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Air Purifier Buying Guide

HEPA Air Purifier Buying Guide
Tightly Sealed, Modern Homes Trap Indoor Air Pollution Often Creating Worse Air Quality Than Outdoor AirQuality air purifiers have never been more important for good health. The tight seals that make your home comfortable and energy efficient also trap indoor air pollution. From cooking fumes and cleaning vapors to dust and pet dander, there is a wide variety of vapors and particles that pollute indoor air. Statistics from the Center for Disease Control (CDC) and Environmental Protection Agency (EPA) have shown that the air inside your home can be five to ten times dirtier than the air outside, and more importantly, Americans spend an average of 90% of their lives indoors.

So you decided you want to do something about this and begin searching. Shopping for the right air purifier can be confusing and frustrating. Some air purifiers on the market actually pollute the air with harmful levels of ozone, a powerful lung irritant that can be especially dangerous to asthma sufferers. Many are marketed as inexpensive and use language that makes the air purifier appear to be something that it is not. Others will provide filtration or air flow rates rates based on theoretical results, not actual testing or usage. Others still can simply confuse you with the sheer number of options, sizes and prices available, and leave you feeling just as overwhelmed as when you first began your search. No matter the brand, price or style of air purifier you are searching for, there are key things to look for with any air purifier. 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 first 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, mold spores, dust mite allergen, pollen, plant spores, and fungi, and they are the most common cause of indoor allergy and asthma attacks. A HEPA air purifier is the best method of eliminating most airborne allergens. Here is a look at the average particle size of some of the most common indoor airborne particles:Common Household Air Pollutants
  • Tobacco or Wood Smoke was traditionally a very common indoor air pollutant. Over the years, smoking rates have fallen dramatically, and the number of people who still heat their home with wood is lower than at any other point. So while these remain powerful indoor irritants, they are becoming less frequently found.
  • Household Odors and Gases include cooking odors, kitty litter, various toxins, and gaseous pollutants like indoor pesticides, aerosols, and chemical cleaners. This type of pollutant is far more common than it used to be. Activated carbon or charcoal 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 to a substance, in this case carbon, 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. Like chemical cleaner vapors and aerosols, these too are more prevalent than they have been in the past.
  • 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

Air Purifier Buying Guide - Different Types of Air Filtration and PurificationDifferent air purifier filters target different types of air pollution, and what they target depends almost exclusively on the type of filtration technology they employ. HEPA air purifiers are the most popular, and they are perfect for eliminating household allergens such as dust, animal dander, pollen, and other particulate. They are not very good at capturing ultra-fine particles like viruses or eliminating foul odors, organic compounds, smoke, or chemical fumes. 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, pollen, and dander as well as things like smoke, odors, and chemical vapors. 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:

  • Best for Particle Filtration - HEPA FilterHEPA (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.** This U.S. HEPA standard was 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 for all common particle allergens. However, not all HEPA filters are created equal. Size matters: the more square feet of HEPA filter, the more particulate 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, Air Pura, NQ Clarifier, Amaircare, Germ Guardian, and Whirlpool.

