Air Purifier Buying Guide: Choosing the right air purifier to suit your needs

With all the acronyms and jargon in the air purifier industry, choosing the best air purifier is pretty confusing for the average person.  Not to worry – we are here to provide a neutral and informational guide as to the air purifier best designed for you.  Air purifiers can remove a number of airborne irritants, including mold spores, dust, pollen, odors, noxious fumes, bacteria, viruses, pet dander, and more.  However, all of these substances require different strategies since there are so many different shapes and sizes of particles to deal with. 

This guide will show you where to start in terms of finding a machine with the proper filter types, as well as one that is powerful enough to clean whatever size area you need.  The latter half of the guide is a summary of what to look for depending on the type of substance you wish to remove from the air, as well as links to our top picks.  We will also provide examples of quiet air purifiers, which is a common concern.

Quick Links

Important Air Purifier Acronyms and Terms
How Air Purifiers Work and The Different Types
Noise Level and Additional Considerations
Choosing the Right Air Purifier
       Choosing an All-Around Air Purifier
       Choosing an Air Purifier for Allergies
       Choosing an Air Purifier for Asthma
       Choosing an Air Purifier for Mold
       Choosing an Air Purifier for Pet Dander
       Choosing an Air Purifier for Microorganisms
       Choosing an Air Purifier for VOCs
       Choosing an Air Purifier for Smoke Odor
Top Picks by Category

Air Purifier Terms and Concepts

Before you start looking at different features and specifications, it will help to have heard some of the vocabulary and acronyms that go into describing an air purifier’s features and capabilities.  The most important ones are CADR, ACH, and CFM.  Here are the terms you will want to know:

Particulates:  For our purposes, this generally just means small airborne particles.  Odors, such as smoke, are often described differently since these particles are much smaller than dust, mold spores, pollen, and pet dander.

HEPA Filter:  High Efficiency Particulate Arresting or High Efficiency Particulate Air – A HEPA filter utilizes a thick mat of randomly arranged fibers of varying thickness.  In order to be classified as true HEPA by the U.S. Department of Energy, the filter must be able to 99.97% of airborne particles larger than .3 microns that pass through it.  HEPA filters are good for capturing dust, pollen, mold spores, pet dander, and a variety of other allergens.

VOC Filter:  VOC filters contain compounds designed to trap and remove smoke odor and other fumes from your home.  Examples are potassium permanganate and Zeolite – these are porous compounds that adsorb odor particles, which tend to be the smallest of all particles we are looking to get rid of.  You will need a machine with a VOC filter if you want to get rid of pet odor, smoke smell, and other noxious fumes.  Adsorption is the adherence of ions or molecules from a liquid, gas, or dissolved solid to a surface.  An activated Carbon filter is a VOC filter.

CADR:  Clean Air Delivery Rate – In short, it is the capacity of a machine to deliver clean air.  The higher the number, the more powerfully the machine cleans the air.  In long, it is the measure of how much particulate of a certain size range has been removed from a standard room (chosen to be 1008 cubic feet) above the rate at which these particles would naturally settle out of the air.  Because different sized particles settle out or are filtered out at different rates, CADR is given in three variants: dust, tobacco smoke, and pollen, since these particles range from a fraction of 1 micron to around a dozen microns.  CADR ratings are intended for residential areas, such as specific rooms or apartments.  For a given room, it is recommended that the filter’s CADR rating for smoke multiplied by 12 is equal to or greater than the volume of the room in cubic feet.  As you can see, the CADR relies on several variables and assumptions, which is why some manufacturers (like Airgle) don’t use it to define the capacity of their air purifiers.  CFM is a measure that we see more often.

Micron:  A micron is 1/1000 of a millimeter, or one one-millionth of a meter.  For reference, a typical human cell is about 20 microns across; human hair ranges from several dozen to several hundred microns in width.  Most allergens and bacteria are larger than 1 micron in size, though smoke and some dust particles come in fractions of microns.
Pollen, mold spores, and pet dander particles are typically in the tens of microns.  The micron is the standard unit of measure when describing air purifier filters and the particulates they are capable of filtering from the air.

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CFM:  Cubic Feet per Minute – This is a measure of airflow through a machine.  This is influenced by the air purifier’s fan speed, air flow within the room, furniture present, and how saturated the air is with particulates.  A higher CFM means a more powerful air cleaning.  To calculate your desired CFM, take the cubic volume of the room (square footage times ceiling height) and multiply it by the ACH you want; then, divide by 60 to reach the CFM.

ACH:  Air Changes per Hour – How many times per hour all of the air in the room is filtered.  2 ACH is acceptable for standard use in a relatively clean home, but we recommend at least 5 for those with chronic allergy or asthma symptoms or respiratory sensitivities.  The higher, the better.  Note that Air Changes per Hour is dependent on the size of the room and the CFM capacity of the machine, so no air purifier has a certain “ACH Rating.”  A machine will deliver different ACH performance depending on the size of the room in which you place it.

