Chapter 3 – Utility Systems – Heating and Air Conditioning · · 2018-01-27stand the basics of heating and air conditioning so ... Thermostat The thermostat ... This allows

Utility and General System Notes

This is where your homework starts. Take time toread these chapters. They contain important infor-mation about the many systems in your home. Theexplanation of each system includes operatinginformation, terminology, sketches, main shutoffs,and part names. If you need more specific informa-tion, check the References section.

Since some systems are very complicated, they needto be serviced routinely by contractors. Look in theService Checklists chapter for specifications you cancopy and use with service contractors. You can dosimple maintenance yourself; this information is pro-vided in utility systems chapters and in Chapter 8 onService Requirements by the Calendar.

Your home will not have all of the systems shownin this book. For instance, you may have a warmair furnace or a hot water furnace, but not both.You may have either a central air conditioner or aheat pump. As you read, walk around your hometo determine the type of equipment you have andidentify important valves and switches. If some sys-tems or parts are confusing, ask a professional serv-ice contractor or a knowledgeable friend to walkyou through the system.

The chapters on emergencies will help you solveproblems and perhaps avoid a service call. Manyemergencies, strange noises, leaks and smells havesimple solutions. I have attempted to include allcommon problems.

Heating and Air Conditioning

Most homes are heated with a warm air furnace(also called a forced air furnace) because this typeof system provides heating and cooling throughthe same air distribution ducts. A warm air systemrequires supply grills in most rooms. Some homesare heated with a hydronic (warm water) systemthat uses radiators, baseboard (convector) ele-ments, or heating pipes buried in walls or floors.

The energy source for heating can be natural gas,propane, or oil. In warmer climates, electrical resist-ance heating elements may be used in a warm airfurnace. Usually, the energy source for air condi-tioning is electricity, but gas-powered engine sys-tems can also provide cooling.

Some homes have separate heating and coolingsystems. One common system combines hydronicheating with ducted air conditioning.

As you review the information on heating and airconditioning, identify the system used in your home.

As with all systems in your home, you must under-stand the basics of heating and air conditioning soyou can perform basic maintenance and operatethe system properly and efficiently.

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Chapter 3 – Utility Systems – Heating and Air Conditioning

© Tom Feiza, Mr. Fix-It Inc. This is part of the book "How to Operate Your Home" by Tom Feiza. No part of this document may be reproduced or transmitted in any form without written permission from the author. For more information, visit www.htoyh.com.

http://www.htoyh.com

Thermostat

The thermostat provides automatic control for heat-ing and cooling systems. You set it to the tempera-ture you want to maintain. The thermostat, locatedin the conditioned (heated and/or cooled) space,senses room temperature, and when the room tem-

perature varies from your setpoint, the thermostatactivates the heating or cooling system.

A dual heating/cooling thermostat will have switch-es that let you change the system from heating tocooling and operate the fan separately. Some ther-mostats also allow you to turn off the heating andcooling systems.

All heating and cooling thermostats operate withsimilar buttons and controls. The basic and com-mon controls are as follows:

HEAT – OFF – COOL

This switch will put the system in the heating mode(HEAT), turn the system off (OFF), or switch the sys-tem to cooling (COOL) if there is an air condition-ing system. Once the system is set to HEAT orCOOL, the thermostat temperature setting controlsthe system based on the room temperature.

FAN – ON – AUTO

This switch allows operation of the fan manually(ON), independent of the heating and cooling sys-tem. This allows you to circulate air in your homewithout operating the heating or cooling system. Inthe automatic (AUTO) setting the fan will cycle onand off as needed by the heating or cooling sys-tem. AUTO is the setting normally used.

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How To Operate Your Home

Must Know / Must DoHeating and Air Conditioning

• Understand how your heating andcooling system works and who youcan call for service.

• Understand the control (thermostat)for the heating and cooling system.

• Perform basic maintenance: filterchanges and lubrication.

• Schedule yearly maintenance by aprofessional.

• Identify and know how to useemergency shutoffs for electricity,gas, oil, and so on.



The typical home system is either fully on or fullyoff; it doesn’t provide variable heating/cooling.When the thermostat calls for heat, the furnacereacts at 100 percent capacity until the room tem-perature reaches the setpoint; then the furnaceshuts off. Turning the thermostat up higher will notheat the room any faster. When you switch the sys-tem to cooling, turning the thermostat lower willnot cool the room any faster. (A few homes dohave complicated systems in which the furnace iscapable of variable heating/cooling, but these arethe exception.)

Electronic (or digital) thermostats can be pro-grammed for automatic adjustment of the setpointtemperature based on time of day and day ofweek. These help conserve energy; they can lowerthe temperature during sleeping hours or whenyour home is not occupied.

Thermostats should be installed and maintained byprofessionals. Special anticipator settings on thethermostat match its operation with the operationof the furnace. If you replace a thermostat, makesure that this anticipator setting is done properly.