  • Best for Odor & Smoke Filtration - Activated Carbon/Charcoal FilterActivated Carbon Filters are rarely used alone to purify the air, but they are often used in conjunction with other filters. Activated carbon/charcoal filters excel at adsorbing odors and gases and neutralizing smoke, chemicals, and fumes. When carbon is treated with oxygen, it opens up millions of pores. There are so many of these tiny pores and fissures 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, providing an enormous surface area for potential bonding with chemical/vapor molecules. The larger the carbon filter, the more chemicals it will be able to absorb and the longer it will keep on working. When it's full, when it can adsorb no more chemical molecules, it has to be replaced. Impregnated carbon filters contain an additional chemical (a "chemisorbent"), that often either broadens the range of chemicals the carbon will filter or allows for more targeted filtration of a specific type or family of chemicals pollutants.
  • Better Than HEPA Filtration? Electrostatic Air Purifier FiltersCharged Media Filters are a combination of two technologies, a particle filter (similar but nowhere near as efficient as HEPA) and a slight electrostatic charge. This charge acts the same way that static cling causes your socks to stick together out of the dryer. The advantage of these filters is that they are able to collect very small particles, sometimes as small as 0.1 microns, and that for a period of time, they are extremely effective. 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. 3M Filtrete air purifiers use this filter technology.A variation of this uses a small metal filament that allows electrical current to pass thought it and charge particles as they pass through. These now charged ions attract and cling to the particle filters. These types of units can produce ozone, but the better ones on the market do not. The best air purifier in this category is the Blueair air purifier (no ozone). Both versions of charged media filters can actually yield filtration rates that EXCEED HEPA standards.
  • Not As Advertised - Electrostatic PrecipitatorsElectrostatic Precipitators work off of similar principles of charged media filters, but instead of capturing these now charged particles on filters, the instead precipitate out and adhere to collector plates. This is the type of technology that was behind the infamous Ionic Breeze, and that "air purifier" highlights two problems with this type of filtration. First, air flow is critical, and if not robust, it is simply recycling the same air over and over. Secondly, older and cheaper versions of this technology will actually emit ozone. The big advantages are that the collector plates never have to be replaced; they can be easily washed in the dishwasher. This type of unit is also very quiet. At this point, these models have largely fallen out of favor.
  • The Worst 'Solutions' To Cleaner Air - Ozone GeneratorsIon 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. Ion generators were traditionally the second most popular type of air purifier, but you won't find any ion generators or ozone generators for sale at AchooAllergy.com because both emit ozone, a powerful lung irritant that is especially dangerous for people with asthma and other chronic lung diseases, children, and the elderly. This type of filtration has largely fallen out of favor with most manufacturers, but some people will still use those to "ozone shock" rooms, for their efficacy in killing pathogens and mold.
  • Germicidal Air Purifier Filters & UV Light - Destroy Pathogens & MicrobesAntibacterial and Germicidal Filters eliminate bacteria and germs. Air purifiers, such as the AirPura UV600, 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 or UV lamp may be just what you need to give your immune system that extra boost.
  • Photocatalytic Oxidation - A New Way to Remove VOCs?Photocatalytic Oxidation (PCO) is a new type of filtration technology. There are two components to this type of filter. A metal plate coated in titanium dioxide attracts works in conjunction with UV light to actually oxidize chemicals. The titanium dioxide and UV light physically break down the molecular bonds that hold large molecules of VOCs together. In doing so, a large VOC molecule can be oxidized more with each pass with the end result being carbon dioxide and water molecules. The long term efficacy of PCO is still being researched. While it is effective in oxidizing VOCs, long strand chemicals can take several passes to full oxidize, so as a large compound breaks apart, it can actually increase the amount of a smaller derivative compound in the air, at least temporarily. Still new and not widely researched, photocatalytic oxidation is employed by a handful of air purifier manufacturers.
  • Prefilters - Basic But EffectivePre-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 polyester, 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 the other particle filters in the air purifier.
  • Heat is a newer entry among the filtration types. Technically, it's not a filter as the rest of these are. It's more in line with UV as a mode of filtration. Currently very, very few air cleaners use heat, but the Airfree is an example of a unit that uses it best. An inner ceramic core heats up to nearly 400°. As the warmed air rises out of the machine, cooler in enters to replace it. Organic particles, like bacteria, viruses, mold, and dust mites are literally incinerated by the heat. The air passes through a cooling chamber then out the machine. The drawbacks with this are two-fold. First, it's a slow process. There is no fan, so this type of unit relies upon convection currents. It can take 3-7 days before a room will begin to show a dramatic drop in particles. The second drawback is this type technology only effects biologicals (bacteria, viruses, mold, dust mites - living things). Chemical vapors, smoke, and fragrance are largely unaffected. A unit with this type of filtration is better referred to as an air sanitizer or air sterilizer, particularly since "purification" is so tightly linked to filtration.

** Why 0.3 microns, and why do you now see PM2.5? 0.3 microns is what has been determined to be the Most Penetrating Particle size. In terms of a HEPA filter, 0.3 microns is the Most Penetrating Particle size because it penetrates or passes through HEPA filter media the easiest - it's the hardest particle to trap. HEPA filters trap particles by one or a combination of three mechanisms, impaction, interception, and diffusion. Particles that are 0.4 microns or larger are often snared by impaction or interception while diffusion is what traps most particles 0.1 microns or smaller. This leaves a gap, right around the 0.3 microns, where filtration becomes extremely difficult, and thus, the weak point of the filtration spectrum. Much like the weakest link of a chain, a HEPA filter is only as good as its weakest point of filtration, and that is 0.3 microns.

PM2.5 is a slightly broader classification of particles. These are considered fine particles and includes all particles that are 2.5 microns or smaller in size. As a subset of particles, PM2.5 is often used as a reference point since this subset penetrates the deepest into the respiratory system.

