Air Purifier Buying Guide

Air Purifier Buying Guide
Polluted air trapped inside a tightly sealed house Quality air purifiers have never been more important for good health. The tight seals that make your home comfortable and energy efficient also make the indoor air more polluted. The air inside your home is five to ten times dirtier than the air outside, and Americans spend 90% of their lives indoors.

Shopping for the right air purifier can be confusing and frustrating. Some air purifiers on the market today actually pollute the air with harmful levels of ozone, a powerful lung irritant that can be especially dangerous to asthma sufferers. Others can simply confuse you with the sheer number of options, sizes and prices available. While comparing all these options can be overwhelming. No matter the brand, price or style of air purifier you are searching for, there are key things to look for with any unit. To help you learn about air purifiers and find a safe, effective unit that is right for your needs, we created this air purifier buying guide.

Common Household Air Pollutants

Different air purifiers target different pollutants, so it is important to identify which pollutants you want to eliminate from your home before you buy an air purifier.

  • Airborne Particles include pet dander, dust mite allergen, pollen, plant spores, fungi, mold, and tobacco smoke, and they are the most common cause of indoor allergy and asthma attacks. A HEPA air purifier is the best method of eliminating airborne allergens. Here is a look at the average particle size of some common indoor airborne particles:

Common Household Air Pollutants

  • Household Odors and Gases include cooking odors, kitty litter, tobacco smoke, various toxins, and gaseous pollutants like indoor pesticides or aerosols. Activated carbon filters are ideal for adsorbing gases and odors that are too small to be trapped by a HEPA filter. "Adsorb" is not a typo; "adsorption" occurs when materials attach through a chemical reaction.
  • Volatile Organic Compounds (VOCs) are found in a wide variety of common household products: paints, varnishes, cleaning supplies, disinfectants, glues and adhesives, and even new carpet and building supplies. Look for ingredients like benzene, chloride, formaldehyde, ethylene, and toluene. VOCs can cause the following symptoms: irritation of the eyes, nose, and throat, headaches, nausea, and even severe chronic health conditions such as damage to the nervous system. The presence of VOCs can also exacerbate asthma.
  • Micro-organisms include antigens, pathogens, bacteria, and viruses. They are the everyday germs that make us sick. Mold is also considered a micro-organism.

Air Purifier Filter Types

Different air purifier filters target different types of air pollution. HEPA air purifiers are the most popular, and they are perfect for eliminating household allergens such as dust, animal dander, and pollen, but they are not very good at capturing ultra-fine particles like viruses or eliminating foul odors, organic compounds, or chemical fumes.
HEPA Air Purifiers
Because different air purifier technologies have different strengths and weaknesses, many modern air purifiers combine two or more filter or media types in the same unit. For example, our #1-selling Austin Air Healthmate utilizes a HEPA filter along with a thick bed of activated carbon to help eliminate dust and odors. Regardless of the filter media used, always look for some mention of a "sealed system" or similar terminology. The best filter in the world is literally worthless if the unit leaks air and allows purified and dirty air to mix. With that being said, let's take a closer look at the different types of filters:
  • HEPA (High Efficiency Particulate Air) Filters set the standard for air purification. By definition, a HEPA filter removes at least 99.97% of all particles as small as 0.3 microns. HEPA air purifiers were originally developed by the Atomic Energy Commission to capture radioactive dust particles. HEPA filters allow only very small particles to pass through them. Allergens such as pollen, animal dander, mold spores, and dust get trapped in the filter. The main disadvantage of the HEPA air purifier is that you have to periodically change the filter. The main advantage: if it is HEPA certified, then you know it works well. Not all HEPA filters are created equal. Size matters: the more square feet of HEPA filter, the more particulates it will be able to remove. The size, material, and construction of the actual filter media all play a role in the air purifier's performance and may account for why one HEPA filter is more expensive than another.

Air Purifiers offering HEPA filtration: Austin Air, Blueair, IQAir, Honeywell, AllerAir, Alen, Airgle, NQ Clarifier, Amaircare, Germ Guardian, and Whirlpool.