Thermostats are very sensitive. Your thermostatshould be level, out of direct sunlight, and awayfrom direct heat sources. If a thermostat develops amajor problem, the usual recommendation isreplacement rather than repair, because much bet-ter electronic thermostats with modern setbackcapabilities are readily available at reasonable prices.

To obtain detailed information on thermostats, seethe References section; many manufacturers willsend instructions for a specific thermostat.

Warm Air Furnace

The most common type of warm air (forced air) fur-nace provides heat by burning a fossil fuel to warmair and then distributing the warm air inside yourhome. The heat source is confined within a heatexchanger inside the furnace housing. For gas,propane, and oil systems, the fuel is burned inside orbelow a heat exchanger. The hot products of com-bustion flow through the heat exchanger and up achimney or are drawn out through a vent pipe.

The hot products of combustion warm the metal ofthe heat exchanger. After a minute or so, when theheat exchanger’s metal is warm, the circulating (fur-nace) fan starts. This fan circulates air across the hotmetal on the outside of the heat exchanger. Theheated air warms your home.

For homes without basements or crawl spaces,warm air furnaces can be located in attics or closetspaces. The typical warm air furnace located in anattic or crawl space uses the same components as abasement (upflow type) furnace but the furnace isoften designed to operate horizontally to save space.

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Furnaces for homes built on a concrete slab arelocated in the attic or in a closet. For the closetinstallations, a downflow warm air furnace may beused. These furnaces are similar to the upflow fur-nace, but the components are reversed. The heatsupply ducts are in the floor slab. Homes on slabscan also have a warm air furnace in a closet usinga typical upflow furance – the supply ducts will bein the attic and the return will be through the hallsor in the floor slab.

The efficiency of gas furnaces has improved dramati-cally in recent years. Standard (60%) warm air fur-naces have been improved with electronic ignitiondevices to eliminate the standing pilot light and pre-vent this heat loss. These furnaces have also beenimproved with a motor-operated flue damper in thepipe that goes to the chimney. When the burner ison, the damper is open. When the burner is off, thedamper closes and eliminates the draft up the chim-ney, saving energy. These improvements will make a60% furnace operate at about 65 to 70% efficiency.

You will find 80% efficiency furnaces that use adraft fan to force the products of combustion upthe chimney. You will find 90%+ efficiency furnacesthat vent with plastic PVC pipe. These higher effi-ciency furnaces squeeze so much energy out of the

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products of combustion that they need special fansto help remove the products of combustion; thecombustion gas is not hot enough to naturally draftup the chimney.

In an electric warm air furnace, air circulates directlyover an electrical resistance-heating element.

A propane gas furnace is similar to a natural gasfurnace but uses a different burner and control sys-tem designed for propane.

Oil warm air furnaces have a special oil burner andcombustion chamber. The burner pressurizes the oiland sprays it through a small nozzle, forming amist. The burner also provides an air supply and ahigh-voltage spark. This results in a very hot flamethat is contained in a ceramic combustion chamber.From the combustion chamber, the hot combustiongas flows up through the heat exchanger, just as ina gas furnace.

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A warm air furnace recirculates air in your home. Itdoes not draw in outside air unless there are specialprovisions for an outside air supply (which is notcommon). The fan circulates the air, which is drawn

from the return grills and ducts inside your homeand discharged through the supply grills. There willbe a furnace air filter located near the fan; youmust maintain this filter.

Systems for air supply and ducting have changedthrough the years. The early “gravity” warm air fur-nace system (commonly called an octopus) did notuse a circulating fan. The air was said to move by“gravity”—that is, warm air simply rose up into therooms. This type of system often has warm supplygrills in the center of the home and the cold returnsalong outside walls.

When furnaces were improved with circulating fans(the forced air/warm air furnace), heating ductsmade a transition to the upper portion of the cen-ter wall; return ducts were still located along theouter walls. In an older home, you may find astrange combination of supply and return grills,since they were added as heating systems wereupgraded or replaced.

Warm air or forced air furnaces have a circulatingfan or blower located near the heat exchanger. This

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fan circulates the house air over the warm metal ofthe heat exchanger inside the furnace. The fan maybe powered directly by a fan motor mounted insidethe fan housing. A motor through a belt and pulleyarrangement may also power the fan.

For a belt drive fan, you must maintain the belt andbelt alignment. Turn off power to the unit beforeyou open the fan chamber. The belt should not becracked or frayed. If the belt is very hard and shinyon the driving “v” sides, it is old and needs to bereplaced. The pulleys should align so the belt runsstraight between each pulley.

Proper tension on the belt is required to transmitpower. With moderate hand pressure applied onthe belt one-half way between the pulleys, the beltshould deflect about 1/2 to 3/4 inch. The motormounting brackets are often adjustable to changethe belt tension.

