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Improving Your Indoor Air

By HHI Staff

It’s a rare house these days whose indoor air is so pristine that no measures are necessary to improve its quality. The sad truth is that most houses could use some help at cleaning up the indoor air. So, this section will offer some approaches you can take to make your home’s interior atmosphere healthier.


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A wide range of strategies are touted in the marketplace today to purify or clean the air—and they have an equally wide range of effectiveness. In the following sections, both strategies and effectiveness will discussed.

Simple Indoor Air Improvement Methods

Of course, good ventilation (the exchanging of stale indoor air for fresh outdoor air) and routine house cleaning are very important, and should help prevent or eliminate many household odors and pollutants. However, extra measures may be necessary from time to time. In certain cases, simple, inexpensive, non-mechanical solutions may be all that’s necessary.

Popular Odor Control Measures

The following methods are popular ones that people use to control odors in their homes. The best choices are those that are the least toxic, least persistently odorous in their own right, and the most effective at removing the original objectionable odor.

Activated Charcoal
Sometimes, a pie pan filled with activated charcoal helps eliminate odors within a small, confined space. Activated charcoal (made from coconut husks, as well as other substances) works because it has a tremendous capacity to adsorb. This means that odor molecules (from tobacco smoke, metabolic products of bacteria, as well as many compounds given off by plastics and other synthetic materials) quickly interact with, and adhere, to the many surfaces of the activated charcoal granules.

If you choose to use a pan of activated charcoal, place it so it can’t be easily tipped. You’ll also need to replace the activated charcoal occasionally when you find it isn’t adsorbing any more. Activated charcoal is available from many other manufacturers of air filters. It’s also often sold in pet shops and pet-supply centers because of its use in aquarium filters.
Active-Enzyme and Citrus-Based Deodorizers
One of the newest methods to eliminate, not to cover up, odors is with active enzymes. These are produced by benign bacterial cultures. The enzymes allow certain types of organic gases to be broken down so they can be ingested as food for the bacteria.

Another natural option is to deodorize with citrus compounds. These solvents have the ability to break-down certain odor molecules.
Aerosol Deodorizers and Disinfectants
Many typical deodorizing sprays are little more than diluted, aerated, synthetic fragrances. However, those labeled as disinfectants usually have, in addition, chemicals capable of inhibiting or killing certain biological contaminants, especially bacteria and mold.

Of course, the ingredients of these spray products are usually absorbed by your walls, floors, and furnishings—and you yourself, if you inhale them. Therefore, it may be best to avoid deodorizing and disinfecting sprays, especially if you’re an asthmatic or sensitive person. It should be remembered that some of the odors created by these sprays can be very long-lasting.
Baking Soda and Borax
Often, a safe solution to odors in small, confined spaces is simply to use an open box of baking soda. Of course, this has been done for years in refrigerators, but it can also reduce odors in your freezer and in closets. Baking soda is effective at eliminating odors because it’s able to absorb them. However, be sure it doesn’t get spilled, and remember to replace it from time to time.
Of course sprinkling baking soda on carpeting can help to reduce odors originating from the carpet fibers. You can use ordinary baking soda, or the type formulated especially for this job. However, if you choose a baking-soda carpet deodorizer, it’s best not to use one that’s scented. Whatever type of baking soda you choose, allow time for it to do its job, then vacuum thoroughly. Finally, a box of baking soda can be poured into the bottom of your cat’s litter box to reduce odors there. If you want to learn more deodorizing uses for baking soda, you’ll want to read Baking Soda: Over 500 Fabulous, Fun and Frugal Uses You’ve Probably Never Thought Of by Vicki Lansky. This may be available from your local library or favorite bookseller.

Another simple odor eliminator is to use a small amount of unscented borax in a bowl. As with baking soda used in this manner, it can absorb odors to freshen a small space. Again, be careful not to tip it over, and remember to replace it occasionally. Note: It’s important that borax not be ingested, so make certain that small children and pets can’t get access to it. Also, never sprinkle borax on carpeting. It’s granular texture may cut into carpet fibers.
Fabric Softener Sheets
A new household tip these days is to use fabric-softener dryer sheets as air fresheners. This use is now promoted through manufacturer’s advertising, and by household-hint “experts” as a wonderful, and simple, way to freshen up your home. So, placing scented dryer sheets under your area rugs, in your clothing drawers, and on closet shelves are all suggested.

Fabric-softener dryer sheets are typically non-woven pieces of rayon that are saturated with surfactants (compounds able to lessen water’s surface tension), and synthetic perfume. In truth, all they can do is contaminate your home with their own pervasive, odiferous compounds. They will not freshen anything. If you need to freshen your home, air it out and clean it, or rely on a really useful, safe, absorbent or adsorbing product.


One very popular odor-control method is to use potpourri. While some potpourri consists of natural dried herbs, spices, and flower petals, others also have added perfumes, either natural (as essential oils) or synthetic. However, no matter what is in them, potpourri can only mask unpleasant odors—not eliminate them. Then, too, potpourri’s own fragrant emanations can actually be more bothersome to certain sensitive individuals than the original unpleasant odors they were meant to disguise.


If you still want to use potpourri, consider only the all-natural types, to avoid breathing synthetic chemicals, and use only a minimal amount. Because the odors will permeate and linger, place potpourri only in areas where its odor won’t be bothersome for an extended period of time. To purchase potpourri, check in department and health-food stores. Other places to check are craft stores. In addition, your local library and bookstore will likely have books on how to make your own.

Scented Candles
Scented candles have really become popular, to not only add “a certain ambiance,” but to cover up less-than-pleasant room odors. However, simply put, they are not a healthy odor-control solution.

Of course scented candles, when lit, give off smoke and combustion gases, both of which can be unhealthy, and can cause respiratory inflammation. Research has also revealed that burning scented candles produces noxious volatile organic compounds (VOCs) such as acetone, benzene, and xylene. Still other compounds that are released include carbon dioxide and lead. Surprisingly, lead is used in many candle wicks! To top if off, the fragrances (usually synthetic) in these candles only act as a cover up, so odor molecules aren’t eliminated. In the end, candles simply add more pollution to your home.
Because many of the synthetic fragrances used in candles aren’t particularly combustible, burning scented candles results in incomplete combustion, and the release greater amounts of microscopic soot particles than unscented candles. As a result, burning very many of them indoors has caused thousands of dollars in soot damage in houses. When this type of damage first started appearing in homes, it was blamed on the furnace, or on chimney problems, but it has now been shown to be the result of burning candles. Of course, soot can certainly be caused by furnace or chimney problems, but whatever the source, soot isn’t healthy for people to breathe.

Solid, Stick-Up, and Plug-In Deodorizers

Solid, stick-up, and plug-in deodorizers have become the rage in recent years, especially the plug-in types. They are generally composed of nothing more than a synthetic scent in a gel, wax, or some other solid or semi-solid base (or perhaps in an imbedding pad). All are supposed to “freshen the air” continually. Therefore, the synthetic perfumes are always wafting about, as are the solid or semi-solid base ingredients. It should be noted that some people find plug-in air fresheners particularly bothersome. That’s because they’re designed to warm up to increase their ability to volatilize (evaporate into the air) their chemicals.