  • Ion Generators and Ozone Generators create charged particles (ions) and emit them into the surrounding air. These ions combine with impurities (like dust) in the air, forcing the impurities to cling to a nearby surface. Consequently, ion generators often produce dirty spots on nearby walls and floors because they do not eliminate impurities; ion generators simply force impurities to cling to a surface (in the same way that static electricity can make a sock cling to a shirt). Ion generators are the second most popular type of air purifiers, but you won't find any ion generators or ozone generators for sale at AchooAllergy.combecause ion generators and ozone generators both emit ozone, a powerful lung irritant that is especially dangerous for people with asthma and other chronic lung diseases, children, and the elderly.

  • Charged Media Filters work the same way as electrostatic precipitators, but they collect particles on fiber filters instead of plates. The advantage of these filters is that they are able to collect very small particles, sometimes as small as 0.1 microns, through a combination of a filter and an electrostatic charge. The disadvantage is that, like the electrostatic precipitator filters, charged media filters lose their efficiency fairly quickly, and they can require more frequent filter replacements compared to a HEPA air purifier. These types of units can produce ozone, but the better ones on the market do not. If you are going to purchase this type of air purifier, make sure that it does not produce ozone. The best air purifier in this category is the Blueair air purifier.

  • Activated Carbon Filters are rarely used alone to purify the air, but they are often used in conjunction with other filters. Activated carbon and charcoal filters excel at adsorbing odors and gases and neutralizing smoke, chemicals, and fumes. "Adsorb" is not a typo; "adsorption" occurs when materials attach through chemical attraction. Activated carbon has been treated with oxygen, opening up millions of pores in the carbon. There are so many of these tiny pores that one pound of activated carbon has a surface area of 60 to 150 acres. This huge surface area makes it ideal for adsorbing gases and odors. These chemicals and gases are too small to be trapped by a HEPA filter, but they bond to the enormous surface area in the activated carbon. The bigger the carbon filter, the more chemicals it will be able to absorb and the longer it will keep on working. When it's full, it can't adsorb any more and has to be replaced. Impregnated carbon filters contain an additional chemical (a "chemisorbent") to eliminate certain chemicals like VOCs by rendering them harmless or trapping them within the filter media.

  • Antibacterial and Germicidal Filters eliminate bacteria and germs. The IQAir Clean Room HEPA air purifier, for example, utilizes a HEPA filter treated with agents to kill airborne microorganisms. Other air purifiers, like the AllerAir 5000 EXEC UV, Germ Guardian AC5000, and NQ Clarifier air purifiers, use a UV lamp to kill germs. NQ Clarifier air purifiers use either 2 or 4 UV lamps that claim single pass kill, which means microbes only have to pass by once and their DNA is altered to the point to where they cannot replicate. Air purifiers with UV filters are often used in sterile environments such as hospitals, kitchens, daycares, and labs. In residential use, they are great for controlling mold. If you are someone who gets sick often, an air purifier with a germicidal filter may be just what you need to give your immune system that extra boost.

  • Electrostatic Precipitators work on the same principle of electricity as ion generators and ozone generators, but electrostatic precipitators capture impurities rather than simply forcing them to cling to an external surface. Electrostatic precipitators use electronic cells to charge particles within the purifier and immediately trap the impurities on collector plates. The main advantage with this type of air purifier is that the collector plates never have to be replaced; they can be easily washed in the dishwasher. Be aware that some electrostatic precipitators also generate ozone.
  • Pre-Filters remove pet hair and other large particles prior to primary filtration and come with nearly all air purifiers. Most prefilters are either foam or some sort of non-woven nylon, and some have electrostatic properties to increase filtration. Look for prefilters with activated carbon. This type of prefilter will not only trap large particles but also adsorb odors and smoke. Regularly changing prefilters will increase the life span of your HEPA filter.

Air Purifier Technology

HEPA FiltrationThere are many types of air purifier technologies. HEPA filters remove 99.97% of all airborne particulates like pollen, dust, and animal dander. Many of the air cleaners we offer use activated carbon to remove chemicals and odors. Combining both a HEPA filter and a carbon filter provides the most effective air cleaning filtration.

Manufacturers vary on the technology used to clean the air we breathe. In addition to HEPA filters and granulated carbon filters, several manufacturers go a step further and use ultraviolet light. UV light can be used in addition to HEPA and carbon filter technologies to eradicate bacteria, viruses and mold spores. Some manufacturers implement pre-filters in conjunction with the other filter technologies mentioned above. Pre-filters extend the life of the HEPA filter and increase air cleaner efficiency by trapping larger particles before they get to the primary HEPA filter.