Many older furnaces require lubrication of the bear-ings on the fan and fan motor. On newer furnaces,bearings may be lubricated for life and will notneed additional lubrication. Check your owner’smanual or consult with a heating contractor for thespecific requirements for your furnace. You can alsolook at the ends of the fan and the motor; you maysee little (1/4-inch) caps over little tubes. These are

ports in which to add oil for lubrication. Generallythese bearings should be lubricated with a fewdrops of light oil every few months.

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Newer furnaces will also have a safety switch builtinto the fan access door. When the fan chamberdoor is removed, this switch shuts the furnace off.This is a safety device that prevents accidental injuryfrom the moving part of the fan system. If you everhave a situation with no heat or no air condition-ing, you should check this access door and safetyswitch. A loose fan access door can inadvertentlyshut the system down.

An older home may also have a supply grill withouta return grill. This is common in the second story ofCape Cod style houses. Often this works well forheating but not for proper air conditioning.

With modern systems, heat ducts are located onthe floor or ceiling near the outside walls, windowsand doors. Returns are placed on interior walls. Ifthe furnace is in the basement or crawl space, sup-ply grills will be near the floor; if the furnace or sup-ply ducting is in the attic, supply grills will be in theceiling. This modern arrangement provides forgood air distribution and greater comfort. Mostmodern systems have a return grill in every roomexcept the bathrooms.

Air Filters

Air filters are provided on all forced air furnaces toremove dirt and lint from heated air.

This keeps the fan, heat exchanger and air condi-tioning coil clean. It also helps clean the air of yourhome as air circulates through the system (note thedirection of the air flow).

Media Filters

ONE-INCH-THICK FIBERGLASS

The standard filter on most furnaces is a nominal1”-thick media filter. Usually, this filter is made offiberglass. The filter should be changed when it isvisibly dirty—usually every month or two, depend-ing on the quality of the filter and the amount of

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dirt in your home’s air. Children, pets, plants, andactivity tend to produce more dirt that finds its wayinto the heating system.

Be careful about the direction of the air flowthrough the filter. Filters are designed to be installedwith one particular side facing the air stream. Mostfilters have directions or an arrow telling you whichside should be installed toward the furnace. Thearrow is the direction of the air flow and should betoward the base or the fan of the furnace.

Remember: the furnace filter is also used whenyou operate the fan and/or central air condition-ing, so you should check on the filter during thesummer, too.

PAPER

I recommend that you try one of the pleated paperfilters. These catch more dirt than inexpensive fiber-glass filters. Some even have a static charge toattract dirt. Others have a carbon filter content.Paper filters cost between $3 and $15 and can befound in most hardware stores. You will need tochange this type of filter more often because it col-lects more dirt.

WASHABLE

Washable filters can be made of foam or wovensynthetic fiber. They are about as effective as inex-pensive fiberglass filters. You can improve the effi-ciency of a foam filter by spraying it with a specialfilter coating; this oily/waxy spray helps the filterhold dirt better.

PLEATED, 4- TO 6-INCH THICK

A big improvement over the standard 1”-thick filteris a pleated fiberglass or paper filter.

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Must Know / Must DoRoutinely Maintain the Furnace Filter

Maintenance is based on the type offilter, how often the unit is running(heating and cooling), and how youuse your home. The three basic typesof filters are media, electronic, andelectrostatic.



Often, the pleated paper filter is housed in a 6”-thick frame. The paper filter is very fine, and itcatches smaller particles of dirt and dust. This typeof filter is normally changed once per year, and youreplace only the paper element.

A pleated fiberglass filter often is mounted in athrowaway paper frame. The entire unit is replacedabout once a year.

Electronic Filters

Electronic filters use electrically charged metal platesand wires that attract dirt. These filters can removevery small particles from smoke and pollen whicharen’t caught by standard filters. If you have respira-tory problems or are sensitive to dust or pollen, youmay want to use this type of filter.

Electronic filters cost more than $600 to install.Maintenance involves washing the interior frame andmetal plates and wires with detergent or runningthem through a dishwasher. Most electronic filtershave a metal pre-filter that also must be washed. For

more specific cleaning instructions, contact a heatingcontractor or the filter manufacturer. The Referencessection includes contact information.

Electrostatic and Electronic Filters

Many types of washable filters have multiple layersof filtering material; vendors claim these layers con-tain an electrostatic charge that attracts and trapsdirt more effectively than a standard media filter.

Several companies also make a 1”-thick electrostat-ic/electronic filter as a direct replacement for throw-away filters. This filter may have an electronicpower supply and may require particular mainte-nance procedures.

For more information on filters, look upmanufacturers in the References section.

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Warm Air Furnace—Maintenance Requirements

All heating equipment should be routinely checkedby a qualified service technician. Most furnace man-ufacturers recommend yearly maintenance.

ROUTINE MAINTENANCE A HOMEOWNERSHOULD PERFORM

Note: Turn off power to the unit before inspectionor maintenance.

• Maintain records. Have a professional servicethe unit yearly. Proper maintenance keepsequipment operating efficiently and ensuressafety. Contact the manufacturer of your fur-nace for specific maintenance requirements. Seethe References section for contact information.