VOCs:  Volatile Organic Compounds – These are organic chemical compounds with relatively high vapor pressures, meaning they evaporate into the air easily.  Examples of VOCs include acetone, benzene, ethylene glycol, methylene chloride, toluene, xylene, hexane, and more.  These chemicals are a lot more prevalent in your home than you think; they are found in adhesives, wood products, paints, solvents, pesticides, fabrics, caulk and sealants, varnishes, cosmetics, cleaning chemicals, air fresheners, markers, nail polish remover, and newspapers.  They are also produced by fireplaces, stovetop cooking, smoking, printers and photocopiers, and other daily activities – here is a breakdown from the EPA.

MCS:  Multiple Chemical Sensitivity – Intolerance to the low-level exposure of chemicals/VOCs.  Symptoms of MCS include nausea, fatigue, headaches, and lightheadedness. 

AHAM:  Association of Home Appliance Manufacturers – An organization that has created many standards for air purifier and dehumidifier ratings, including CADR.

Energy Star Certified:  Some air purifiers are Energy Star Certified, meaning they are more energy efficient and will save you around $25 per year.  However, air purifiers generally don’t need a whole lot of energy to run.

Pre-Filters:  Pre-filters are a great way to extend the longevity of HEPA filter and make replacement less frequent.  A pre-filter traps larger particles, such as hair and pet dander.  This ensures that your HEPA filter, which is specially designed to trap extremely small particles, doesn’t get clogged with large irritants that are relatively easy to catch.

How Do Air Purifiers Work? - The Different Types  

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There are many different ways to remove unwanted airborne particles, and this section will explain the physics behind the different configurations.  Typically, these machines work by sucking air in through a fan and passing it through a medium, most commonly a HEPA filter.  However, some air purifiers don’t use filters at all.  The best type of air purifier for you depends on what kind of particles you are trying to filter out, how you want it done, and how often you are willing to clean collector plates or replace air filters.  For related information, see our article entitled Do Air Purifiers Work?

HEPA Air Purifiers:  Both our and the general community’s consensus pick for the best type of air purifier in terms of its performance versus the byproducts they produce.  These do not produce ozone like the machines outlined below.  HEPA air purifiers use very high-quality filters to trap particulates.  Additionally, many air purifiers couple HEPA filters with VOC filters; the combination of these filters will cover most particles, allergens, fumes, and odors.  All in all, we think that HEPA air purifiers represent  the safest and most complete type of air purifier, although there are hundreds of these to choose from, which is a task in itself.  Here is a general diagram of a HEPA filter.

Ozone Generators:  Ion generators and ozone generators emit charged particles into the air, which attach to particulates like dust and mold spores.  This causes them to either fall to the floor or cling to nearby surfaces, such as walls or furniture.  Thus, these aren’t the best choice since they don’t actually trap the particles you are trying to remove from your home.  Furthermore, these machines emit ozone, which is a harmful lung irritant that is especially dangerous for people with respiratory sensitivities like asthma.

Electrostatic Precipitators:  These work via the same principle as ozone and ion generators, but the attachment of the ions occurs within the machine itself, meaning the particles are actually trapped.  The collector plates can be washed and do not have to be replaced.  Unfortunately, electrostatic precipitators also produce ozone.  These are also called air ionizers.

Air Sanitizers: Air sanitizers, or air sterilizers, specialize in the removal of biological particulates, such as viruses, bacteria, and spores.  These machines typically use heat or UV light to kill or destroy pollen, dust mites, mold, fungi, and germs.  Airfree air sterilizers are a good example. Air sterilizers are generally very quiet and do not have a filter to replace. 

Fundamental Considerations                                                  

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Besides the CFM and ACH that we mentioned above, here are the other important things to look into.

Square Footage:  Most air purifiers will have a recommended room square footage somewhere in the description.  This figure is calculated based on the machine’s CADR or CFM and an arbitrary ACH.  A good rule of thumb is to choose an air purifier with a square footage a bit higher than that of the room or area in which you would like to place it.  Sizes range from portable units to single-room air purifiers to whole-house air purifiers.  Some machines are designed to both stand alone or install and integrate with your A/C system.

Noise Level:  Many people ask us about the best quiet air purifiers.  Generally speaking, a machine’s cleaning power (in CFM) is inversely proportional with how loud it is.  However, new technologically has made it possible to provide powerful performance along with quiet operation.  Airfree air sterilizers are nearly silent.  Many manufacturers have models with variable speed control, meaning you can set the fan speed and, in turn, manage the noise level.  Look for one of these if you prefer to have a quiet machine when you’re at home that you can set to full speed when you are out of the house. 