Additionally, manufacturers use electrostatic or electronic filtration technology. Electrostatic air cleaners use very small levels of positively and negatively charged particles to attract particles to collecting plates or filters. For example, airborne particles entering an air purifier are positively charged; and, the collection media is negatively charged causing the two to attract to one another. Manufacturers like Hunter and Blueair have ionizers built into their units, but these are optional features that are not primary to their air filtration process. Other units, like 3M air purifiers, rely solely on electrostatic filters as an inexpensive alternative to HEPA filters.

Another process used in air purification to clean the air is called ozone generation. We recommend avoiding this technology. We follow the Environmental Protection Agency's guidelines which state that ozone generators should not be sold as air cleaners. We do not sell, recommend, or endorse ozone generators. We recommend the best air purifiers based on your specific needs and your air cleaning goals. Whether you need allergen control, mold removal, odor removal, or asthma management, our job is to find the best air purifier for your unique situation.

Air Purifiers for Allergy Relief

HEPA filtrationAir purifiers help allergy sufferers by removing allergens in a room specific environment. We strongly recommend starting in the bedroom since people tend to spend more time in this room than any other in their house. Air purifiers only remove airborne contaminants and allergens. Particles that are heavier than air should be removed with a quality HEPA vacuum cleaner. Particles that are lighter than air include pollen, mold spores, animal dander and dust. These, as well as heavier dust mites and dust mite particulate, can be effectively filtered from the air in your home by using a quality air purifier. HEPA filters are essential for proper air filtration. A HEPA filter removes at least 99.97% of all particles as small as 0.3 microns, though many of the air purifiers you will find here filter particles as small as 0.1 microns with up to 99.99% efficiency.

Air Purifier Air Exchanges

A quality air purifier operates efficiently and quietly in a one room environment. To be effective, an air purifier must have a motor attached to a fan that draws air into the unit. Once the air is pulled into the unit, it is filtered through various types of filter media. Clean air is released back into the one room environment to start the cycle all over again. The amount of time it takes and air purifier to cycle through all of the air in a room is referred to an "air exchange."

The more air exchanges per hour, the better air quality in the room. The number of air exchanges is determined by two things: the cubic volume of a room and the cubic foot per minute (CFM) output of the air purifier. More air exchanges will result from a smaller room and a greater CFM output. Ideally, we would like to see between 4 and 6 air exchanges per hour. There is no such thing as overkill when talking about air exchanges. The more air moving through the unit; then, the more the air purifier will filter the air.

Air Purifiers Proper Placement

As a general rule, it is more difficult to filter the air in a large and open space (see the previous air exchanges section). Large living rooms and family areas, especially those with abnormally high ceilings, present a challenge to effective air filtration. Our rule with larger rooms is to attempt to direct the purified air exhaust from the air purifier to the vicinity of the rooms inhabitants. Many of the machines we sell have directional outflow registers. This allows the user to dictate where the clean air cycle begins and ends.
We suggest purchasing air purifiers for the bedroom first. Place the unit 6-10 feet from the headboard of the bed with the directional registers pointing at the bed. If the unit is too close, you will feel the draft from the unit. If the unit is too far away from the bed, the cleanest air from the air purifier will not be breathed. In the world of clean air, a smaller space is easier to effectively clean. This is one reason why we suggest starting in the bedroom. In addition to spending the majority of your life there, it is usually smaller than the other living areas of your home.

According to the majority of the air purifier manufacturers we work with, placing the unit near to where you are going to be is the norm. Ideally, place the unit between 5 and 10 feet from where you spend your time. Within the bedroom, the unit should be pulled out about a foot from the wall. We have debated if there is benefit to elevating the air purifier off the ground. In our opinion, it is not necessary. Gravity is pulling particulate down; and as it gets lower to the ground, the intake suction of the air purifier should pull the air and particulate towards the machine. Most air purifier manufacturers implement a bottom to top airflow--meaning the air is pulled into the machine at the bottom and released towards the top. Years ago when Honeywell made some of the only home air purifiers, their models pulled in from the top and exhausted downwards towards the floor. This system runs counter to the conventional wisdom of working with gravity to create air circulation. Fortunately their designs have changed for the better and other manufacturers have followed and further innovated with better air flow circulation in mind.