• Change the filter as required—often every othermonth.

• Switch high/low returns at the start and end ofthe heating season. For complete instructions,check the section on “Heating and CoolingDistribution” later in this chapter.

• Check all flue pipes and vents for rust, waterleaks, and loose connections.

• Lubricate the fan motor and fan bearing with afew drops of oil twice per year. (This is onlyrequired on certain units.)

• Check the belt to make sure it’s not cracked orloose. (This is only required with belt-driven fans.)

• Listen to the furnace operate. Follow up on anystrange sounds.

• Check drain lines to make sure they are clearand draining properly.

• Look for water leaks or changes in the system.

ROUTINE MAINTENANCE A PROFESSIONALSHOULD PERFORM

During a routine service call, the service technicianshould perform the following general maintenancemeasures. The technician may perform otherchecks, too, depending on the type of furnace.

• Check and clean burner.

• Check flue pipes, draft diverter, heat exchanger,and chimney.

• Remove burners to clean burners and heatexchanger if necessary.

• Check electrical wiring and connections.

• Check and clean circulating fan. Lubricate fanand motor if necessary.

• For belt drive fans: check for tension, wear andalignment.

• Check supply and returns ducts for air leakage,water stains, rust.

• Check and maintain filter.

• Perform an operational check of furnace andsafety controls.

• Test for carbon monoxide in the flue gas and inthe air around the furnace.

• Check for gas leaks.

• Check, clean, and adjust pilot light if necessary.

For a high-efficiency furnace, the technician should also:

• Check for water leaks (condensation fromcombustion).

• Check flue pipes and connections.

• Check for condensation on metal pipes andparts.

• Check for a clean condensate drain line.

• Check operation and condition of draft fan.

Duplicates of the above lists appear in the ServiceChecklists chapter. You may want to make a photo-copy of the professional’s list and send it to the serv-ice company when you arrange service and/orreview the list with the technician at the beginningof the service call.

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Hydronic (Hot Water) Heat

Hot water or hydronic systems provide heat bywarming water and circulating it through piping toheating devices: radiators, baseboard convectors,radiant pipes in the floors or walls, or even coilswith a fan. Older system typically use cast iron radi-ators; newer systems typically use baseboard con-vectors (finned tubes).

Hydronic systems usually burn oil, gas, or propanebelow a cast iron container or coil that holds water.The warmed water is then distributed to the radia-tors through a network of supply and return pip-ing. Older systems use gravity to move the water—warm water rises, cool water falls. Newer systemsuse a small circulation pump to move the water.

The distribution system is sealed and should notleak, but water expands as it warms, so there willbe an expansion tank to hold the increased vol-ume. Most systems have an automated fill valveand backflow prevention.

The system automatically responds to a thermostatlocated in the heated space. When the thermostatcalls for heat, the boiler and the pump start. Warmwater is delivered to the radiators. When the ther-mostat is satisfied, the boiler is turned off.

There are many variations to hydronic systems: mul-tiple zones provided by thermostat and zone con-trol valves or multiple pumps…boiler temperaturewater resets based on outside temperature….manycontrol options…and variations in piping systems,to name a few. If you have a complicated system,ask a service technician to explain it to you.

Hydronic Heating—Maintenance Requirements

All heating equipment should be routinely checkedby a qualified service technician. Most hydronicboiler manufacturers recommend yearly mainte-nance to keep equipment operating efficiently andto ensure safety.

Contact the manufacturer of your furnace for spe-cific maintenance requirements. See the Referencessection for contacts.


Note: Turn off power to the unit before inspectionor maintenance.

• Maintain records, and have a professional serv-ice the unit yearly.

• Check all flue pipes and vents for rust, waterleaks, loose connections.

• Listen to the boiler operate. Follow up on anystrange noises.

• Check drain lines to make sure they are clearand draining properly. (This is required only forhigh efficiency condensing units.)


• Oil the circulating pump twice per year. (Usejust a few drops).

• Check that the temperature/pressure gauge isin the operating range identified by a profes-sional service technician. Mark the proper rangeon the gauge.

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A service technician should perform the followinggeneral maintenance measures. The service techni-cian may also perform additional checks, depend-ing on the type of furnace.

• Check and clean burner.

• Vent the system at the high points as necessary.

• Check all flue pipes, draft diverter, boiler hous-ing, and chimney.

• Remove burners to clean burners and heatexchanger if necessary.


• Check and lubricate circulating pump(s).

• Check for water leaks.

• Check temperature and pressure relief valve.

• Check water supply system and backflow preventer.

• Add backflow preventer if none is present.

• Check expansion tank for proper water level.

• Perform an operational check of controls fortemperature, pressure, and safety.

• Test for carbon monoxide in the flue gas and inthe air around the furnace.


• Check, clean, and (if necessary) adjust pilot light.

Additional checks for a high-efficiency boiler with adraft fan:

• Check draft fan for condensation and rust.