Interestingly, Anderson Laboratories, Inc. of West Hartford, VT decided to research the healthfulness of these types of deodorizers by exposing mice to one popular type. Their report, “The Toxic Effects of Air Freshener Emissions” (Archives of Environmental Health, 1997, Vol. 52, #6), found that acute respiratory and neurological effects (abnormal gait, reflexes, balance, and athletic performance) were experienced by mice as a result of exposure to the complex mixture of chemicals emitted by the air freshener. Using information garnered from manufacturer’s literature, this independent research lab concluded that some people, too, could experience eye, nose, and throat irritation, respiratory difficulties (such as asthma-like symptoms), and neurological effects (fatigue, confusion, dizziness) when exposed to this air freshener.

By the way, Anderson Laboratories, Inc. has actually “evaluated several air fresheners and found each of the ones we tested produced several forms of toxicity, especially to the eyes, nose, throat, lungs and nervous systems.” It was further discovered that certain air freshening products contain para-dichlorobenzene, a known carcinogen. If you’re interested in booklets, video tapes and copies of published papers concerning this air freshener research, the lab has them available for sale.
Obviously, scented, stick-up, and plug-in deodorizers are not recommended for healthy households. If you want to use something, consider using more benign materials such as baking soda, borax, zeolite, etc.
Zeolite is the name of a family of naturally occurring minerals. As with activated charcoal, zeolite works by the process of adsorption. Pollutant molecules are able to cling to its surfaces through what’s called the electrostatic force. (Electrostatic force causes like-charged molecules to repel and those with unlike charges to attract.) A real advantage to using zeolite is that it can often be renewed and reused many times, if it’s in granular or chunk form. Once the contaminated surface is no longer capable of adsorbing pollutants, the zeolite can be placed in the sun and, after a day or two, many of the adsorbed odors and gases will be released and dissipated into the outdoor air, thus reactivating the zeolite surface.


It must be noted that zeolite doesn’t work on every airborne pollutant (although it seems to work fairly well with formaldehyde and ammonia compounds), and different individuals have reported varying success with it. In some cases, people have said that it’s worked “like a miracle,” while others have said it seemed to do very little. Obviously, zeolite’s effectiveness depends on the particular kind of zeolite, the presence or absence of impurities and other natural mineral compounds, how saturated the zeolite is, the type of contaminants in the air, the quantity of contaminants, how big the room is, where the zeolite is placed, your personal expectations, and your particular olfactory sensitivity.

By the way, powdered zeolite can be sprinkled on rugs and carpets to adsorb odors. Simply sprinkle it over the surface of your carpet, give it some time to work, then vacuum thoroughly. Wearing a dust mask when doing this is suggested.

It should also be mentioned that synthetic zeolite products are also available. These use man-made minerals which are said to be of more consistent quality. One manufacturer says that it’s able to “attract and attach molecules ranging from 2-12 angstroms in size.” (10,000 angstroms = 1 micron). Interestingly, a large portion of odors and gases fit this size.


There are few measures as effective as airing, to quickly improve the indoor air quality of your home. Of course, airing simply means opening two or more windows and allowing the fresh air to pass into the living space. Ideally, the open windows should be on different walls, so that cross ventilation (the air travels across the room) can occur. Using a window fan, which you can usually buy at discount stores and building centers, can make airing even more efficient. Keep in mind that days when pollen counts and pollution levels are low are, obviously, superior times to do airing.

Incidentally, you may find that using window filters can offer some help to reduce the amount of incoming contaminants. Some are versions of electrostatic filters. While not efficient enough to stop every airborne pollutant, they’re at least able to reduce the quantity of pollen allergens from entering your opened windows.

You might be interested in knowing that add-on filters are available for window fans, too. These may be found in season at building-supply centers or hardware stores.

In general, window filters can’t be extremely efficient. That’s because very efficient filters tend to block more of the air flow, so they need more-powerful fans to move air through them. So, what if you install a powerful fan blowing out of one window, and install a very efficient filter in another window to remove the entering pollen? The problem with this is that most houses are leaky enough so that the incoming air will enter through the path of least resistance. In other words, the air will easily enter (unfiltered) through the tiny, invisible gaps and cracks all houses have, rather through the window that is now semi-blocked by the more efficient filter.

Using House Plants as Air Filters
It’s become a popular belief (almost legendary) that house plants, especially spider plants (Chlorophytum elatum variety viitum), have the capacity to clean a home’s air of most of its airborne pollutants. Therefore, spider plants, also known as ribbon plants, have almost become floral celebrities. (These plants have long slender leaves, white flower clusters, and long shoots with tiny new plants attached to the ends of them.) Unfortunately, although they’re attractive, the air cleaning capacity of spider plants has been greatly exaggerated.

Early research suggested that these plants (and also golden pothos plants, Scindapsusu aureus) were capable of fairly efficient removal of certain gaseous pollutants (but not particulates). But these initial studies, which were performed by the National Aeronautics and Space Administration (NASA) in the mid-1980s, were conducted under very limited artificial laboratory conditions. The results from this preliminary work were widely reported in the press at the time of the initial research, and they continue to be reported.

Not long after NASA’s work with plants, more comprehensive research at Ball State University simulating a real-life situation contradicted the NASA assumptions. In fact, the new studies showed that house plants were far less effective as air cleaners than originally believed—even under laboratory conditions. Therefore, although plants bring a sense of nature indoors and produce oxygen, they won’t reduce your indoor-air-pollution levels by very much at all. In fact, sometimes they can actually increase the likelihood of moisture and mold problems.

Register Filters

Recently, filters designed to be placed over a room’s furnace/central-air-conditioning registers have been marketed. Often, they’re made of a nonwoven, synthetic material and sometimes have activated charcoal or electrets (plastic with a permanent static charge to attract and hold onto certain pollutant particles) imbedded in them. Generally, they’re held in place by simple clips, sticky strips, Velcro, etc. However, while register filters sound like a good, simple, and straight-forward filtering method, they aren’t.

You see, any fabric that covers a register (even partially) will most likely restrict the air flow—at least somewhat. That may not seem like a big deal. However, even hindering the air’s passage to a small degree will set up air-pressure anomalies throughout the entire system. Of course, the more registers that are covered, and the dirtier the filters, the more the air flow is restricted and therefore, altered.
Here’s what can happen. When the airflow is restricted, the air pressure builds up inside the ducts. When the air pressure builds up, it forces air to leak out through small gaps and seams in the ductwork. (Most duct systems are actually incredibly leaky.) Because the ductwork is often located inside wall cavities, in attics, in basements, etc., it is in contact with any insulation, insect nests, mold, dirt, and debris that happens to be there. So, the air leaking out of the ducts picks up some of these pollutants and eventually leaks back into your living space. As a result, it’s possible for your home’s air to end up being more contaminated after using register filters, than before you installed them. This is all the result of upsetting the air pressures in the house.

