Good ventilationis importantWhether you’re buying a new home or taking care of the oneyou’re in now, good ventilation is important because it helps pro-tect your health and your home. Good ventilation is as critical toyour comfort and safety as a reliable heating system, a smokealarm, or a dry basement.

Your health Good ventilation protects you, your family, and your guests fromunpleasant odors, irritating pollutants, and potentially dangerousgases like carbon monoxide and radon. Well-planned ventilationalso prevents the growth of mold and mildew, which can cause oraggravate allergic reactions and lung problems such as asthma.

Your home Good ventilation protects your home from damage by eliminatingexcess moisture from the air. Too much moisture rots window sillsand attic eaves, peels paint, and invites insect infestation. Dampinsulation in walls and ceilings means lost heat, higher fuel bills,and destructive mold growth. Carpeting, wallpaper, electronicequipment, and furniture all can be damaged by excess moisture.

Because people spendabout 90% of their timeinside, indoor air pollutioncan actually be a biggerhealth risk than pollution in the air outside, even incrowded cities and industrial areas.

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This booklet will introduce you tothe basics of home ventilation.Once you understand them,you’ll know why ventilation isimportant, how your home isventilated, and what you can doto improve it.

Ventilation means fresh air Ventilation supplies fresh air to your home and dilutes or removesstale air. There are many ways this can happen. For example,opening windows to air out your home can supply fresh outdoorair that dilutes stale indoor air. Turning on the fan over thekitchen range or in the bathroom removes odors and moisture.Other common examples of home ventilation include chimneys,which remove combustion gases, and clothes dryer fans, whichexhaust warm, moist air and chemicals from laundry soaps.

You may already know if you have a ventilation problem. Do younotice the sour smell of garbage from a trash can; a musty, gym-like smell coming from the bedroom walls; or mold or mildew inclosets, or on ceilings or exterior walls? Is there condensation onthe inside of your windows? Are your eyes irritated when you’reat home? These conditions may be signs of poor ventilation.

Fixing your home’s ventilationWhile just opening a window may seem like an easy, low-cost wayto provide fresh air, you will need a fan to make sure this air goeswhere it is needed. Good ventilation can be achieved at a reason-able cost. Depending on your home’s design and location and thetype of system you select, a ventilation system may cost in therange of $500 to $1,500, including installation. The cost to operatea typical ventilation system will be approximately $100 to $200 peryear, depending on your home’s location, the type of system used,and how your home was built. With new construction, operatingcosts can be minimized by building a well-insulated, tightly sealedhome with a well-designed ventilation system. These same featuresin existing homes can reduce operating costs because many homesare leakier than they need to be. Some ventilation systems includeenergy-recovery features. While more expensive to install, in timethey can pay for themselves in energy savings.

When gas and oil werecheap, most people didn’tpay attention to how leakytheir homes were; they justturned the thermostat upin the winter and down inthe summer. Buildingsoften had 3 to 5 timesmore ventilation than theyneeded. With rising pricesthat resulted from the1970s oil crises, peoplelooked for ways to reducethe cost of heating andcooling their homes. Thebuilding industry respondedby developing and installingmeasures such as betterwindows, more insulation,high-efficiency furnacesand air conditioners, andlimiting the amount of out-door air leaking into homes.Many of the problems dis-cussed in this guide soonbegan to appear. Although“tight” homes were part ofthe problem, they were alsopart of the solution. Well-sealed homes are less expensive to heat andventilate because you cancontrol how much outdoorair comes in and where it goes. The answer, then, is to “build tight and ventilate right.”

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VentilationbasicsThere are two basic approaches to ventilating your home:

❐ Spot ventilation for localized pollution sources

❐ General ventilation to dilute pollutants from sources thatexist in many locations or move from place to place.

General ventilation can be provided in two ways: exhaust-only, and supply-and-exhaust.

Whichever method you choose, spot ventilation is alsoneeded in those places where strong sources are located,such as bathrooms and kitchens.

Spot ventilation Spot ventilation uses exhaust fans to collect and remove pollutantsbefore they spread throughout your home. The exhaust fan is gen-erally turned on only when the source is producing pollutants.Bathrooms, kitchens, and laundry rooms all contain obvioussources of moisture and odors. Spot ventilation may also beappropriate for home offices, hobby rooms, or workshops.