• Check flue pipe for condensation.

• Check condensate drain lines.

Duplicates of the above lists appear in theService Checklists chapter. You may want tomake a photocopy of the professional’s list andsend it to the service company when youarrange service and/or review the list with thetechnician at the beginning of the service call.

Steam Heating

A steam heating system is similar to a hydronic boil-er system except that it produces steam at low pres-sure. Because they require more maintenance thanhydronic systems, steam systems are rarely installedin newer homes, and older steam systems often areconverted to hydronic systems.

Steam systems can use oil, natural gas or propaneas an energy source. The burning fuel heats waterin the boiler, turning it to steam. The steam, underpressure, rises through the system to the radiators.Vents in the radiators release heated air. The steamcondenses back into water as it releases energy inthe radiator, and the water flows back to the boilerto be reheated.

While there are variations in the piping systems,almost all residential systems are “one-pipe” systemsas described above. You can identify a one-pipe sys-tem because it will have only one pipe connectedto the radiators.

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Steam systems should have professional maintenanceat least once per year, perhaps more often. Much ofthe maintenance required by a steam system is toocomplicated for most homeowners to perform.


• Maintain records.

• Check all flue pipes and vents for leaks, rust,and loose connections.

• Check the system for any leaks.

• Check the steam gauge. Have your contractormark the normal range.

• Check the water level every month. The normalrange should be marked on a sight glass.

• Make the sure the radiators slope slightlytoward the steam inlet pipe. This will help keepthe pipe from knocking or pounding.

• Make sure the vents on the radiators are operat-ing; otherwise, radiators may be cold.


A service technician should perform the followinggeneral maintenance measures. The service techni-cian may also perform additional checks, depend-ing on the type of boiler. (For a gas-fired system,see the information on oil burners, which requireadditional checks.)

• Check and clean the burner.

• Check all vents on radiators and piping.

• Check all flue pipes, draft diverter, boiler hous-ing and chimney.

• Remove burners to clean them and the heatexchanger if necessary.


• Check for water or steam leaks.

• Check the temperature and pressure relief valve.

• Add a backflow preventer if none is present.

• Perform an operational check of controls fortemperature, pressure and safety.

• Test for carbon monoxide in the flue gas andthe air around the boiler.


• Check, clean and if necessary adjust the pilot light.


Oil Burner

An oil burner can be used just like a gas burner inwarm air furnaces, hydronic systems or even waterheaters. All oil burners are essentially the sameexcept for some very old style vaporizing or pot-type burners. Here we will only cover modern pres-sure burners or gun-type burners.

A modern oil burner pressurizes oil and sprays itthrough a small nozzle, forming a mist. At the sametime, the burner provides an air supply and a high-voltage spark. This results in a very hot flame that iscontained in a ceramic combustion chamber. Fromthe combustion chamber, the hot combustion gasflows up through the heat exchanger, just as in agas-fired appliance.

Oil Heat—Maintenance Requirements

Oil burners can be quite efficient, comparable togas units. Oil burners require yearly maintenance.Also, never let your oil system run out of fuel. Thiscan cause major problems with the burner, requir-ing a service call.

Most homeowners find it convenient to arrange foran oil delivery and burner service company to pro-vide automatic oil tank filling and yearly service. Thisis the best way to ensure that the system is operatingproperly. You will also be placed at the top of theservice call list if you are an established customer.

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Note: Turn off power to the unit before attemptinginspection or maintenance.

• Follow the maintenance requirements listedabove for warm air or hydronic boiler systems.

• Schedule routine maintenance yearly.

• Lubricate the burner motor if it has oil ports (askyour service technician).

• Make sure the system never, never runs out offuel oil.


A service technician should perform the followinggeneral maintenance measures. The service techni-cian may also perform additional checks, depend-ing on the type of furnace.

• Follow applicable maintenance requirementslisted above for a hydronic boiler or warm airfurnace.

• Remove and clean burner, clean blower blades,replace or clean filter and/or strainer, replacethe nozzle, clean flame and heat sensors, checkand clean or replace electrodes.

• Lubricate the burner motor.

• Check flue and barometric damper.

• Check for oil leaks.

• Check and clean oil pump.

• Clean and test stack control.

• Check and adjust draft regulator.

• Test for efficiency and make proper adjustments.


Central Air Conditioning

Central air conditioning uses a warm air furnacesystem to cool air and distribute it throughout thehome. The air conditioning system uses the fan, fil-ter, thermostat and ducts; the heating portion ofthe system remains turned off.

When a home has hydronic heat, central air condi-tioning may be provided by a separate system. Inthis case, there is no heating equipment in thestandard furnace housing; it has only a fan andcooling coil.

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A central air system includes an interior coil (in thefurnace housing) that removes heat from the interi-or air and an exterior coil that rejects heat into airoutside the house.