Of course, the air pressures in your house could be upset in the first place, only to be made worse by installing register filters. Admittedly, air pressures in houses can be a complicated subject. For a thorough explanation, including all the implications, as well as solutions, you’ll want to read Understanding Ventilation, by John Bower.

Air Improvement Equipment
Often, something more than a simple odor reducing method is needed in a home. This section will cover a variety of these, ranging from the various strategies used, to descriptions of some specific equipment you might choose to purchase.
Common Strategies
Under the headings that follow are the most common strategies used in today’s air-improvement units. Because so many units use two, four, six, or even more of these approaches, it’s a good idea to understand what they’re actually capable of doing, and whether they’re really necessary in your situation—before paying extra to have multiple strategies in a single device.
Air Filters
Air filters work by letting air pass through a material (often called media). The media is designed to trap certain substances considered pollutants. Many people assume that, if they purchase an air filter, it’ll solve any indoor air problem they have. This is faulty reasoning. Air filters often aren’t sufficient to completely decontaminate a home if it has stagnant air, mildew, outgassing carpets and furnishings, or intolerable wall paint. Adequate fresh-air ventilation, proper home repair and maintenance, and the use of less-toxic construction, cleaning, and furnishing materials are always the best techniques to ensure good indoor air quality. What air filters can do is 'polish' the air. In other words, they work best if they only have to handle minor air pollution problems or polluting situations of short duration.

For those with allergies, certain particulate (small particle) air filters can help capture airborne dust-mite body parts, feces, etc. Again, however, they can’t trap all the dust-mite debris in the air. So, the best approach is to decorate and clean your home so that dust mites find it difficult to proliferate. Then, a portable particulate-removing filter in the bedroom, for example, may be all that’s needed to reduce the remaining airborne dust-mite concentration to make comfortable sleeping possible.

Incidentally, it’s important not to assume that your furnace filter will do much to clean the air in your living space. The common replaceable, thin, fiberglass type of furnace filter does little to improve your home’s indoor air quality. Actually, they are considered furnace filters, not people filters, and they are designed to only capture very large particles capable of damaging your furnace fan’s motor and other parts—not to protect you and your family’s health. However, there are some better-than-average alternative furnace filters that are specially designed to protect you and your family from airborne contaminants (at least to a certain degree).


It should be pointed out that many chemically sensitive people are bothered by air filters themselves. Even though the purpose of an air filter is to remove contaminants from the air, many also add tiny amounts of potentially problematic substances to the air at the same time. For example, many filters are held together with a resin or glue that has slight outgassing characteristics (able to emit synthetic compounds); some filters give off ozone (a highly reactive, unstable form of oxygen); and some individuals find they can’t tolerate certain types of activated charcoal (although coconut shell is often used, other types can be substituted). While an air filter may turn out to be just what you need, be forewarned of the possible limitations you may encounter.

There are several basic air-filtering methods with which you should become familiar. Knowing them will help you make a more informed choice when you’re ready to purchase air improvement equipment for your home. An important point to remember is that there are two fundamental types of filters; those that remove gaseous contaminants, and those that can trap particulates (tiny solid particles). As it turns out, only materials such as activated charcoal, activated alumina, and zeolite can remove gases—all the other types of media remove only particulates. So, if you want to capture both gaseous and particulate contaminants, the filtering equipment you select must utilize at least two filtering strategies.

Adsorption Filters
One of the most common air filtering methods currently being marketed is activated-charcoal (also known as activated-carbon). Units with activated charcoal are designed to remove polluting gases such as volatile organic compounds (VOCs), but they aren’t capable of removing all of them. Certain low-molecular weight VOCs, such as formaldehyde, aren’t adsorbed by standard activated-charcoal media (Molecular weight is the total atomic weight of all atoms making up a molecule; large, complicated molecules are composed of many atoms and, thus, tend to have high molecular weights. Formaldehyde, is a fairly simple molecule, so it has a low molecular weight.).

Surprisingly, research has shown that activated charcoal can adsorb large quantities of certain polluting gases, but can then release them slowly back into clean air. While this certainly isn’t ideal, a low average level of contaminants is better than experiencing a few large-exposure events. So, despite this characteristic, activated charcoal should still be considered an advantageous filtering material—even for chemically sensitive individuals.

On the plus side, activated charcoal is relatively affordable. However, the prices will vary depending on the particular type purchased, the quantity, and the buying source. And, of course, the activated charcoal used in filters should be replaced every few months—or whenever it no longer seems to be working effectively. Some devices using it must have an entire activated-charcoal cartridge unit replaced, others can simply be emptied and refilled.


But exactly what is activated charcoal? Defined, it’s charcoal (coconut shell is one of the more popular types, but it can also be made from coal, wood, etc.) that’s been subjected to a special steam process that causes its surface to become extremely pitted and porous. This creates a tremendously large surface area, resulting in greater adsorption capacity. Adsorption is a chemical-physical process whereby gases adhere to a surface. With a great deal of surface area, activated charcoal has a great deal of adsorption capacity. It should also be noted that some particulate matter can become inadvertently trapped in activated-charcoal media. So, it does have a limited ability in this regard, but it is primarily a gas filter, not a particulate filter.


If formaldehyde needs to be removed from your indoor air, your filtering equipment can be equipped with a specially treated activated charcoal that’s specifically designed to adsorb formaldehyde, or another type adsorption material that’s better at adsorbing low-molecular-weight gases. One substance that’s often combined with activated charcoal for this purpose is activated alumina impregnated with potassium permanganate.

To produce simple activated alumina, regular granular alumina (aluminum oxide, the compound from which commercial aluminum is derived) is heated. This causes the alumina granules to acquire a very porous, pitted structure. At this point, the granules are capable of adsorbing certain gases. Then, the activated alumina is impregnated with potassium permanganate (a dark-purplish, crystalline, water-soluble solid material). The now-impregnated activated alumina is able to adsorb an even wider range of gaseous contaminants—including formaldehyde. Activated charcoal, activated alumina, and mixtures of the two are available as replaceable filtering media, or in a complete filtering unit for use in forced-air furnace or air-conditioning systems, as well as in a “loose-fill” form for many types of portable filtering devices. Of course, like activated charcoal, activated alumina must be replaced periodically as it becomes contaminated.

If you’re a chemically sensitive person, it would be wise to experiment will several types of adsorption media to find a product that you personally find tolerable. As it turns out, some people find that they react negatively to certain kinds of activated charcoal.

It should be mentioned that activated charcoal and activated charcoal mixtures, can initially be very dusty. Therefore, if you have a new filter containing this material, it is a good idea to vacuum both sides of it thoroughly before installing it. If you are refilling a portable canister-type filter, vacuum the canister thoroughly after you fill it, and before you initially operate the unit.

By the way, it should be mentioned that non-woven polyester (or another synthetic material) impregnated with one of these media is now being used by many air-improvement-equipment manufacturers. This combination captures large particulates as well some gases. But unless there’s sufficient adsorption or absorption granules bonded to the material, it’s usefulness is limited.