Remember: every pol-lutant has a source.It may be as simpleas an overflowinggarbage can or ascomplicated as moldgrowing inside walls.Whatever the case,you must identify thesource before youcan solve the prob-lem. One of the easi-est ways to improveindoor air quality isto remove or avoidusing commonsources of moisture,odors, and gases.Some examplesinclude: not storingfirewood in the house,taking out thegarbage and thenwashing the can, andusing milder cleanersor water-basedpaints to avoidchemical odors.Although only a tem-porary solution,cleaning surface moldand mildew freshensthe air. Be aware,however, that somemolds can be danger-ous when released.

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When the pressure inside your home is lowerthan it is outside, the house is under negativepressure. In this case, outdoor air, includingthat in the soil, moves into the house.

When there is no difference between theindoor and outdoor pressure, the house is under neutral pressure. Air pressuredifferences also control the way air movesfrom room to room inside your home.

Air moves into, out of, and around the inside ofyour home because of differences in air pressure.

General ventilationGeneral ventilation fans run allthe time to control pollutantsfrom sources that can’t be spot-ventilated. For example, peopleand pets constantly release flakesof skin, bacteria, viruses, mois-ture, body odors, and digestivegases. Some sources, includingcarpets, furniture, and drapes, allof which release fabric fibers andgases such as formaldehyde, aretoo large or spread out to be spot-ventilated.

General ventilation mixes freshoutdoor air with stale indoor airto lower the concentration of pol-lutants (dilution). Fresh air isprovided by fans blowing out-door air into the house, whichforces air out through cracks andopenings (pressurizing), or byexhausting air from the house,which then draws fresh air inside(depressurizing).

Exhaust-onlyWith exhaust-only ventilation,exhaust fans pull stale air out ofyour home while drawing freshair in through cracks, windows,or fresh air intakes. If you usethis strategy, your home will bedepressurized. Exhaust-only ven-tilation is a good choice forhomes that do not have existingductwork to distribute heated orcooled air. However, if there isradon in the soil around thehouse, this method can increaseindoor radon levels. (See “radon”section on page 7.)

Supply-and-exhaustWith supply-and-exhaust ventila-tion, exhaust fans pull stale airout of the house while intakefans blow in fresh air. This sys-tem is more complex thanexhaust-only, but may ensure thebest flow of fresh air into yourhome. Outdoor air is drawn in byfans and delivered to roomsthrough heating and coolingducts. Supply-and-exhaust venti-lation is a good choice for homeswith heating or cooling ductsbecause it’s an inexpensive wayof providing fresh air. Somehomes may benefit from energy-recovery ventilation, whichwarms (or cools) incoming airwith outgoing exhaust air.

Air pressure differences are caused by such thingsas wind, temperature differences, and fans. Forexample, air moves into a home on the upwind sideand out of a home on the downwind side because ofpressure differences; heated air from a boiler or fire-place goes up a chimney because of temperaturedifferences; exhaust fans remove cooking odors bymaking the pressure in the kitchen lower than theair pressure outside. Air always moves from higher-to lower-pressure areas. Understanding how airmoves inside your home can help you avoid or fixsuch ventilation-related problems as excess mois-ture, backdrafting, and radon.

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If the pressure inside is higher than outside,your home is under positive pressure, andair moves out of the house.

Moisture problems occur whenwarm, moist air hits cold sur-faces, such as walls, windows,attic ceilings, air-conditioningducts, and plumbing. For thisreason, it can be helpful tokeep the pressure in yourhouse slightly negative in theheating season, pulling dryoutdoor air through the out-side walls into your home.When your home is air condi-tioned, it is better to keepthe pressure slightly positive,pushing dry indoor air intothe outside walls.

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Note:

There are certain circumstances when operating a house under negative pressure can cause serious problemsfor your family:

BackdraftingFurnaces, hot water heaters, and fireplaces need air to burn fueland exhaust combustion gases up the chimney. A house underenough negative pressure can pull air down the chimney, drawingcombustion gases such as carbon monoxide into the house. Thisis called “backdrafting” and is a very serious condition that canquickly cause severe injury or even death. Before installing a ven-tilation system, you should have your home checked to make surethere is adequate make-up air for the fuel-burning equipment.After the system has been installed, or after any major structuralchanges have been made, it is very important to recheck for bothbackdrafting and radon. (See “Selecting a contractor” section onpage 10.)