Some manufacturers will provide the operating noise level of their machines in decibels.  Generally, decibel levels in the fifties are pretty quiet for an air purifier, with the quietest air purifiers capable of operating in the low to mid thirties.  This chart will give you a reference guide as to the noise level of an air purifier -

http://www.gcaudio.com/resources/howtos/loudness.html

Monitoring & Automation Features:  Besides variable fan speed control, there are a few other convenient features that some air purifiers have.  This includes a servicing or filter change indicator, which will tell you when it’s time to replace the filter (or wash the collection plates, in the case of an electrostatic precipitator).  Some models have air quality sensors/monitors which are designed to detect the pollution level in the room and automatically adjust fan speed accordingly; however, this technology has not been perfected yet.  Another feature some models have is an automatic timer, allowing you to set the machine to run or turn off at appropriate times.

Energy Consumption:  Since most today’s models are very efficient machines by design, we do not consider energy consumption to be a significant factor in choosing an air purifier.  However, there are certain Energy Star rated models which will save you around $25 per year in energy costs depending on how powerful it is and how often you run it.

Filter Replacement:  HEPA filters are more expensive than you might think, so you may want to look up prices for replacement air filters compatible with the model you want.  The good thing is that HEPA filters will generally last for over a year, often for around three years depending on the indoor pollution level.  Pre-Filters require replacement far more often but are much cheaper than HEPA filters.  VOC filter replacement is generally between Pre-Filter replacement frequency and HEPA filter replacement frequency.  Though filter replacement is a relatively infrequent requirement, it is a cost you may want to consider before making your selection.

How to Choose an Air Purifier

Before you start looking for the best air purifier for you and your family, be sure to have read through the information we provided earlier in this guide regarding CADR, CFM, and ACH. 

There is a huge number of ways in which an air purifier can clean air, but the strategy for attacking certain irritants differs across the board.  Someone with seasonal allergies will need to look for a different type of machine than a person with MCS.  The following section will explain the most basic features to look for in an air purifier based on the substance or substances you wish to remove from the air.  We will discuss all-around air purifiers, asthma air purifiers, allergy air purifiers, and targeting specific types of particulate. 
                                                                                                                                                                                                                                                                                                                                       

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Choosing an All-Around Air Purifier:
In practice, many of the categories for which people search for air purifiers involves some sort of allergy, whether it is pollen, dust, mold, or pet dander.  For these allergens, most standard HEPA filters will do the trick.  However, some people are simply looking to increase indoor air quality overall.  Air purification becomes slightly more challenging when you are also looking to get rid of VOCs, bacteria, fumes, and odors.  This is because many of these particles come in the fractions of microns – smaller than the 0.3 micron standard that defines a HEPA filter. 

Choosing an Air Purifier for Allergies: 
As we mentioned earlier, the most common allergens are things like dust mites, mold, pollen, and pet dander.  It may seem counter intuitive, but finding the best air purifier for allergies doesn’t really depend on what you are allergic to since these particulates are almost always greater than 0.3 microns in size.  While there are machines like the Austin Air Allergy Machine, which are specifically advertised as allergy air purifiers, any good, true HEPA air purifier will be sufficient to get rid of these allergens. 

The more severe your allergy symptoms, the higher-capacity machine you should buy.  For chronic allergy sufferers, we recommend at least 5 ACH for your bedroom air purifier.  For more information on allergies, see our How to Get Rid of Allergies page.

Choosing an Air Purifier for Asthma: 
This may be similar to choosing an air purifier for allergies if you know what your asthma triggers are.  If you are sensitive to the larger common particulates, most true HEPA air purifiers will do an excellent job of filtering them out.  However, asthma attacks can also be triggered by fumes and VOCs.  Ideally, an asthma air purifier should have both a HEPA filter and activated Carbon filter, depending on how sensitive you are to the environment. 

Similarly to allergy air purifiers and as a general rule, the more severe your asthma symptoms, the more powerful your air purifier should be in terms of CFM, which will translate to higher Air Changes per Hour (ACH) in the room or area.  For more information on asthma, see our What is Asthma? page.

Choosing an Air Purifier for Mold: 
Mold spores are typically 10 to 30 microns in size, so any standard true HEPA filter will be able to filter out just about 100% of mold spores that pass through.  If you need an air purifier for water damage restoration (high amounts of visible mold), select a HEPA model with a high CFM and a Pre-Filter.  Many brands produce multi-stage filtration systems that includes a Pre-Filter, such as Amaircare.
                                                                                                               

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Choosing an Air Purifier for Pet Dander: 
Pet dander is dead skin skills of animal origin; like pollen, it is something that widely aggravates allergic reactions or symptoms in people.  Most pet dander particles, including dog and cat dander, are between 5 and 10 microns in size.  A smaller portion, however, can be as small as just one micron.  Because of their structure and size, these particulates can stay airborne for hours. 