Extended-Surface Filters
Extended-surface filters are made of a pleated material, usually polyester or fiberglass, that is held together with a synthetic resin. These filters are often 4–5" thick. The deep-pleated design creates a very large filtering surface, without greatly increasing the resistance to the air flowing through it—a problem that can occur with many types of filters. While some extended-surface filters are used in portable units, they’re also made for whole-house applications. In such cases, they usually require the installation of a special housing in which to mount them. Such a housing would be permanently installed in the duct system of a forced-air furnace or air conditioner. It should also be mentioned that 1"-thick extended-surface filters are also available. These can be used as a simple replacement for your standard (inefficient) furnace/air-conditioner filter.

Extended-surface filters are fairly effective as particulate filters. In fact, they’re actually classified as medium-efficiency filters. They’re designed to trap many types of the airborne solids, including most pollens. However, they aren’t capable of adsorbing gases. Extended-surface filters are usually moderately priced but, in whole-house systems, they will require the services of a professional heating and cooling contractor to initially install the housing in your duct system. As with most filters, the media (the pleated material) must be replaced periodically. Once the housing is in place, you can change the media yourself, something that is typically done once a year.

One consideration to keep in mind, especially if you’re a chemically sensitive person, is that the synthetic materials making up these filters can give off slight odors. However, some people have found that by putting a new filter in their oven at a low temperature (200°F or less), for about two hours, it often helps eliminate most bothersome smells. If you’re considering this, first contact the manufacturer to see if its filter will withstand such a procedure.

If you decide to go ahead and “bake” your extended-surface filter, make absolutely certain that you have adequate ventilation when you do it. You should close off your kitchen from the rest of the house, open the kitchen windows, and operate the range-hood fan (vented to the outdoors) on high speed. Once the filter has finished baking, use hot pads or oven mitts to place it outdoors to cool. However, continue to keep your kitchen windows open and the range-hood fan turned on for at least 30 minutes, and heat the oven up to a high temperature to burn off any odors that may have accumulated within the oven itself.
HEPA and ULPA Filters
A HEPA filter is a very special type of extended-surface filter. The acronym HEPA stands for high efficiency particulate arresting (or sometimes air or accumulator). Interestingly, these filters were originally developed by the U.S. Atomic Energy Commission (AEC) during World War II to trap radioactive plutonium particles in nuclear laboratories.

HEPA filters are generally made of fiberglass or polyester fibers held together by a synthetic resin. These filters have extremely tiny pores, so the airflow through them is very restricted. Therefore, powerful fans (which are often fairly noisy) are necessary to forcibly push air through them. HEPAs are sometimes termed absolute filters, and it’s easy to understand why. HEPA filters are capable of trapping 99.97%, or more, of particles as small as 0.3 microns (a micron is one millionth of a meter)—some are designed to be even more efficient. Not surprisingly, vacuums fitted with very efficient HEPA filters are used during asbestos-cleanup operations. HEPA air filters are commonly used in research laboratories, and in the manufacture of delicate electronic components. However, although these filters are very effective at removing particulates, including dust-mite body parts and feces (which are relatively large), they’re unable to remove any contaminating gases.

HEPA filters have other drawbacks as well. For example, they’re usually fairly expensive. Therefore, to extend the life of the HEPA filter itself, most filtering units that use HEPA technology have one or more prefilters to first capture most of the larger particles. With a prefilter, the HEPA media will usually only need to be replaced annually.

It’s important to note that some sensitive individuals find that the synthetic material used to make HEPA filters gives off odors they find to be bothersome. In a few cases, despite the advantages of particulate-free air, these odors have proven to be intolerable. However, if an activated-charcoal filter is used after the HEPA filter, this will usually minimize any objectionable odors. Yet, you should also understand that most people, even many allergic or chemically sensitive ones, often don’t require the tremendous efficiency of a HEPA filter anyway. Unless someone smokes in your home, other less-efficient filtering approaches will often work just fine to remove many of the common allergenic pollutants.
It should be added that recently, ultra-efficient ULPA (ultra low penetration air) filters are now available. These have an efficiency of 99.999% at capturing very minute particulates as small as 0.12 microns. These require even more powerful fans to force air through them. An ULPA in-home air filter is often a case of “overkill” because it’s doubtful that the added capturing ability will make any difference in the health of most users. Actually, even though they are microscopic in size, mold spores and pollen grains tend to be relatively large particulates, so even a HEPA can be overkill—if that’s all you’re interested in capturing.
Electrostatic and Electret Filters
Electrostatic and electret filters, rely on electrostatic force to work. An electrostatic force causes similarly-charged molecules to repel and those with opposite charges to attract. These types of filters rely on simple static electricity, rather than live electric current, for their electrostatic charge.

Electrostatic filters are made of a special plastic media, such as vinyl, polyester, or polystyrene, and they are typically about 1" thick. Most filters of this type are meant to replace typical standard forced-air furnace/air-conditioning filters. Some companies also offer models that fit in windows.

Some electrostatic filters become statically charged as a result of the friction of the air passing through their synthetic media. However, other types are precharged, using electrets. An electret is a special plastic material that has a permanent static charge. Electrets get their charge after being melted and resolidified in the presence of a very strong electric field.

In the filtering process, those particulates in the air that happen to be charged are attracted to—and adhere to—the portions of the plastic electrostatic filter media that carries an opposite charge. Models using electrets, in particular, often have both positively and negatively charged areas in their makeup. It should be noted that, of all the particulate pollutants in the air, many are positively charged—although others are negatively charged or uncharged.

Electrostatic filters are relatively inexpensive and constructed so that the air flowing through them is only slightly restricted. While these filters aren’t extremely efficient, they are able to capture many mold spores and pollen grains. Of course, electrostatic filters are not capable of trapping gases of any kind.

Sometimes, dirty electrostatic filters can be washed off so their surfaces are again able to capture particulates. However, this should be done only if the manufacturer allows it. Most electrostatic filters should be replaced when they’re no longer capable of retaining an electrical charge. This will vary with the brand, and how dirty the air in question is. It should be noted that the plastic media can sometimes be bothersome for certain sensitive individuals.
Polyester and Other Synthetic Material Filters
Polyester (or another synthetic fiber), often in a nonwoven form, is used in many air-improving devices. Sometimes it’s a relatively thin fabric, in other applications it’s much thicker and loftier. In either case, it’s inexpensive to produce, and it can usually filter out fairly large particles. Therefore, it’s the most common media used as a prefilter for a HEPA filter, as well as in units that rely on multiple air-filtering strategies. By the way, many synthetic-fiber filters can often be hand washed, allowed to air dry, and then reinserted—so they may rarely need replacing.


Today, it’s not uncommon for polyester (or another synthetic fiber) to have other compounds and substances added to it. This might be some type of biocide, which would be added to inhibit the bacteria and mold that could otherwise grow on it, and subsequently contaminate the air. One of the more inert antimicrobial treatments is Aegis Microbe Shield (Aegis Environments) which was developed by Dow Corning Corporation. This patented technology uses organosilicon agents which are extremely minute crystals of silicon (one of the main components of sand and glass). These are permanently “covalently or ionically bonded” to the surface of the filter media. This means that bonding is on a molecular level, and it does not involve glues or other types of adhesives. So, items containing Aegis Microbe Shield can be repeatedly washed, and it will not come off. Another plus is that it’s also considered “non-sensitizing.” How Aegis specifically works is by “mechanical interruption of cell walls.” In other words, the microscopic silicon slivers literally stab mold and bacteria to death. Therefore, no poison of any kind is necessary. One brand of filters that use this technology is Purolator.

