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How to Buy the Best Air Purifier for Your Home, Office, & Whole-House
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Buying an air purifier is an important decision (no matter what your budget) and with the hundreds of air cleaning products available it’s a challenge to figure out what to buy and who to trust. The following report is designed to give an overview of important information to consider when choosing a home air purifier, office air purifier, and/or whole-house air purifier that’s right for you.
Please note that we use the terms air purifier, air filter, and air cleaner interchangeably and consider all these terms to be equivalent for the purposes of this article.
What is Air Pollution?
Air pollution is made up of particles and gases. Without getting too technical – particles are something solid or liquid, light enough to float in the air while gases are gas molecules not “normally” found in the air. Note that chemicals are not always gases -- there are specific chemicals that are mainly absorbed by particles.
Particles:
The majority of home air purifiers clean “particles” from the air so it’s important to understand that particles come in a whole range of sizes. E.g.:
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Viruses: 0.01 – 0.05 micron
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Bacteria 0.3 – 3 micron
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Smoke: 0.01 – 5 micron
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Cat allergens: 0.05 – 3 micron
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Mold spores: 3 – 30 micron
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Pollen: 10 - 100 micron
These sizes may appear to be similar (i.e. small) but in fact it’s like comparing the size of a jumbo jet to a golf ball. Ultra-fine particles smaller than 0.1 microns make up over 80% of all airborne particles and because of their size can stay in the air indefinitely, enter deep into the lungs, and are small enough to be absorbed into the blood stream and cells. Note that most air cleaners filter coarse particles but are much less efficient when filtering fine and ultra-fine particles. When comparing air purifiers, be sure to take the size of particles into account.
Gases:
Most gaseous chemicals can be removed from the air with appropriate gas filtration technology. However, it’s important to realize that to be effective a filter needs to be “matched” to the gaseous chemical or chemicals to be filtered.
What Do You Need?
Take a moment to clarify what you want your air cleaning solution to “do” or what the problem “is” you’re trying to solve (or for what specific purpose)? This will help prioritize those air cleaning features that are important to your specific situation. Here are some examples:
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My family and I are healthy but we live in an urban area and want to improve the general air quality in our home.
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The apartment I rent has just been remodeled and smells of fresh paint and carpet. I want to remove the odor and the toxic chemicals from the air.
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I have allergies and want to turn my bedroom into a safe house so that I can sleep better at night.
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I spend a lot of time at work and with all the photocopiers, printers, and carpet cleaning that goes on I’m concerned about the air quality in my personal office and want to improve it.
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I have a newborn baby and want to ensure that the air in her bedroom is as pure as possible.
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I want to remove pet odors from my home.
What Size Area?
Next, decide on what size area you want your air cleaning solution to handle. Is it the whole house or a specific room (or rooms)? For the home, your major options are:
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Room Air Purifiers (Stand-Alone Air Filters)
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Whole-House Air Purifiers (In-Duct Air Filters)
For the office, typically the only option available is room air purification. If you’re the boss, a commercial air filtration system is of course an option (but is not covered in this article).
Room vs. Whole-House Air Purification
Note that whole-house air cleaning systems are not necessarily “bigger” versions of room air purifiers. Both solutions can serve different purposes and offer specific benefits. Keep the following points in mind as you read on:
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Whole-house air purifiers typically work in conjunction with the existing heating, ventilation, and/or air conditioning system (HVAC). Air is only filtered when the HVAC system fan is running.
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Room air purifiers handle gaseous pollution and odors (if designed for this type of use) while whole-house air purifiers do not (due to the amount of air flow required to clean the air in an entire home).
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Whole-house purifiers typically operate at a lower efficiency (due to the large area that needs to be covered).
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It’s possible to achieve whole-house air cleaning by using multiple room air purifiers.
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Room |
Whole-House |
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Advantages:
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Easy to setup (no installation necessary)
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Portable (can be moved to any room)
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Filter changes and cleaning typically doesn’t require an expert
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Can be running even when the HVAC system is not.