Air Purifiers for Allergy Relief

Air Purifier Replacement HEPA FiltersAir purifiers help allergy sufferers by removing allergens in a specific environment, whether that is your home, office, or dorm. In the home, we strongly recommend starting in the bedroom since people tend to spend more time in this room than any other in their house. Starting in the bedroom allows you to create an allergy friendly environment for yourself, and a space where you can get a good night's rest. Air purifiers only remove airborne contaminants and allergens. Particles that are heavier will precipitate out of the air and settle on furniture and flooring, which means to make your bedroom truly allergy friendly, an air purifier is only a good first step. Now that you know where to start, what other things are there to consider before you buy?

Air Purifier Air Exchanges

Most quality air purifiers operate efficiently and quietly in a one room environment. To be effective, an air purifier must have a motor and fan powerful enough to properly circulate air throughout the space. Once the air is pulled into the unit, it is filtered through various types of filter media, and clean air is released back into the one room environment to start the cycle all over again. The amount of time it takes an air purifier to cycle through all of the air in a room is referred to as an "air exchange."

The more air exchanges per hour (ACH), the better air quality in the room. The number of air exchanges is determined by two things: the cubic feet (volume) of a room and the cubic foot per minute (CFM) output of the air purifier. All air purifier manufacturers list airflow ratings (in CFM) for each fan setting at which their machine operates. Ideally, you want to set a goal of 4 to 6 air exchanges per hour. There is no such thing as overkill when talking about air exchanges.

Proper Placement of an Air Purifier

As a general rule, it is more difficult to filter the air in a large and open space, and this is mainly due to inadequate air circulation. 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. Inside a room, be sure to keep adequate space around the air purifier, typically 18" or more. Most units intake air from multiple sides, and restricting this by placing the air purifier against a wall or piece of furniture will reduce efficiency.

In the bedroom, place the unit 6-10 feet from the headboard of the bed with the directional registers pointing at the bed. This is often far enough away to avoid feeling a draft but close enough that cleaned air is reaching you.

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, and 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, but they can go a long way in reducing allergens and irritants in the home, while improving indoor air quality. The effectiveness of an air purifier varies along several factors. You specific sensitivity or the severity of your reaction to the offending allergen, the source and concentration of these irritants in the home, and the type of air purifier being used.

HEPA Filters - The Key to Better Indoor AirOne of the easiest particulates to filter from the air is dust. Dust is abundant and omnipresent, but these particles tend to range from visible (which are generally filtered by your body before they can reach the lungs) to 10 microns (effectively filtered by a HEPA air purifier). Some of the hardest airborne particulates to filter are cat dander and toxic chemicals. Cat dander is extremely small, and can stay aloft quite some time. In fact it is one of the smallest, common indoor allergens. This type of dander is also "sticky". Once it does land, it adheres easily to fabrics, walls, and flooring. This means if you've just moved into a home that used to have a cat, to you, it may still feel as if the cat is there! For those who are actually allergic to their beloved pet, things can be even more difficult. While there are a variety of things you can do to mitigate the allergen, using a HEPA air purifier in the bedroom and keeping the cat out of that room can go a long ways to keeping your allergies at bay.

Another factor that can impact air purifier performance and efficiency is whether or not it has a sealed system. A sealed system generally refers to a series of seals or gaskets that ensures that once air enters the air purifier it does not leave the machine until it has passed through the filters. For those coping with moderate to severe allergies, a sealed system machine is one that should strongly be considered.

One of the biggest performance problems isn't actually a problem with the performance of the air purifier. It's often the result of a mismatch between what type of filtration is needed and what type of filtration is being used. Odors, perfumes, smoke, and chemical vapors will largely pass right through a HEPA air purifier, and even units with a carbon prefilter often contain so little carbon that they cannot adequately filter these pollutants. Large activated carbon filters are often the best way to solve this problem.

This highly adsorptive substance has an extremely large surface area to size ratio, and it is this characteristic, combined with chemical properties of carbon that make it ideal for trapping odors, smoke and vapor pollution. For more specific filtration of VOCs consider carbon that has been blended with other materials, like potassium permanganate, potassium iodide, alumina and zeolite. These substances can broaden the chemical filtration range of carbon or oxidize VOCs. Paring the right filter media for your needs is kep to getting the performance you want from your air purifier.

Air Purifier Fans, Motors, and Usage

Should you 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 generally quiet on low to medium speeds, very energy efficient, do not output much noticeable warmth, and easily maintain a constant RPM. The fact remains, an air purifier cannot 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. The highest fan speed setting is usually too loud to tolerate when you are in the room, which is why we often suggest running it on the highest setting when you are absent from the room. Upon returning, turn the fan speed down to a more comfortable level. As a final note, every HEPA air purifier is likely to be "loud" when used on its highest setting. Any unit worth the money you spent on it must be able to properly circulate air throughout the room, and this relies on a fan.