Other polyester (or other synthetic fiber) filters have an innate static charge to attract and hold onto particles. Still others have electrets imbedded in them.

Probably the most popular addition to these types of filters is an adsorbent media such as zeolite, activated charcoal, and/or activated alumina with potassium permanganate. With an adsorbent material, the polyester material can now function to remove both particulate and gaseous air pollutants. Of course how successfully this is accomplished depends on the amount of adsorbent actually present. If there’s only a small quantity, then only a minimal job will likely be done. If there’s a great deal, then you can expect more gases to be removed. By the way, if a glue or resin is required to hold the adsorbent granules in place, it could add its own odor, which could pose problems for some very sensitive persons.

Electrostatic Precipitators

Electrostatic precipitators, also known as electronic air cleaners, don’t operate by “straining” pollutants out of the air, like the filters discussed above. Therefore, technically they aren’t called filters, however, they do capture and retain pollutants. Today, most electrostatic precipitators are designed to be permanently installed in the ductwork of forced-air furnace/air-conditioner systems, although some portable filtering units also use this technology. (Note: These units will not trap contaminating gases, they only work on particulates.)

Electrostatic precipitators, like electrostatic filters and electrets, rely on electrostatic force to remove pollutants from the air (Electrostatic force causes like-charged molecules to repel, and those with unlike charges to attract.). However, while the electrostatic filters and electrets discussed above use static electricity, electrostatic precipitators require live current to do their job. There are other major differences as well.

Electrostatic precipitators contain metal wires that have a strong electrical charge. As the air passes by these wires, any particulate matter in the air takes on the same charge as the wires. The air (with its now-charged particulates) then passes into a collection chamber containing a series of metal plates. These plates have also been charged, but with a charge that’s opposite of the wires. As a result, the charged particulates become attracted to the collection plates and cling to them.

As it turns out, dust and debris clinging to these plates can quickly build up. This causes electrostatic precipitators to steadily, sometimes rapidly, become less and less efficient. Therefore, the metal plates in electrostatic precipitators must be removed and cleaned periodically, in extreme cases this can be as often as once a week. Fortunately, these plates can be washed satisfactorily by simply placing them in an automatic dishwasher. Hand washing in a tub is also possible. All you do is slide the unit out of its housing (this automatically disconnects the electricity), then you clean it, and replace it.

One notable feature of electrostatic precipitators is that, unlike other filters, they have virtually no restriction to the flow of air. This is because there’s no actual media of any type to hinder the air’s passage through the unit. Therefore, there’s also no filter media to replace, which is another advantage. However, electrostatic precipitators are relatively expensive, they are certainly not as efficient as HEPA filters, and they can quickly lose much of their effectiveness as they get dirty—unless they’re regularly cleaned.

Electrostatic precipitators also produce a small amount of toxic, reactive ozone (O3) gas when they are operating. However, a filter containing activated charcoal, which is installed after the electrostatic precipitator, can usually adsorb any ozone that has been produced. You should also know that tiny electric sparks can be generated inside electrostatic precipitators. These can be heard as a slight “popping” sound that some people find irritating. In addition, the sparks can cause some of the particulate matter, that is attached to the collection plates, to be released back in the air you breathe.

Ultraviolet (UV) Air Purifiers

Ultraviolet (UV) air purifiers have the capacity to kill (or inactivate) some types of molds, bacteria, and viruses. This ability, however, varies with the specific microorganisms exposed (and it also depends on the life stage they’re in), the wavelength and intensity of the UV light, as well as the duration of the exposure.

What is UV light? Ultraviolet light is a particular form of electromagnetic radiation. It can have a wavelength from 15 nanometers (nm) long up to 400 nm, which is the beginning of the visible-light range. So, UV radiation is shorter than the waves of visible light, but longer than X-rays. Interestingly, because it’s not in the visible-light range, our eyes can’t see it. (It was only discovered in a photochemical experiment in 1801.)

Of course, everyone knows that UV light from the sun can cause sunburn. But it can also cause skin cancers and cataracts. When microorganisms are exposed to it, the UV is absorbed by their cell nuclei. This causes chemical alterations in the genetic material stored there, and it’s these changes that ultimately prove lethal. Interestingly, it’s been shown that the most effective UV light for sterilization (extermination of microorganisms) is in the 220-300 nm range. (This is called the abiotic range, which means that it is non-life sustaining.) As a result, it’s in this range that UV germicidal lamps emit radiation.

While UV light has been shown to be useful against certain airborne infectious germs (this was first demonstrated in 1947 with studies involving tuberculosis bacilli), it’s not been widely used, even in hospital settings. This has primarily been because the UV light can cause eye irritation, or damage, from not only the lamp, but also from reflections off other surfaces in the area. Another problem has been that UV lamps (which are typically low-pressure mercury-vapor tubes) must be kept immaculately clean to perform optimally. Also, these lamps typically degrade quickly during the first 100 hours they’re on. In fact, commercial tubes are usually rated as though they’ve already past the 100-hour mark.

However, there are even more drawbacks. For example, while typical UV exposure may kill certain microorganisms, others are temporarily “put out of commission” into a state that’s termed inactivation. While this inactivation is due to the damage caused by the action of the UV light, a certain percentage of microorganisms can sometimes reactivate (repair themselves) in the presence of visible light or, in other cases, in darkness. Plus, studies have apparently shown that UV is not particularly effective against a number of microorganisms, such as airborne HIV. (HIV requires twice the amount of UV to be killed compared to other viruses.)

However, a bigger impediment to the widespread use of UV sterilization is that it can only affect those microorganisms that are actually exposed to it. If other germs are in a room’s air that haven’t been in the UV’s presence, they will be unaffected, so they’ll simply go on multiplying. Then, too, as soon as someone (or a pet) walks into a UV-treated room, a whole new set of microorganisms will reinfect the sterilized area. So, UV light is often best used for a small, focused job, rather than for general room air purification.

While UV air purifiers can be purchased as stand-alone units, they’re now being incorporated in multi-strategy air filtering devices. As has been mentioned, you should keep in mind that they’re only going to be partly effective at de-germing your home. However, if the purpose of the UV radiation is to purify the air coming into the filter, so that the filter itself will be less likely to become contaminated, that may be more do-able. Another thing to keep in mind with a UV purifier is that the ultraviolet light will create a small amount of ozone (O3) as it reacts with microorganisms. Plus, the UV lamp will need to be replaced in time. (It is often best to replace it before it burns out because of lamp degradation.)

For more information on ultraviolet purification, you may want to check out a technical book on the subject, Disinfection, Sterilization, and Preservation edited by Seymour S. Block, Ph.D. which should be obtainable through a technical library.