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Does not reduce the effectiveness of the HVAC
Disadvantages:
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Advantages:
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Cleans the air in an entire home
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Does not take up additional space in the home
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Does not generate additional noise
Disadvantages:
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Furnace Filters
If your house has a heating, ventilation, and/or air conditioning system (HVAC) it will have a furnace filter. For the purposes of this article we don’t consider furnace filters to be a quality air purification solution due to their limited filtering capabilities. However, the American Lung Association has a number of good tips on furnace filters
here.
Room Air Purification (Stand-Alone Air Filters)
Room air purifiers come in all sorts of sizes and shapes and also use a wide range of air cleaning technologies (or combinations of). The following is a list of points to be aware of when selecting a quality room air purifier:
The Hype:
Manufacturers are constantly competing for the attention of consumers and their marketing departments often hype amazing “new” technologies. The reality is that there are a core set of air filtering technologies available to all air purifier manufacturers. (Truly unique and new technologies are of course being developed but will typically be utilized by industry and hospitals where air cleaning is critically important before being used in home purifiers.) Keep in mind that it’s how these technologies are implemented and for what specific purpose they are designed that is important.
The Numbers & Air Purification Claims:
It’s incredibly confusing sorting through all the claims, numbers, and certifications for each air purifier on the market. Even more difficult is trying to accurately compare one product with another because there is no one recognized standard to compare them by. Manufacturers often make similar claims to each other so be sure to read the fine print and try to get to the bottom line -- “total system efficiency”. For example, it’s of little value to rate individual components that make up the air purifier -- what’s important is the overall efficiency of the air purifier since there are many factors that ultimately determine final air quality. Air purifier efficiency measurements may also be taken from a “sweet spot” (e.g. the very center of a filter) whereas the air passing through the sides of the filter may receive far less cleaning.
Maintenance and Filter Replacements:
All air purifiers require regular maintenance, however they vary widely in the type of maintenance required and the effort involved. Maintenance is critical and ultimately determines the long-term effectiveness of the air purifier. The trick is to determine what kind of maintenance you're prepared to do. For example, are you more likely to purchase filters on a regular basis or would you prefer to spend time cleaning collector plates and screens? Look for air purifiers that require minimal maintenance (and preferably no tools) and that display an indicator when maintenance is required.
Noise:
Almost all air purifiers create noise but because most manufacturers use there own noise measuring standards it’s difficult to make comparisons. Note that some air cleaners that make little or no noise may also be ineffective. Other air purifiers can create noise that sounds “unpleasant”. Also, look for air purifiers that have speed settings so that they can be turned down during the night and up during the day (when noise is not as much of an issue).
Long Term Efficiency:Look for air purifiers that have long term efficiency. Many air purifiers have a high efficiency when they’re new but start to degrade over time. In fact, in as little as 6 months air purifiers can drop in efficiency by 20-30% and more if they're not maintained/cleaned regularly. Check out “True HEPA” that actually becomes more efficient with use. Programmable Timer: While perhaps obvious, it’s worth noting that if an air purifier is not being used then it’s not doing any good (no matter how much you spend on it). A programmable timer that automatically turns the air purifier on or off based on your schedule will ensure your home’s air is being cleaned without you even having to think about it.
Air Leakage:
A well designed air purifier will have little or no “leakage” where air literally leaks around the filter technology. If components and filters are loose or have gaps then it doesn’t matter how good the filter technology is because polluted air simply bypasses the filtering process and is re-circulated back into the home. Look for air purifiers that have an airtight housing design.
AHAM “CADR”:
The “Clean Air Delivery Rate” is a common certification found on home air purifiers. Note that CADR tests the performance of an air purifier for the first few minutes of operation only, does not test performance for ultra-small particles, and does not test effectiveness for gaseous pollutants and odors. There is also no test standard for whole-house air cleaners.
Exterior Casing:
Air purifiers typically come in plastic or metal casings. Avoid soft plastics since these can off gas and can add to indoor pollution. Hard plastics typically have very little or no off-gassing and will not scratch or dent. Look for casings that are internally molded to fit the internal workings or the purifier (thereby limiting the amount of soft plastic and rubber required internally to seal and stabilize internal components). Metal casings do not off-gas but they typically require the addition of internal soft plastics and/or rubber to seal and stabilize internal components than hard plastics.