When the thermostat signals for cooling, this starts upthe exterior refrigeration compressor, exterior fan andfurnace fan. The exterior compressor moves refriger-ant through the closed system of coils and valves toproduce a cool coil inside.The furnace fan moves airacross this coil. The air cools, and moisture condenseson the coil’s surface. This moisture is caught in a panbelow the coil and drains away through a hose.

It is not necessary to cover the exterior unit duringthe winter, since these units are designed to with-stand the weather. If you do cover the unit forsome reason (for instance, if the unit is locatedwhere debris might accumulate on it), it’s best tocover only the top of the unit. If you were tosecurely wrap the sides, moisture could condensein the unit. Also, a wrapped unit provides a perfectwinter home for animals that may chew wiring andcause other problems.

When it’s time for the winter shutdown, turn offpower to the unit to prevent accidental operation.The power disconnect could be the breaker or fuseat the main panel. Or the disconnect may be at theexterior unit, usually as a switch or a fuse block orplug that you pull out to disconnect the power.

Central air conditioning systems should neverbe operated in cold weather. This can causeserious damage.

Don’t start the central air conditioner unless theoutdoor temperature has been above 60 degreesfor at least 24 hours. Remember to uncover theunit if you added a cover for the winter.

At the start of the cooling season, when you’reabout to turn on power to the unit, make sure thatthe thermostat is switched off, and leave the ther-mostat off for 24 hours before operating the unit. Ifthe unit has a crankcase heater, this procedureallows the heater to warm the unit.

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Central Air Conditioning– Maintenance Requirements

Proper maintenance will keep the unit operatingproperly and save you energy costs. Have your airconditioning system checked yearly by a profession-al service contractor.

You should also perform basic maintenance.Contact the manufacturer of your furnace/AC unitfor specific maintenance requirements; see theReferences section for contact information.


Note: Turn off all power and disconnect switchesbefore performing inspections/maintenance.

• Maintain records, and have a professional serv-ice the unit yearly.

• Change the filter as often as required (in somecases, every month).

• Switch high/low returns (and adjust ductwork ifnecessary) at the start and end of the coolingseason. For complete instructions, check thesection on “Heating and Cooling Distribution”later in this chapter.

• Listen to the air conditioner operate. Follow upon any strange noises.

• Check drain lines from the furnace to make surethey are clear and draining properly.


• Keep plants and obstructions away from theexterior coil and fan. Allow 3 feet of clearance atthe air discharge and 1 foot all around the unit.

• Keep the exterior coil clean.

• Keep the exterior unit level and away from soilor landscape materials.

• Make sure that supply and return registersinside your home are not blocked.

FALL MAINTENANCE

1. Disconnect power to the unit to prevent acci-dental use.

2. (Optional)—Cover the top of the unit.

SPRING MAINTENANCE

1. Uncover the unit.

2. Turn the power on 24 hours before operation.Keep the thermostat off.

3. Perform the maintenance listed above and arrange for professional service.

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A service technician should perform the followingprocedures during a routine service call. The techni-cian may perform additional checks, depending onthe type of air conditioner you have.

• Check filter and replace as needed.

• Check exterior unit for level conditions, a cleancoil, clearances, and adequate air flow.

• Check interior temperature drop across the cool-ing coil (15 to 22 degrees F).

• Check the condensate drain pan and line.

• Check secondary pan and line if unit is locatedin an attic.

• Look for signs of water leaks or excessive airleaks.

• Lubricate the fan motor and check the belt ifrequired.

• Inspect electrical connections.

• Inspect refrigerant lines for signs of leaks.

• If performance problems exist, the technician-may check for amp draw, clean the coils, checkthe refrigerant charge, and/or complete generalperformance tests.


Central Air Cooling – Evaporative Cooler

Evaporative coolers, commonly called “swamp cool-ers,” are used for cooling in climates where air tem-peratures are high and relative humidity is very low.The outside air must be hot and dry for the units tofunction, so they are only used in hot, arid placeslike the American Southwest. This type of coolingwill not work in humid climates.

The evaporative cooler works because hot outsideair can be cooled as it absorbs moisture. As hot out-side air is drawn across a pad full of water, thewater evaporates into the air and the air is cooledas much as 20 degrees. The energy required tochange the water into invisible vapor in the airmakes the temperature drop.

In the process, the air is also humidified, butbecause it was so dry to begin with, this additionalmoisture is not objectionable. The cooled air is cir-culated through the home and to the outdoors.

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The evaporative cooler is typically located on theroof; cooled air is ducted into rooms and out thewindows. A cooler can also be mounted in a win-dow or on a concrete pad outside the home.

Evaporative cooling is what cools our bodies in hotclimates. As sweat evaporates, it takes heat fromour skin. We can speed the cooling process by wet-ting our skin with a water mist and blowing airacross our skin. That is why we feel cooler whenwe leave a swimming pool and the wind is blow-ing—we are experiencing evaporative cooling.

The basic evaporative cooler operates as fol-lows:

1. A water pan on the unit is automatically filledby a float, fill valve, and water supply.

2. A small pump in the pan lifts water and distrib-utes it over evaporative pads on the sides of theunit. The excess water drains back into the pan.