Ozone Generators
Ozone generators produce ozone (O3) by continually creating electrical discharges. Often, the generators are designed so that this rate of production can be increased or decreased. But why do some people feel the need to use ozone generators as air cleaning devices? After all, ozone is a pungent-smelling, irritating gas. Because it’s a very unstable form of oxygen, it’s extremely reactive. In sufficient concentrations, it can severely irritate your skin, eyes, and mucous membranes. Ozone can also cause you to have breathing problems.

Ozone generators are usually thought a good idea because ozone is a powerful oxidizing antiseptic that’s capable of killing many forms of bacteria and mold. (Unfortunately mold, either alive or dead, can provoke allergies.) Ozone can also reduce smoky odors in a home after a fire. However, to remove smokiness effectively, the ozone must be at a fairly high concentration. In either case, if you need to kill mold or remove smoke odors, it’s best to leave this work to professional contractors. When a professional is operating such equipment at high concentrations, no one should be inside the house, and it should be aired out thoroughly afterwards.

Interestingly, a number of chemically sensitive persons have bought ozone generators to purposely break down airborne volatile organic compounds (VOCs) to which they would normally react. As it turns out, while ozone can break down some VOCs in the air, it can also react with some existing gases, or other materials and furnishing in the home, and create bothersome new pollutants—ones that weren’t there before. Obviously, ozone is not the answer.

The truth is, ozone is a dangerous substance and should not be purposely added to a home’s indoor air by homeowners. You should be aware that lawsuits by various governmental agencies have been filed against one of the largest makers and marketers of ozone machines—for unproved claims. The EPA (Environmental Protection Agency) is so concerned about the potential problems of ozone use in homes, that they’ve devoted space on their Web site to discussing its dangers. To sum up, ozone is not recommended for consumers to use in their homes, period.
Negative-Ion Generators
In recent years, negative-ion generators have become popular as air-cleaning devices, and even more recently, they’re becoming included in multi-strategy air improving equipment. But exactly what are they? Negative-ion generators are actually specialized electronic devices that are capable of using electric current to create negatively charged ions—in this case, free electrons. These electrons are immediately spewed out into the air where they quickly attach themselves to airborne particulates, in the process giving them a negative charge. The newly negatively charged particulates then usually leave the air and cling to surfaces such as walls and ceilings that tend to be positively charged. This adhesion occurs because of the action of natural electrostatic force in which like-charged molecules repel but unlike-charged molecules attract.

Although most users of negative-ion generators won’t notice it at first, their walls and ceilings will usually become steadily dirtier as the pollutant particles accumulate on them—although the air itself will likely be less contaminated. Therefore, it’s necessary that these collecting surfaces be cleaned from time to time. However, you should realize that this is not only for aesthetic reasons. As it turns out, many pollutant particles will eventually reenter the air as they lose their negative charge. To counter this problem, some negative-ion generators have built-in air filters or collection plates so that the particles are more likely to be trapped inside the units themselves.

Unfortunately, it’s doubtful that negative-ion generators can substantially clean air that is very polluted. And, they are apparently not particularly effective in reducing dust-mite allergens. Plus, charged particulates will apparently deposit in the respiratory track more readily than non-charged particulates. However, a Columbia University study released in 1995 found that negative-ion generators did help to alleviate some of the symptoms of SAD (Seasonal Affective Disorder), a depressive condition that occurs during the cold months of the year to some people. This may be due to the fact that an excess of negative ions in the air can, apparently, give a person a sense of well being. While this effect isn’t well understood, the opposite effect has also been reported.

So, for those with the “wintertime blues,” and perhaps in situations where allergic or sensitive individuals are unable to tolerate other air-cleaning devices, or they can’t afford a more efficient device, stand-alone negative-ion generators may be beneficial.
Mechanical Ventilation Systems
A mechanical ventilation system is an excellent way to efficiently and effectively improve your home’s indoor air quality. By using exhaust fans or more elaborate equipment, fresh air will be able to come into your house and stale air will be expelled outdoors. However, the technical nature of this important topic is well beyond the scope of this article. So, for complete information on all types of residential ventilation systems including heat-recovery ventilators, also known as HRVs (these units are able to transfer a portion of the heat from the outgoing air into the incoming air, or vice versa), read Understanding Ventilation by John Bower.

Choosing the Right Air-Improvement Equipment

Before purchasing any air-improvement device, it’s best to rectify your home’s air problems by other means first, as much as possible. This is because air-improvement equipment works best when it only has to cope with minor air pollution problems. Therefore, its wise to eliminate as many known sources of contamination (mold, perfume, tobacco products, noxious cleaners, dust mites, etc.) as you can. After doing that, you should determine what contaminants remain in the air. Then you can consider a unit designed to eliminate those sorts of pollutants.

Unfortunately, as has already been mentioned, filtering methods that are capable of removing particulates, such as pollen grains or house dust, can’t remove gaseous pollutants, such as volatile organic compounds (VOCs), and vice versa. However, many models are now available that combine adsorption and one or more particulate trapping methods. Sometimes, even more strategies are included such as UV light purification or negative-ion generation. This is especially true with portable room-sized units.


Besides offering differing strategies, the various air-improvement devices come in a variety of sizes. These range from tiny desktop units to permanently mounted, built-in, whole-house models. Obviously, in many situations, the very small units are just too small to accomplish very much. On the other hand, whole-house models may not be practical, particularly if you’re renting. Therefore, it’s important to pinpoint the types of contaminants that need to be removed, as well as the areas where they’re found in your home. If these areas include most of your house, then a whole-house model could make good sense. However, if only your kitchen, or a single bedroom, needs improvement, then room-sized units might make more sense.

In addition, you should consider what special qualities you desire in your unit. For example, how should it be constructed? If you’re chemically sensitive, you may prefer a model housed in a metal casing, as well as one where the fan motor is placed upwind of the adsorption filtering media, in order to capture any potentially bothersome odors. If the unit is to go in a bedroom, it can be important to select an especially quiet model, or one with two, or more, fan speeds. That way, it could be run through the night without keeping everyone awake.

Of course, you should also consider how much you’ll be willing to spend. And, you should honestly evaluate how willing you are to maintain the unit. Are you the type of person who would be willing to wash an electrostatic precipitator’s collection plates routinely? How often are you willing to order and replace your filter’s media? Are you the type who doesn’t mind going down into the basement occasionally, opening up your furnace, and checking to see if the electrostatic filter is dirty? Finally, you should take into consideration any guarantees or warranties.

Of course, if you’re a chemically sensitive person, or you have asthma or serious allergies, it would be a good idea to ask for air-equipment recommendations from your physician, or other health-care professionals. Also, talking with friends who currently own units should provide you with some useful information. In addition, to help you choose, independent consultants are available.

Whole-House Equipment
Whole-house air improvement equipment offers the major advantage of being able to process all the air that’s circulated within your home. Some models are actually very simple and are used in place of a typical standard furnace filter. However, others require a special housing, and professional installation—and they can be expensive.