Air Delivery:
Air delivery is the amount of air that an air cleaner is able to clean and is usually stated in cubic feet per minute (cfm). Be sure that the air delivery stated is that of the overall system and not the unit without filters or the fans capacity alone.
Ozone:
The topic of ozone is controversial. Some claim that low levels of ozone is safe to breathe, while the American Lung Association says that ozone is a potent lung irritant with damaging health effects and does not suggest ozone generators be used, and the EPA says that relatively low amounts of ozone can cause chest pain, coughing, shortness of breath, and throat irritation. For an air purifier that will be used inside the home while people are present, it seems prudent to avoid any product that generates any level of ozone.
Carbon Monoxide:
There are currently no home air purifiers that filter carbon monoxide. Sources of carbon monoxide in the home include: unvented kerosene and gas space heaters; leaking chimneys and furnaces; back-drafting from furnaces, gas water heaters, wood stoves, and fireplaces; gas stoves; generators and other gasoline powered equipment; automobile exhaust from attached garages; and tobacco smoke. General information including common carbon monoxide sources and ways to reduce exposure are available in the EPA’s General Information article.
Whole-House Air Purification
Much of what applies to stand-alone air purifiers also applies to whole-house air purification too. However, the following is a list of additional points to be aware of:
Installation:
A whole-house air cleaning system is only as good as the actual installation that is done in your home. Even the best system won’t perform if it is incorrectly installed. Ensure your tradesman is licensed to install your air purifier’s brand and model and ask for an air quality guarantee.
Air Quality Guarantee:
Because whole-house air purification is a substantial investment it’s important to get a guarantee that your installation is working correctly as per the manufacturer's specifications. Ideally, get a measurement of air quality before and after installation and make the comparison yourself because air pollution is typically invisible to the naked eye.
Maintenance:
Just like stand-alone air purifiers, whole-house air purification systems require maintenance too. However, maintenance typically needs to be performed by a specialist so there’s an additional servicing cost involved. Look for whole-house air purifiers that require minimal maintenance (e.g. once every 2-3 years) and be sure to get an idea of the total maintenance cost involved when making comparisons between air purification systems.
Pressure Drop:
Because the whole-house air purification system needs to work in conjunction with the existing heating, ventilation, and/or air conditioning system in the home it’s important to consider the level of “pressure drop” that will be created. Pressure drop is the additional pressure created when air is pulled through a filter. A high pressure drop can lead to a myriad of problems including frozen coils, premature fan motor burnouts, return leaks, and high energy costs (since the entire system needs to work harder).
Minimum Efficiency Reporting Value (MERV):
While MERV is considered the gold standard for efficiency rating and is useful for comparing whole-house air purifiers, look for manufacturers who have a rating from an independent laboratory. Also note that the MERV rating is meaningless without the corresponding “airflow” at which the test was conducted (and that a lower airflow = higher MERV rating). It’s also worth noting that the MERV rating is no indication as to whether an air cleaning system is effective for ultra-fine particles of smaller than 0.1 microns.
Bringing In Outside Air:
Because whole-house air purifiers are not able to effectively clean air containing gaseous chemicals and odors, consider having outside air brought in automatically through the whole-house air cleaning system (if possible). This will help flush these pollutants out of the home and will also draw in additional oxygen.
Air Cleaning Technology – The Bottom Line
There are many different home air cleaning technologies available but only a few of these technologies are used in critical commercial applications. Critical applications must have air cleaning solutions that are high-performance, have a high reliability, and produce no undesirable by-products (e.g. ozone, charged particles, and harmful chemicals). Seek out the following technologies (that meet this criteria) for your own home:
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Mechanical filters particlary HEPA and HEPA type filters (used in hospitals, cleanrooms, and laboratories).
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Activated carbon (used in cleanrooms, chemical plants, and control rooms).
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Chemisorption (used in airports, chemical plants, and hospitals).
The following sections give an overview of common technologies being used in home air purifiers (particle and gaseous) and points worth noting.