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RadonWhen a house is under negative pressure, it draws outdoor air from wherever itcan. Up to 20% of this “make-up” air comes from the ground, which can causeproblems if there is radon nearby. Radon is a radioactive gas found in soil, rock,and water that enters homes through cracks and holes in the foundation floorsand walls. According to the U.S. Environmental Protection Agency (EPA), long-term exposure to elevated levels of radon causes between 7,000 and 30,000 lungcancer deaths each year. The only way to know whether your home has a radonproblem is to test it. Your state radon contact or EPA can provide you with freeinformation on radon, including lists of people trained to test and fix homes withelevated radon levels. (See “For more information” section on page 11.)

Looking atyour home❐ Do you have both continuous general ventilation and

as-needed spot ventilation?

❐ Is your home free of lingering odors?

❐ Are your windows free of condensation?

❐ Is the dryer vented to the outdoors?

❐ Is each fuel-burning device, such as the woodstove, furnace,and hot water heater, vented separately?

❐ Are the exhaust ducts in unheated spaces insulated?

❐ Is the exhaust fan over the kitchen stove vented to the outdoors?

❐ Is there an exhaust fan in each bathroom?

❐ Has your home been tested for radon? If so, were the radonlevels high?

❐ Are outdoor air inlets located away from pollutant sources?

❐ Is each exhaust fan working and vented to the outdoors (notto the attic, soffit, or crawlspace)?

❐ Is exhaust air condensation-free?

Here are some questionsto help you evaluate yourhome’s ventilation system.If you answer “no” to anyof these questions, youshould consider makingsome changes.

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FRESHAIR

INTAKE

➡

Test #1From six inches away, squeeze a cloud of babypowder from its container toward the intake grilleof an operating exhaust fan. If the fan is workingproperly, the powder should be drawn into thegrille. If it goes to the center of the grille and isblown back into the room, then the fan isblocked; if the powder simply hangs in the air, thefan is not working.

Test #2Find a cardboard box with an opening big enoughto fit over the exhaust fan grille. If the fan ismounted in the wall, cut a hole slightly smallerthan a credit card in the bottom of the box, or, ifthe fan is mounted on the ceiling, in the side ofthe box. Using any kind of tape, attach a creditcard inside the box over the hole. Make sure thecard can swing back and forth in the box. Turnthe fan on and put the box over the exhaust grille.If the fan is working, the credit card will swinginto the box. The greater the air flow, the morethe credit card will swing open. If it swings open 11⁄2 inches or more, the fan is moving at least 25cubic feet of air per minute, which is a reasonableamount for a bathroom. If the card swings openless than 11⁄2 inches, you should consider repairingor replacing the exhaust fan. (Tip: use a pencilinstead of a ruler to measure how far the cardswings open, because a ruler will block the airflow.)

You can check the air flowthrough exhaust fans withthese two tests. The firsttells if your fan is working;the second tells how wellit’s working.

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Checking your exhaust fans

Selecting acontractorWhether designing a new home or improving the ventilation inyour existing home, you will probably need the services of anexperienced contractor. If you need information or help with thecombustion equipment in the house, the most knowledgeable people are gas utility technicians, heating contractors, and homeinspection professionals. If you need to know how the combustionequipment in your home affects other equipment and the houseitself, the people to talk to are usually weatherization contractors,home inspection professionals, or EPA-listed radon mitigation contractors.

As always, when hiring a building contractor, be sure to get acomplete cost estimate for the time and work involved. Youshould also get guarantees about the quality of work and materi-als, and assurance that you can transfer the guarantees to a newowner. Finally, the contractor should provide proof of liabilityinsurance.

When you talk to contractors, it’s importantto determine how well theyunderstand ventilationbasics and systems. Hereare some questions to askthem:

❐ What kind of ventilation train-ing do you have?

❐ What courses have you taken?

❐ Who provided the training andare they reputable?

❐ Who are your references?

❐ Do you have any photographsto show me of ventilationsystems you’ve installed?

❐ What tests will you perform todetermine problems with thecurrent equipment and thebuilding itself?

❐ What will the new systeminvolve?

❐ How long will it take you toinstall the system?

❐ Exactly how will it work?

❐ How will my heating/coolingbills be affected?

❐ How much maintenance willthis system require?

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