Before investing in complex and costly filtering/cleaning units, you would probably find it advisable to speak with an engineer or architect who is familiar with airflow complexities, solving particular pollution problems, and the construction of various units. Installation of such equipment should be undertaken only by knowledgeable individuals.
Portable Room-Sized Equipment
A large number of portable air-improvement devices are now available. In fact, there are so many that it can seem overwhelming to decide on exactly which unit to pick. However, no matter which model you choose, if you’re a chemically sensitive person it’s best if it has a metal cabinet with any fan motors upwind of the adsorbing filtering media.


It should be noted that some highly allergic or very sensitive people may need to try several brands or models of filters before finding one that meets all their needs, and is tolerable. Therefore, it’s a good idea to ask a dealer if it’s possible to rent, rent-to-buy, or have a trial period to determine if a particular unit is right for you. Often, at the very least, you’ll have a period of allotted time before your purchase must be returned in order to receive your money back. Saying this, you should only buy a unit if you have done your homework ahead of time, and expect to keep it from the start. It’s not fair to a dealer or manufacturer to “try on” a myriad of devices as you would shoes at a shoe store.

Wearable Air Filters and Negative-Ion Generators
There are filters and negative-ion generators now made to be worn. Some of these are described below.

Personal Facial Air Filters

Some chemically sensitive and allergic individuals have found it helpful to wear personal facial filters when doing tasks that usually provoke negative symptoms in them, such as reading a magazine (to protect against ink and paper odors), or cleaning the house (to filter out dust). Surprisingly, there are several types available.

One-hundred-percent-cotton masks made to hold an activated charcoal insert, are available from several companies. The granular activated charcoal will adsorb many bothersome odors.

An interesting option, along the same line as the above filters, are bandit scarf face-and-neck-covering filters. Ones of unbleached, 100%-cotton with dust-free woven, replaceable, activated-charcoal filters are available. These masks are secured with a neck strap and have an adjustable strip at the nose bridge.
Disposable dust masks are another option which are designed to trap most larger particulates. As a rule, these are made of synthetic fabrics and materials. So, if you’re a very chemically sensitive person, you may find that you have trouble tolerating them.

For more protection when doing certain odorous home hobbies or remodeling products, especially if a potentially noxious product must be used, a respirator mask is a much better choice. These may be found locally in hardware and building-supply centers.

Personal Negative-Ion Generators

One of the newer items you can find are personal negative-ion generators. Usually, these are tiny plastic units that come with a cord to hang around your neck. Internally, their battery-run electronic workings spew out negatively charged ions.

These ions are supposed to attach themselves to airborne particulates near the wearer’s head and prevent them from being inhaled. There are a number of doubters when it comes to the usefulness of negative-ion generators, and in this mode, they seem even more suspect. However, for helping to alleviate SAD (Seasonal Affective Disorder), they may help. Yet a problem with any negative-ion generator is that they create reactive ozone in the process of making free electrons. Many of the companies who make personal negative-ion generators say that the quantity of ozone produced is extremely small. Yet, no amount of ozone is beneficial to breathe.

Breathing-Aid Equipment For Asthmatics
If you or your child has asthma, check with your doctor for the appropriate equipment you may require. Often, these are prescription-only items. Helpful books on peak flow meters, etc. are available.
Air Humidification
In dry climates, or during the heating season, it might seem that humidifying (adding moisture to) your indoor air would always be the logical, healthful thing to do. After all, if the relative humidity of your home air is very low, your eyes, skin, and mucous membranes could become irritated, your lips might crack—and your wood furniture could become dry enough to shrink and become unglued. However, there are other considerations to keep in mind. Therefore, in the sections below, the actual pros and cons of humidifying your home are discussed, as well as specific methods of humidification you might choose to use.
Simple Humidifying Strategies
If you feel you want to raise the relative humidity level in your home, there are some very simple things you can do to accomplish this. One of these is to merely lower the room’s air temperature. The cooler a room is, the higher its relative humidity—as long as it’s holding the same amount of water vapor. Other approaches you might try are opening your bathroom door immediately after you shower or bathe to let the moisture-laden air spill out into the rest of your house, boiling distilled water in a pot on your stove, putting distilled water in clean pans on your steam radiators, and misting the air with distilled water in a spray bottle. By the way, it is always best to use distilled water, rather than tap water because tap water can add particulates such as minerals or bacteria to the air.

In addition, by merely drinking more water during the winter months, you’ll help keep your mucous membranes more moist. Of course, if you use a tolerable body moisturizer and lip balm each time after you bathe, you’ll help retain more water in your skin. You might also want to use tolerable eye drops to help soothe your eyes as well.


The reason houses get too dry indoors in the winter is because they are over ventilated. This can happen in a house even when it doesn’t have a mechanical ventilation system. This is because air moves naturally through the tiny invisible cracks and gaps (that all houses have) more readily when it is colder out. So, during the coldest part of the year, you often have more air exchange than you really need. This means that there is too much dry outdoor entering. The solution is to weatherize your home. In that way, you will save energy, and be less dry in the winter. For more on the implications of tight vs. loose construction, how tightness affects the indoor air, and controlled mechanical ventilation, you’ll want to read Understanding Ventilation by John Bower.

If, despite the above measures, your home still feels too dry, you might try adapting to the more arid conditions—in other words, acclimating yourself. This may take several weeks. However, if you still find that the low-humidity levels are unsatisfactory, only then will you want to consider using a humidifier. This is because several problems are associated with using humidifiers.

To increase the relative-humidity level in homes, humidifiers are commonly used. Humidifiers are simply devices that are designed to increase the air’s moisture content. Today, there are several approaches to doing this, such as producing steam, or several methods of creating a cool mist. It should be pointed out that different humidifiers are capable of humidifying different sized areas. For example, a particular unit may be appropriate for either a single room, a portion of the house, or the entire house. In addition, humidifiers are equipped with different features—such as an automatic shut off, adjustable vents, etc.—and different prices.

Unfortunately, many humidifiers have innate problems associated with them. These can include spewing out bothersome odors (from plastic, rubber and vinyl parts, or oily odors from fan motors) as well as mold and other biological growth (which can quickly contaminate certain humidifiers). Of course, these are of special concern for sensitive and allergic persons, but they’re not healthy for anyone to breathe.

If you opt to go ahead and purchase a humidifier anyway, it would be a good idea to monitor the humidity level of the room(s) often, so that excess moisture isn’t accidentally added to the air.

You’ll also want to only use distilled water, which will be free of mineral particulates and biological contaminants. In addition, you’ll want to thoroughly and frequently clean your humidifying unit. Finally, it’s best to avoid using scented additives (or chemical disinfectant additives) that some manufactures include with their new units, especially if you’re a chemically sensitive or scent-allergic person. The odors from these will not only get into the air and eventually into everything in the room, but they’ll become absorbed by the humidifier’s plastic, rubber, or vinyl parts.
Humidifier Types
Several different humidifying strategies are in use. The following sections discuss these. (For suggestions on what specific humidifier is best for you, see Choosing the Right Humidifier below.)
Steam Humidifiers
For many years, electrically operated steam (or vaporizer) humidifiers have been popular to increase indoor humidity. These units, sometimes also called warm-mist humidifiers, contain electric heating elements that boil water to produce steam. Typically, these are room-size models with plastic water reservoirs. However, some steam humidifier devices are designed for whole-house installations in forced-air furnace ducts. Some of these are constructed primarily of metal.