Air Purifiers Benefits vs. Side Effects

Air Purifier Buying Guide - 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 without additional pharmaceuticals or a radical lifestyle change. The side effects of using an air purifier are very small: energy cost (average to the cost to use 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, and for many, white noise can actually be relaxing. For these reasons, white noise is actually 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 often a personal decision. Pre-filters capture the large particles and often 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 with water, and allowing it to dry thoroughly, and repeating this process a couple times before actually replacing the filter. 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 in most cases, cleaning and reusing prefilters or simply replacing them boils down to a personal decision.

Beware of Scams and False Advertising

As the case with many industries, there are good guys, bad guys, and some in between. In the past, there was a very good example of the problems within this industry. According to the EPA as well as Consumer Reports, many manufacturers were falsely advertising that ozone cleaners were air cleaners. This was, and is, false. Resellers and dealers go with what information is provided to them and at the time, there was little information out about how this type of machine could negatively effect health. Even after more information came to light, many continued to manufacture and electrostatic precipitators are rarely seen for residential use.

More recently, many people will recall the Ionic Breeze by Sharper Image. This air purifier made amazing claims, required no filters, and used no fans. One class action lawsuit later, and we all discovered that not only did this air purifier not work, but it was actually producing ozone.

Buyer beware, if it sounds too good to be true, then it probably is. Again, air purifiers will not perform miracles, and there is never a short of dubious people out there who continually try to make a quick buck from duping another.

Air Purifier Buying Guide - Summary of Factors to Consider


How Much Area Does The Air Purifier Clean
Coverage Area
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. Square footage numbers are calculated based on an 8' ceiling, CFM, and a stated number of air exchanges per hour.

Air Exchanges per Hour Are A Good Indicator of Air Purifier Efficiency
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.

How Much Does An Air Purifier Cost?
HEPA air purifiers range from affordable air purifiers for small spaces to fully loaded air purifiers for large rooms. Initial cost isn't the only expense related to operating an air purifier. Also consider how much replacement filters will cost annually. For some energy usage may also be a concern. While most use little energy, some are Energy Star rated.

Replacement Filters Can Largely Determine Annual Operating Costs
Filter Replacements
If you are buying a HEPA air purifier, 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 may need to be replaced separately and after different periods of time. Regular filter replacement is key to getting to the most of your investment while minimizing wear on the motor. Additionally, some manufacturers require regular filter replacement as a condition of their warranty.

Energy Usage Can Effect the Cost to Own & Use An Air Purifier
Energy Usage
Like all appliances, different air purifiers use different amounts of energy. Unlike most appliances though, air purifiers run, or should run, continuously, so you may 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. And to determine how many kilowatt hours your model uses per day, multiple watt x hours then divide that by 1000. This will give you daily kilowatt hour usage. Typical air cleaners 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 300 watts).

Fan Speeds & Noise of an Air Purifier
Noise Level
Some air purifiers, like Blueair and AirPura, are extremely quiet while nearly all can be quite loud when operating at full power. For models with thick carbon filters, a slower fan speed can actually produce better filtration results. A fan moving too slowly may not be pushing enough air to properly clean the room. It can be a bit of a balancing act when it comes to noise, but in general, there are appropriate fan settings with comfortable noise levels on all air purifiers. 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.

Clean Air Delivery Rate (CADR)
Despite flaws with the CADR, this test can give results to help compare air purifiers. While not all manufacturers submit their products for testing, the CADR can be helpful with an apples to apples comparison between models.

No Ozone Air Purifiers
Air Pollution
Some air purifiers pollute the air with ozone, a powerful lung irritant that is especially dangerous for asthmatics, children, and the elderly. Avoid these. Look for air purifiers that are CARB certified (California Air Resource Board). CARB is the most stringent testing agency of consumer products, and if you're unsure, just ask!

Additional Accessories and Features
Extra Features
These are the bells and whistles. They can make your air purifier a lot easier to use or simply be an added expense that seem useful but really aren't. This is a bit of a balancing act. 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 frequently. What about audible reminders, LCD screens, or backlights?

Manufacturer's Reputation
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 reason and the same goes for products which have garnered less respect. Some have been around for decades, and while others may be new, they can still have merit.

Air Purifier Warranties Vary
An Austin Air air purifier comes with a five-year warranty. This is fairly standard. One offers a lifetime warranty, and many of the less expensive models offer only 1-3 years. Be sure to consider what the warranty covers, motor, 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.

Ready to buy? Shop all air purifiers or visit our Air Purifier FAQs.