Air Purifiers Performance and Limitations

Air purifiers will not perform miracles. Quality air purifiers create an air cycle in a one room environment and filter that air through quality filter media. The filter media is usually HEPA cloth, carbon, or a combination of the two. Ideally the machine will filter the entire volume of air in the room 4-6 times per hour.

The effectiveness of an air purifier varies on two things: the sensitivity and severity to the allergen the user is trying to reduce exposure to and the relative strength of the contaminant or pollutant.

One of the easiest particulates to filter from the air is dust. Dust is abundant and omnipresent. Some of the hardest airborne particulates to filter are cat dander and toxic chemicals. Cat dander sticks easily to fabrics and stays aloft for a long time. If a cat allergy sufferer wants to try an air purifier, we suggest they start by placing a unit in their bedroom and exercising limited source control. Politely and lovingly, keep the cat (the source of the dander) out of the bedroom.

When selecting an air purifier, looks for models with sealed systems. These air purifiers usually have seals or gaskets around the filters to help keep dirty air from mixing from clean air. Most air purifiers come with some sort seal or the filters are designed with a material that ensures no air leakage.

Many fumes and toxic chemicals fall outside the adsorption spectrum of the majority of filter media. To filter out a wider range of chemicals and gases, air purifier manufacturers introduce different types of media. Highly adsorptive carbon has an extremely large surface area to size ratio. This characteristic helps carbon trap particulates. Other similarly porous derivatives, like potassium permanganate, potassium iodide, alumina and zeolite, are also used. Potassium permanganate is an oxidizing agent that does not generate toxic byproducts.

Two other uses of potassium permanganate include: being used as a disinfectant for treating humans and animals, and being used to clean and filter well and waste water. Zeolite also has a micro porous structure. The name is derived from the Greek word which means stone that boils. Zeolite forms naturally where volcanic rock and ash layers react. Natural zeolites often are excluded from commercial applications. Zeolites are widely used in both domestic and commercial water purification as well as air purification.

Air Purifiers Fans and Motors

A question we field multiple times per day is, Should I leave my air purifier on all the time? The answer is an emphatic Yes! (Unless there is an unusual circumstance like you are leaving on a 3 month vacation). Air purifier motors are quiet, very energy efficient, do not consume a large amount of electricity, do not get hot, and easily maintain a constant RPM. An air purifier can not clean the air if it is not turned on. In fact, we recommend turning your air purifier on its highest setting when you are away. This promotes maximum CFM output and air exchanges per hour. The highest fan speed setting is usually too loud to tolerate when you are in the room, which is why we suggest running it on the highest setting when you are absent from the room.

Air Purifiers Benefits vs. Side Effects

Air Purifier Benefits vs. Side EffectsSome of the many benefits of using an air purifier in your home or office include: breathing less contaminated air, keeping your allergen load below its reactionary threshold, sleeping and breathing better, and living healthier naturally. The side effects of using an air purifier are very small: energy cost (similar to the use of a 60w light bulb) and white noise. Actually, most people unknowingly benefit from the white noise from air purifiers. White noise drowns out distracting background noises that can interrupt sleep. White noise also helps people relax. For these reasons, white noise is used widely in sleep centers throughout the country.

Wash or Replace Pre-Filters

A debated subject in our company is whether you should wash or replace pre-filter media? It is a personal decision. Pre-filters capture the large particles and need to be replaced more frequently. Some people do not mind ordering a few extra filters and simply throwing away the old filters when it is time to replace. Other people have no problem removing the old pre-filter, vacuuming it or rinsing it through water, and allowing it to dry thoroughly before replacement. With activated carbon prefilters, you can use them beyond the recommended 3-6 months, but generally after this time period, they have adsorbed as many odor or smoke molecules as they can hold with their limited amount of carbon. So while cleaning them will extend their large particle trapping capabilities, most smoke or odor adsorption will have ceased. There is some flexibility in this, so either cleaning, to extend the life, or replacing boils down to a personal decision.