3. A large fan draws hot, dry exterior air across thesaturated pads.

4. As dry air is drawn across the wet pads, it gainsmoisture and is cooled. The energy needed tochange water into vapor cools the air.

5. The cooler air is pushed into the home and outthe windows.

6. In the process, humidity is added to interior air.

7. Since the pads filter the air and trap particles,the systems may flush out deposits through adrain line in the bottom of the water pan.

Evaporative coolers are less expensive to install andoperate than refrigerant-based central air condition-ing systems, but they must be maintained, and leaksmust be prevented to limit any damage to a home.

Evaporative Cooler – Maintenance Requirements

Proper maintenance will keep the unit operatingproperly and prevent water leaks and contamination.Because the pads filter outside air, pad and pansmust be maintained. Specific maintenance require-ments for homeowners and for professional serviceare in Chapter 23: Service Checklists.

Heat Pumps

A heat pump provides heating and cooling. Simplyput, a heat pump is a central air conditioner thatcan cycle in reverse to provide heating.

Local conditions will dictate whether a heat pumpis an efficient alternative for heating your home.

A heat pump transfers heat from an exterior coil toan interior coil in the warm air heating system. Aheat pump provides efficient heating in areas whereexterior temperatures are moderate. In cold winterweather, though, a heat pump is no more efficientthan electrical resistance heating, which costs moreto operate than a natural gas or oil furnace.

Before you use your heat pump, have a profes-sional explain its operation. Unfortunately, it’s easyto accidentally operate the system with emer-gency electrical heat; in this mode, the heat pumpis turned off and electrical resistance heating coilsturn on. This method works fine, and you maynot observe any problems—until you get yourelectric bill.

The emergency (electrical resistance) system shouldonly be used when (1) the heat pump is not work-ing, or (2) the outside temperature is so cold (about30 degrees or lower) that the heat pump would be

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less efficient than electric resistance heating. Whenthe outside temperature gets this low, emergencyresistance heating turns on automatically. You donot need to adjust the controls.

Heat Pump—Maintenance Requirements

Maintenance for a heat pump is similar to that forcentral air conditioning systems, but because a heatpump is operated winter and summer, it will requiremore maintenance.


Note: Turn off all power and disconnect switchesbefore performing inspections/maintenance.

• Schedule professional service yearly.

• Watch for ice forming on the exterior unit. Thisis a serious problem indicating that the unitneeds service.

• Follow all the maintenance recommendationsfor central air conditioning.


A service technician should perform the followingprocedures during a routine service call. The techni-cian may perform additional checks, depending onthe type of heat pump you have.

• Follow all maintenance requirements for centralair conditioning.

• Follow specific recommendations by the heatpump manufacturer.

• Check filter and replace as needed.

• Check exterior unit for level conditions, a cleancoil, clearances, and adequate air flow.

• Check interior temperature drop across the cool-ing coil (15 to 22 degrees F).

• Check the condensate drain pan and line.

• Check secondary pan and line if unit is locatedin an attic.

• Look for signs of water leaks or excessive air leaks.

• Lubricate the fan motor and check the belt ifrequired.

• Inspect electrical connections.

• Inspect refrigerant lines for signs of leaks.

• If performance problems exist, the technicianmay check for amp draw, clean the coils, checkthe refrigerant charge, and/or complete generalperformance tests.

• Follow any specific recommendations by theheat pump manufacturer.


Heating and Cooling Distribution:Ducts and Dampers

Warm air heating (and central air conditioning) is dis-tributed throughout your home by a system of ducts,dampers and grills. Supply grills provide conditionedair, and return grills provide a route for the air toreturn to the central heating/cooling unit. The centralfan circulates air through these ducts and grills.

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These ducts may be metal, fiberglass or even flexi-ble plastic. When there is a basement or crawlspace, the ducts are often located just below thefirst floor. When the furnace is in the attic, distribu-tion is routed through the attic. Often, framing injoist or stud spaces forms return ducts. For homeswith slab foundations, the ducts may be buried inthe foundation slab.

In warmer climates, for homes with slab construc-tion, the furnace is often located in the attachedgarage with supply ductwork in the attic and areturn in the central hall.

This distribution system often has adjustabledampers that control the air flow to certain pointsin your home. Frequently, these dampers areadjusted during installation and are never re-adjust-ed later. At times, though, dampers should beadjusted when switching from heating to coolingor to accommodate a central humidifier that isturned on in winter and off in the summer.

For a two-story home, you may need to make airflow adjustments for winter and summer. In thewinter, warm air rises to the second floor, and youdon’t need as much heating up there. In the sum-mer, warm air still rises, and the hot attic adds moreheat, so you’ll need more cooling (air flow) to thesecond floor than the first.