The good news is that any true HEPA filter will be able to filter out nearly 100% of the pet dander particles that pass through, since the rating standard is 99.97% of particles greater than 0.3 microns in size.  Though there are a few models out there that are advertised as specially designed for pets, such as the Austin Air Pet Machine, finding the right air purifier will be quite easy if your main concern is getting rid of pet dander. 

Since pet hair particles and skin flakes come in so many different sizes, one additional suggestion we make is to look for a machine that uses a Pre-Filter.  A Pre-Filter is designed to trap larger particles, thus keeping your HEPA filter unclogged and in the best condition to filter out the smallest of particulates.

Choosing an Air Purifier for Bacteria & Viruses: 
There are certain machines that are designed to kill harmful microorganisms, such as bacteria, viruses, and fungal spores. Many machines do a good job of filtering out these organisms, such as the hospital-grade Airgle AG900.  It is especially designed for ridding air of infectious organisms in addition to standard HEPA functions.  Another good option is an air sanitizer, with Airfree in the lead.  These types of air purifiers use heat or UV light to sterilize air that passes through the machine. 

Keep in mind that these machines will not literally sterilize an entire room; there will always be some particles that don’t go through the machine or come in from external sources.  In general, no air purifier or air sterilizer will completely eliminate all particulates, fumes, or microorganisms from the air.  The air that does enter the machine, however, can typically be filtered at rates between 99.5 and 99.99 percent.


Choosing an Air Purifier for VOCs: 
Volatility is essentially a measure of a substance’s tendency to vaporize into the air.  Rubbing alcohol, for example, is a lot more volatile than water; it evaporates from your hands far more quickly than water does.  However, there are dozens of volatile compounds outside, at work, and in your home as well.  These include Methylene chloride, Benzene, Toluene, chlorofluorocarbons, Perchloroethylene, and many other chemicals.  These fumes evaporate into the air off of things like paints, solvents, glues, nail polish remover, gasoline, machine exhaust, tobacco smoke, fireplaces, stovetop cooking, aerosols, dry cleaning, and more. 

These gaseous molecules are a lot smaller than the allergens we talked about earlier and cannot be captured by a HEPA air purifier.  They need to be captured by adsorbent materials, which are typically porous substances, such as Zeolites or activated Carbon.  You may have heard of people taking activated Charcoal pills to “detoxify” their body; the idea here is much the same. 

These are the best air purifiers for MCS – Multiple Chemical Sensitivity.  Volatile Organic Compounds are harmful for all of us, but certain people are more sensitive to them than others.  There is some debate as to whether or not MCS is an actual disease or just a manifestation of the variance with which people’s systems react to foreign substances.  In any case, an air purifier for VOCs will be easy to spot when looking at a list; air purifiers capable of filtering out VOCs will usually mention VOC in the title or a VOC filter in the description.

Choosing an Air Purifier for Smoke Odor: 
Like VOCs, smoke odor particles are smaller than those which a HEPA air purifier can capture.  In fact, they can be in the tenths, hundredths, or even thousandths of one micron.  As people who have tried know well, getting rid of smoke odor is one of the most difficult residential cleaning challenges.  You will need an air purifier with a VOC filter or an Ionizer, the latter of which may produce ozone, which is a significant drawback as noted earlier in this guide.   

The problem with smoke odor is that it adheres so well to surfaces like carpets, couches, and furniture, so you will need to combine HEPA vacuuming and scrubbing with an air purifier to remove the particles that get kicked up off of the surfaces.  Many websites will recommend an ozone generator for odors, but we do not since ozone is harmful to your lungs.  For more information and tips, see our article on Getting Rid of Smoke Odor.

Top Picks                                                                                      

Here are links to our website category sections, where we have compiled what we believe are the top four or five best air purifiers in each category.  We are constantly researching about new technology, listening to customer feedback, and reevaluating scientific trends so as to provide our customers with neutral and useful information. 

If you are looking for an all-around general purpose air purifier, check out the VOC section.  Because very few models are meant to work only on VOCs, most VOC models are a combination of HEPA technology and VOC filtration, with some featuring a UV light or additional filter as well.

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Best Air Purifiers for Dust & Mold
Best Air Purifiers for Allergies & Asthma
Best Air Purifiers for VOCs / MCS
Best Air Purifiers for Smoke
Best Air Purifiers for Pet Dander

By: Eugene Ravitsky

References:
http://www.epa.gov/iaq/pubs/airclean.html
http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=RAC
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