontrols the rate at whichcombustion gases are pulled upand out of the flue or chimney.Dust buildup can interfere withthe hood's efficient operation.Vacuum any loose dust. Note:on some gas burners, the drafthood is incorporated into thebody of the unit and may not bedirectly visible. Your owner'smanual will explain the locationand any care it needs. 5. Inspect the exhaust stackfor bad connections anddamaged or corroded pipes(see Figs. 1, 2 and 3). Have aheating contractor replace anydamaged parts. 6. Inspect the furnace's/ boiler's electrical system(master switch and electricalcable, for example). Electricalproblems affect theperformance of a unit and alsopresent a safety hazard. Badconnections, bare wires, blownfuses or tripped circuit breakersindicate that an electricalproblem is present. Contactyour heating and coolingcontractor to correct it.(Warning: electricity ispotentially dangerous for peoplenot familiar with its operation.Use care in trying to correctany problems yourself.) If youever notice damaged wires infront of the burners, contactyour heating contractor.

7. Clean the furnace roomperiodically. Dirt and lint fromareas surrounding the unit canbe pulled into the burners alongwith combustion air. Eventuallythey will slow the movement ofcombustion air to the unit,causing it to burn inefficientlyand give off soot. 8. Clean the roomthermostat(s). Dust buildupinterferes with efficientthermostat operation. Removethe cover and wipe away dustwith a soft brush, such as awatercolor paint brush. Workcarefully-thermostats arefragile. 9. Inspect any visible sectionsof the chimney and thechimney top. If they are wornor damaged, consult yourheating contractor. 10. Safety note: gas-fired- furnaces and boilers require anadequate supply of air toensure proper and safe burningof the fuel. In addition,adequate clearances arenecessary betweencombustibles such as walls,doors and framing membersand the furnace/boiler, the ventstack and the chimney. Neverenclose a unit unless you checkwith a heating contractor aboutthe unit's combustion air needs.Never store combustiblematerials near the unit.

Forced Air Distribution System 1. Clean the blower fan andthe blower housing and cleanand lubricate the blower fanshaft and the blower motor(see Fig. 2). Dust, dirt anddebris buildup affects theefficient operation and usefullife of these components.Remove it with a vacuum orsoft cloth and lubricateaccording to your owner'smanual. (Note: some newerunits may not requirelubrication because the

bearings are sealed.) Warning:shut off electricity to the unitbefore starting theseprocedures. 2. Inspect the blower fan beltfor wear and correct tension(see Fig. 2). It is fairly commonfor the belt to be too tight,which can lead to failure of themotor or fan bearings. On theother hand, a loose belt can slip,causing faster belt wear andpremature belt failure. Replacethe belt when slippage can nolonger be corrected or beltfailure seems likely. Adjust thebelt tension according to yourfurnace's owner's manual.Warning: shut off electricity tothe unit before starting beltadjustment. (Note: many newergas furnaces do not have a fanbelt-a motor drives the fandirectly.) 3. Replace the air filterperiodically to ensure that air iscirculating freely and cleanly(see Fig. 2). Dirty air filtersslow air movement, make otherfurnace components workharder (which shortens theiruseful life) and waste energy.Inspect them monthly todetermine how often theyshould be changed. Followdirections provided in thefurnace owner's manual. 4. Inspect duct work for airleaks that result in heat loss andwasted money (see Fig. 4).Locate them by running yourhand over areas where yoususpect leaks. Seal leaks withduct tape. 5. Clean and clear roomsupply and return air registersof any dust or obstructions (seeFig. 4). They reduce aircirculation and waste energydollars. A vacuum will do agood job. 6. Any warning signs notedduring the heating season suchas unusual odors from the registers, discoloration overregisters, excessive dirt in the

house air supply, or unusual cycling of the burner or fan orboth-should be reported to yourheating contractor. 7. Periodically throughout theheating season, make aconscious effort to listen toyour unit as it goes through aheating cycle. The normalprocedure is: the roomthermostat calls for heat, theburner goes on, the fan thenstarts. Both should remain onuntil the thermostat temperatureis satisfied. Once it is satisfied,the burner stops first, followedby the fan. If the burner or thefan or both cycle on and offfrequently before thethermostat is satisfied, aproblem exists. Consult yourheating contractor. Likewise, ifthe burner ever goes on but thefan does not follow, call aheating contractor.