Dampers are located inside the ducting system.Often, you’ll find dampers where round supplyducts connect to the main rectangular ducts. Allyou will see of a damper is a small lever and lock

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Must Know / Must DoDuctwork and Dampers

• Never allow openings or holes inductwork. This wastes energy andmakes living spaces uncomfortable.

• You may need to adjust ductworkdampers when switching fromheating to cooling or vice versa.

• If your furnace has a damper onthe humidifier, you may need toadjust it. Turn it off during summer.

• Ask your service technician if yourwarm air furnace has a damper fora winter/summer switch.

• Ductwork in attics and crawl spacesshould be well insulated to preventloss of energy.



nut or a small shaft and a wing nut. You can deter-mine the position of the damper by checking thedirection of the lever or the screwdriver slot in theend of the shaft. If the lever or slot is parallel to theduct, this means the damper is open. If thelever/slot is perpendicular (at a right angle) to theduct, the damper is closed. Some systems havelevers indicating the direction of the damper. Somerectangular ducts have dampers and levers. Youcan adjust these dampers to close off rooms youdon’t want to heat/cool or to provide more heatingor cooling to specific rooms.

At the start of hot summer weather, you may needto direct more cool air to the second story. Start byfully opening all second-floor dampers. Next, par-tially close dampers to first floor rooms that are coldand receiving lots of air. The dampers often fitloosely in the ducts, so you may find that closingthe damper 50% (turning the shaft 45 degrees) willonly partially slow the air flow. Sometimes air willflow through a fully closed damper.

However, don’t close off more than one-quarter of allthe dampers; operation can be hindered if too littleair flows through the system. If you need to makemajor changes to the system, consult a professional.

Once you’ve found a desirable balance, mark thedamper settings for winter and summer.

High and Low Returns

Some distribution systems have “high” and “low”return grills on interior walls. These grills are locatedone above the other. They aid in air distributionand comfort.

High returns should be opened for cooling.Remember that warm air rises, and you want toreturn the warm air to the air conditioning coil inthe furnace.

During the heating season, the low returns should beopen to return cold air at floor level to the furnace.

Outside Air Supply

Since the mid 1990s, the concept of adding an out-side air supply to a forced air duct system hasbecome more popular and has been required bysome code officials. This involves installing a ductbetween the home’s exterior and the return ducton the forced air system. When the furnace fanoperates, it draws a small amount of air from theoutside. This outside air duct may have a damperthat can be closed in the summer when the unit isused as an air conditioner. The duct is usually insu-lated to prevent condensation on a cold surface inthe winter.

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The goal of the outside air supply duct is to providesome ventilation air. Since this air is cold and dryduring the heating season, it will help dry thehome’s interior air. As air is introduced into the sys-tem, an equal amount of warm damp air leaks outof the home. This also tends to remove moisturefrom the home.

Humidifier Controls and Settings

In northern heating climates, homes can becomevery dry in the winter. As warm air leaks out of ourhomes, it is replaced with cold, dry air. This is lesssevere if we have tightened up our homes for ener-gy conservation, but it still can be a problem.

Excessive dryness can damage furniture and harmyour physical well-being.

The simple way to add moisture to the air of yourhome is with a central humidifier on your warm airfurnace. A modern system is easy to maintain andshould not leak. Modern systems have automaticcontrols that sense humidity level and operateautomatically.

Older systems are not the best, but some are serv-iceable. Do not use the type that employs a waterpan with an automatic fill valve. These are hard tomaintain, may harbor disease-causing bacteria, andcan leak water and ruin a furnace by rusting it out.

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The type with a water panel and drain (Aprilaire is acommon brand) works well if you maintain it. Thissystem slowly flushes water across a perforatedmetal panel, where the air picks up moisture.Excessive water drains through a pan and hose. Ingeneral, maintenance requires changing the waterpanel yearly and cleaning the pan and drain lines.Routinely check for water leaks, and keep the drainline clear.

You must also adjust the humidistat to compensatefor the outside air temperature. The humidistatlooks like a thermostat and is located next to thethermostat or on the ductwork of the furnace. Thecolder the outside temperature, the lower the interi-or humidity level should be. Your windows providea great humidity indicator. If moisture condenses onthe windows, the interior humidity level is too high.

Aprilaire offers a humidistat that automatically com-pensates for outside air temperature.

For more specific information, see the con-tacts listed in the References section.

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Must Know / Must DoCentral Humidifier

• Routinely check for leaks in thehumidifier. Leaks will ruin the fur-nace.

• Routinely clean and service the unitto prevent bacteria that endangerthe health of those in your home.

• Check that the drain line is clearand draining.

• Turn off the unit and its water sup-ply in the summer.

• Adjust the duct damper on the unitif necessary: off for summer, on forwinter.

• If condensation forms on your win-dows in the winter, lower thehumidity setting.

• Newer, tighter homes rarely need ahumidifier.



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Chapter 3 – Utility Systems – Heating and Air Conditioning · · 2018-01-27stand the basics of heating and air conditioning so ... Thermostat The thermostat ... This allows