Steam’s major advantage, as a source for humidity in your home, is that its high heat destroys virtually all the microorganisms that might be present in the water. However, if you get too close to certain portable units, you could burn your nasal passages, skin, or eyes. However, it must be said this not likely to happen because the steam cools quickly just a very short distance from where it’s emitted.

Some people fear that electric steam units might be dangerous because they could tip over and spill out boiling water. However, many models are now designed to seal completely, so that spilling is unlikely. Yet, there’s always the inherent, potential danger, posed by any electrical element, of overheating and causing a fire. Fortunately, the units generally available today have safety features to help prevent such accidents from occurring, such as an automatic shutoff when the water level in the reservoir is too low or when the unit is tipped over.

Remember not to use hard water (water with high mineral content) in a steam humidifier or vaporizer. Otherwise the dissolved minerals will create a mineral scale buildup on the heating element and around the vent opening. If this happens, it will lead to higher energy use as well as inefficient dispersal of the steam. Plus, if hard water is used, extremely fine particulate minerals, which aren’t good to breathe, will be spewed out into the air, along with the steam. Some manufacturers now recommend that you only use distilled water in their units for these very reasons.

As with any humidifier, steam units should be cleaned regularly. If minerals should build up on the elements, read your owner’s manual for suggestions on proper and effective cleaning. In addition, when your portable steam unit isn’t actually in use, unplug it and empty the reservoir.
Cool-Mist Humidifiers
Cool-mist humidifiers spew out unheated water in a very fine mist. They’re available in small portable units as well as models designed to humidify your whole house. As a rule, they tend to be constructed with plastic water reservoirs and other parts. Often, vinyl or rubber parts are included, too. Cool-mist humidifiers eliminate all the potential problems associated with boiling water, such as the hot vapor and hot elements. However, they don’t offer the sanitizing effect of high heat, so microbial growth often contaminates these units. As a matter of fact, as they dispense misted water, they also spray out microbes, dissolved minerals, and anything else that happens to be in that water. Once these contaminants are airborne, you and your family will wind up breathing them.


Therefore, if you opt for this type of humidifier, use only distilled water in it. It’s also extremely important to clean the unit frequently to prevent any mold problems. If possible, choose a unit with a Ultraviolet-light purifier to help decontaminate the air entering the room from the humidifier. And, of course, remember to unplug small portable models when not in use, and empty the reservoir.

Ultrasonic-Dispersal Humidifiers
Ultrasonic-dispersal humidifiers are actually specialized types of cool-mist humidifiers. These are most often seen as portable models, usually made of plastic. Ultrasonic-dispersal humidifiers work by using high-frequency sound waves to shatter water droplets, creating an ultra-fine mist. However, they also break up any minerals and microorganisms that may be present in the water. Unfortunately, the very fine particles of such debris should not be inhaled over an extended period.

Therefore, it’s again extremely important to only use distilled water in ultrasonic-dispersal humidifiers. Also, frequent cleaning is necessary to prevent any mold problems. It’s also not a good idea to leave water in the reservoir of a portable unit, or leave it plugged in, when not in use.
Evaporative Humidifiers
Evaporative humidifiers humidify by blowing air across, or through, some type of water-saturated media, and then out into the room. The specific methods to accomplish this differ among the various models. For example, some use a rotating drum, others a conveyor apparatus, and still others use a large wick. The absorbent media often consist of a synthetic foam or other spongy material. Evaporative units come in both room-size and whole-house furnace installations. The portable units generally have plastic water reservoirs and plastic housings.

Over the years, evaporative humidifiers have become notorious for producing some of the worst problems associated with humidifiers. These include mineral build up, as well as microbial growth (mold, bacteria, etc.) contaminating the water reservoir and the media. Of course, all this “stuff” will become airborne, and will be inhaled by you and your family when these units are operating. It should be mentioned that some units come with an air filter, through which the air passes, just before entering the room air. However, these filters are usually not very efficient, and they can become easily contaminated with mold, etc.

Therefore, if you’re interested in a portable evaporative humidifier, it’s very important that you only use distilled water in it. It’s also vital that you keep the unit as clean as possible and never leave standing water in the reservoir when the humidifier is not actually being used. Also, remember to unplug the unit when it’s not in use as a safety precaution.
Choosing the Right Humidifier
Before purchasing any humidifier, you should determine the size of the area you plan to humidify (one room or the whole house), have a price range in mind, and evaluate your own inclinations: Are you willing to monitor your room’s humidity level, to regularly clean the unit, perhaps daily, and buy and install any replacement filters, etc.? You also should decide on a basic humidifying strategy. Next, give some thought to the unit’s construction (what materials is it made of, and how easy will it be to fill and clean), its special features (an auto shutoff when the reservoir is empty, or an ultraviolet light purifier, etc.), and any guarantees or warranties.

Unfortunately, it should be pointed out that there are really few truly healthy humidifiers from which to chose—and this is particularly true from the perspective of chemically sensitive individuals. After all, most humidifiers are constructed with plastic reservoirs and housings, often with internal parts made of various synthetic and rubber compounds. Generally, these materials have the capacity to impart their own odors into the humidified air, especially when the humidifiers are new. Also, frequent cleanings are required to prevent any mold problems.

Then, too, whole-house humidifiers, that work in conjunction with furnaces, may encourage mold and mildew growth inside your ductwork simply by raising the relative humidity levels there. In addition, if your humidifier doesn’t have an adjustable humidistat (a device able to detect relative-humidity levels and turn off the humidifier when a preset level has been reached), and you don’t regularly monitor your room’s moisture level yourself, your humidifier can easily introduce too much moisture into your home. This situation can lead to a number of problems, including damage to your walls, and increased populations of microorganisms.

However, if you decide you really need a humidifier, a simple portable steam/vaporizing (warm mist) unit is often one of the better choices. Although it’ll likely have the usual plastic reservoir, some of the simpler models have a minimum of other synthetic or rubber components. Also, in their favor, the high heat they generate is disinfecting. When it’s new, it’s often a good idea to run your steam humidifier (or any other type of new portable humidifier) for sometime outdoors in dry, uncontaminated surroundings until the plastic odors are no longer noticeable in the vapor that is released. (Of course, this is very important if you’re a sensitive person.)

Portable electric steam/vaporizer (warm mist) humidifiers are still relatively popular. Therefore, models for baby and children’s rooms are often sold in local drugstores. More elaborate models, are sold in many department stores, discount stores, and building centers.

If you decide you’d like a whole-house humidifier that would be permanently installed in the ductwork of your forced-air furnace, a steam type would probably be best. Several brands of these are currently available, so check your local heating/cooling contractor to see what they’re currently handling.

(Note: The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)



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Improving Your Indoor Air:  Created on May 28th, 2007.  Last Modified on February 27th, 2011


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