Beware of Scams and False Advertising

As the case with many industries, there are good guys and bad guys. According to the EPA as well as Consumer Reports, many manufacturers falsely advertise that ozone cleaners are air cleaners. This is false. There is actually a consumer alert out issued by the EPA. The bottom line is ozone generators do not clean the air. They charge the air using electricity which makes molecules generally heavier so they fall to the ground. Our concern, as well as the Environmental Protection Agency's and Consumer Reports, is that ozone generators do just that; they generate ozone. Ozone is a harmful lung irritant. Another name for an ozone generator is an electrostatic precipitator. Buyer beware, if it sounds too good to be true, then it probably is. Again, air purifiers will not perform miracles. Many bars and restaurants use ozone generators, because they claim to help with alleviating cigarette and cigar smoke. We have no proof that this claim is true. Ozone is a concern because it is a threat to users. There is currently no standard for acceptable ozone levels.

Other Factors to Consider Before Buying an Air Purifier

Area Coverage
Make sure the square footage listed for the air purifier is about the same or slightly greater than the square footage of the room where you intend to use it.
Air Changes Per Hour (ACH) This number, also known as the ACH rating, tells us how frequently the air purifier can exchange all the air in a given room. For example, if the purifier has a ACH rating of 6 for a 20' x 20' room, then it is capable of exchanging all of the air in that room 6 times every hour. If you have allergies or asthma, you want an ACH rating of at least 4 and preferably 6 or 8.
Clean Air Delivery Rate (CADR) The CADR, calculated by AHAM (The Association of Home Appliance Manufacturers), tells us not only how much air is purified, but also how well it is purified. Air purifiers that have been tested by AHAM should have the AHAM Certified seal and CADR numbers for three pollutants: tobacco smoke, pollen, and dust. The higher the CADR rating, the more effective the air purifier is against that pollutant. CADR ratings are calculated impartially and recognized by the Environmental Protection Agency and American Lung Association.
Price Our air purifiers range from affordable air purifiers for small spaces to fully loaded air purifiers for large rooms.
Filter Replacements If you are buying a HEPA filter, don't forget to check and see how much replacement filters will cost. If your unit includes both a HEPA filter and a carbon filter or other combination filtration media, they will probably need to be replaced separately, and may last for different periods of time. This can be a hassle, particularly if they are difficult to access. Luckily, you can take the hassle out of replacing your filters with our Filter Replacement Program.
Noise Level Some air purifiers, like our Blueair units, are extremely quiet while others can be quite loud when operating at high power. For most units, the slower the air is passing through the filter, the more effective the filter is. So while some units are louder when set to high, they are quieter and offer better filtration at lower fan speed settings. If possible, ask for a demonstration before you buy your air purifier. If you live near the Atlanta area, we'd be glad to give you a demonstration in our showroom.
Energy Usage Like all appliances, different air purifiers use different amounts of energy for operation. Unlike most appliances, air purifiers run continuously, so you'll want to consider your utility bill before buying an air purifier. If only volts and amps are listed, simply multiply the two: volts x amps = watts. Typical mechanical air filters can use anywhere from 50 watts on low to 200 watts on high. (For comparison sake, a typical lamp uses about 60 watts, while a typical computer uses about 365 watts).

Air Pollution Some air purifiers pollute the air with ozone, a powerful lung irritant that is especially dangerous for asthmatics, children, and the elderly. does not sell either ozone generators or ion generators because they both emit ozone. They are not effective air purifiers.

Extra Features These are the bells and whistles. They can make your air purifier a lot easier to use. On the other hand, they can also significantly up the price on an air purifier that isn't really all that much better than the next one. You simply have to decide which features will make your life easier and which ones are not simply worth the extra cash. For example, a filter change indicator light lets you know when to change the filter, and handles or casters are important if you plan on moving your air purifier around a lot.

Manufacturer's Reputation A manufacturer's reputation and the experiences of past customers deserve consideration in your decision. Certain manufacturers and products are highly respected in the industry for a reasonand the same goes for products which have garnered less respect.


Warranty - An Austin Air air purifier comes with a five-year warranty. Another manufacturer called AllerAir offers a ten-year warranty. Be sure to consider what the warranty coversmotor, fan, electrical components? Also, find out if certain customer actions will void the warranty. Some manufacturers will void the warranty if the customer does not purchase replacement filters over the recommended time period. This stipulation can be inconvenient if you plan to run your unit less often or if the air in your home is cleaner than average.

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