Hot Water Distribution System

1. Clean the circulator motorand lubricate the motor andcirculator pump (see Fig. 3).Dust and dirt buildup inhibitsefficient operation. Consultyour owner's manual forinstructions and lubricationneeds. 2. Clean and bleed baseboardunits (convectors or radiators insome systems; see Figs. 5 and7). Both dust and dirt buildup onthe baseboard unit's fins and airin the pipes decrease the heattransfer efficiency of thebaseboard unit. A vacuum anda softbristle brush work welltogether for cleaning the fins. Ifair is present in the pipes, you'llhear a sound similar to watertrickling. Bleed the unit byopening the air valve untilwater runs freely from the unit.Then close the valve. (Note:many modern hot watersystems contain automaticbleeders and do not require thisstep. Consult and follow your

owner's manual for the correctprocedures.) 3. Inspect baseboard units toensure that adequate clearanceexists between them and thefloor, particularly carpetedfloors. Clearance is necessaryto allow air to flow freelyaround the unit. If your handcannot slip easily into this area,consult a heating contractorabout raising the unit.

Though you can do themaintenance and repair tasksdescribed in your owner'smanual, other jobs require theknowledge of a heatingcontractor. Inexperiencedhomeowners attempting thesetasks may make mistakes thatexpose them and their familiesto unnecessary hazards andpossibly damage theequipment. We mention thesetasks because a heatingcontractor should do themduring a regular maintenancevisit. When selecting acontractor, ask about thestandard service proceduresfollowed and see if they aresimilar to those described here.We suggest that a heatingcontractor service your

system every two to three yearsand perhaps annually if thesystem is old. The cost will beapproximately $50 per visit.

The Furnace/Boiler 1. Inspect and clean theburners (see Fig. 1). They caneasily become plugged by dustor soot. Cleaning requiresspecial equipment. 2. Adjust the air shutters (seeFig. 1 ). The air shutters controland regulate the air/fuel mixturereleased for ignition andcombustion. Their correctadjustment improves overallfurnace efficiency and thushelps reduce energy costs. 3. Adjust the gas pressure tothe burner. The pressureaffects the volume of gasdelivered to the burner and,thus, the air/fuel mixture. 4. Inspect the gas controlvalve (see Fig. 1). This valvecontrols the amount of gasflowing into the system. Theheating contractor willdetermine if it is operatingcorrectly and inspect for leaksin the valve. 5. Inspect the thermocouple, asafety device designed to senseand shut down the gas supply tothe pilot flame if the pilot lightgoes out (see Figs. 1 and 6). Ifit is worn, the heatingcontractor will replace it. 6. Inspect and adjust safetydevices incorporated into theunit, such as the fan-and-limit switch or aquastat, burnersafety devices and any powerflue devices, if the unit containsa power draft. 7. Clean the heat exchangersurfaces (see Figs. 2 and 3).

Cleaning improves heattransfer between the heatexchanger and the householdair or water supply. 8. Check for gas leaks, whichare extremely dangerous.Serious health hazards arepossible if sufficient quantitiesof gas are released into thehome. Gas has a peculiar odor.If you ever suspect a leak,immediately leave the homeand contact your gas companyor service person from anearby phone. 9. Check for combustionleaks. Combustion leaks allowdangerous gases to escape intothe furnace room and ductwork.

Forced AirDistribution System 1. Align the blower pulley andthe blower motor pulley (seeFig. 2). Improper alignment can cause abnormal belt wearand slippage. (Note: mostnewer gas

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MAINTENANCE AND INSPECTION A SERVICE PERSON SHOULD DO

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furnaces do not have pulleys-amotor drives the fan directly.) 2. Adjust the blower fan speed(see Fig. 2). Overly high 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 the safety devicedesigned to shut the burners off ifthe 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 cooler airthrough the home and causeuncomfortable drafts.

To save energy, you may want toask your heating contractor tolower these two temperaturesettings to a level closer to thehouse thermostat setting. As aresult, the furnace will supplymore heat to the house but the airwill feel cooler. You mayexperience some draftiness anddiscomfort after the changes untilyou become accustomed to thenew settings.

Hot WaterDistribution System 1. Check the circulator pumpcoupler for wear and brokencoupler springs (see Fig. 3).Normally, if the coupler springsare broken, a loud racket occurs;they have been known to bebroken, however, with little noise. 2. Check the operation of allsafety controls (see Fig. 3), suchas the safety relief valve, whichwould relieve the system if overly

high pressure should occur becauseof overheating, and the limitthermostat, which would turn theunit off if the boiler shouldoverheat. 3. Check and adjust air andwater levels in the expansion tank,which provides a reservoir for thesafe collection of water as itexpands during the heating cycle(see Fig. 3). Note: many newexpansion tanks contain bladder ordiaphragm devices that controlwater and air levels automatically.

Sources:

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

Energy, Mines and ResourcesCanada. "The Billpayer's Guide toHeating Systems.'' Minister of

Supply and Services, Canada,1983. Knight, Paul A. MechanicalSystems Retrofit Manual.- AGuide for Residential Design.New York: VanNostrand Reinhold Company, 1987. Mireley, Susan and Don D.Jones. "The Indiana Do It YourselfHome Maintenance Checklists:Space Conditioning Systems," HE-63. Indiana Cooperative ExtensionService, Purdue University, July1986.