Air Cleaning Technologies for Particles
Ionization:
A needle, carbon brush, or wire with high-voltage charges airborne particles negatively and these charged particles are attracted to surfaces (room surfaces or a surface inside the air cleaner). Particles may be attracted to walls, floors, tabletops, draperies etc. and may be dispersed back into the air at a later time. The EPA says that charged particles can also be deposited in the respiratory tract and that the use of ion generators may not reduce the dose of particles to the lung.
Electrostatic Precipitation (Electronic or Ionic Air Cleaning):
In the first stage (ionization section) a wire, needles, or carbon brushes with high-voltage give(s) the particles in the air stream a positive charge. In the second stage (collection section) plates, cells or, filter media, attract the positively charged particles. The advantage of this type of technology is the high airflow and that the collection plates can be cleaned (i.e. no replacement filters required). However “blowback” is possible if the collection plates lose power (e.g. unit is switched on/off) since it’s the charge that keeps the dirt “on” the plate. Ozone is also generated (see above).
Ultraviolet Radiation:
An ultraviolet tube generates visible and invisible radiation for the purpose of killing microorganisms. The benefits of UV light are convincing but it's difficult to determine actual kill rates of microorganisms since it depends on both the intensity (UV lights get weaker over time) and the contact time in which microorganisms are exposed to the UV. The Centers for Disease Control (CDC) states that UV light in hospitals does not add to the effectiveness of HEPA filtration.
Air Washing:
Water is mixed with air in order to wash air pollutants from the air. While this method requires no filters it only works with very coarse dust and water soluble gases. The presence of water allows fungi and bacteria to grow and requires regular cleaning.
Incineration:
Convection moves air through a heating coil (same principle as a hair dryer) and incinerates particles. While this method requires no filters or fans it generally moves too little air to make a difference in a normal environment.
Charged Media Filtration:
A meshwork of synthetic electrostatically charged fibers that attract particles. The advantage of this technology is that the less dense media allows for more airflow and that the filter efficiency is high due to the magnetic effect of fibers. The disadvantage is that filtration generally gets less efficient with use. It's worth noting that many of these types of filters call themselves HEPA.
Mechanical Filtration:
Mechanical filters are filters that hold particles back based on mechanical principles (i.e. straining, impingement, interception, diffusion). Mechanical filters come in different types and efficiency categories but have one thing in common and that is their efficiency increases with use.
HEPA Filtration:
HEPA stands for high efficiency particulate air and it is a pleated filter that works on mechanical filtration principles. There are different grades of HEPA available but “true HEPA” efficiency is more than 99.97% and 0.3 microns is made of wet laid micro-glass fibers. Hyper HEPA will filter down to 0.3 microns at 99.97% and .003 microns at 99.5%. HEPA has a high initial efficiency, efficiency increases with usage (airflow decreases), and there is no re-release of particles. It's worth noting that a manufacturer can call almost any type of mechanical filter HEPA so be sure to check the efficiency rating to determine if it’s “true HEPA” or better. Industry and hospitals use HEPA due to its reliability and low maintenance. HEPA filters must be replaced and cannot be cleaned.
Air Cleaning Technologies for Gases
Ozonation:
High voltage causes the oxygen molecules in the air to combine to ozone. As mentioned above the subject of ozone is controversial and both the American Lung Association and EPA advise against its use.
Photocatalysis:
UV light shines onto a catalytic surface and converts gases into carbon dioxide and water (and can produce ozone as a byproduct). The EPA recommends activated carbon for greater effectiveness.
Adsorption:
Physical process of binding gas molecules to a large surface. Note that temperature changes can reverse this process (desorption) and trapped pollutants can be re-released into the air.
Chemisorption:
In the first stage, gas molecules are physically attracted onto a carrier media and in the second stage the trapped gas molecules are chemically broken down. Since there is a chemical process involved, there is no reemission of gaseous pollutants.
On a Final Note
Nothing is more important to overall wellness than air quality but it’s worth noting that an air purifier is only part of the solution. Be sure to allow plenty of fresh air to circulate around your home to increase the amount of oxygen in the air and to flush out pollutants. Use safe and natural cleaning products whenever possible. Choose chemical-free and natural materials wherever possible especially for major household contents such as carpet (or flooring), paint, furniture, and drapes.
Jun-2008
