HEPA vs Electrostatic Air Purifiers

Here are some of the questions I get asked all the time:

First, do you use air purifier yourself, and do you believe them to be beneficial?

I use air purifiers in every room of my house and office and believe them to be truly beneficial. For instance, I have gone this whole past winter without a sinus infection or waking up stuffy, or with a sinus headache, which I believe is due to having an air purifier on 100% of the time in my bedroom at home.

What kinds of products should people avoid when shopping for an air purifier?

All I can do is warn consumers to stay away from any air purifier that does not include a HEPA filter. Anything that does not contain this kind of filtration, is not particularly efficient at best and at worst are beyond comment. My pet peeve is a multilevel marketing companies who are forbidden by the federal government to make any air cleaning claims for their ozone/negative ionizer. Which does not prevent them  thousands of well meaning multilevel marketing reps from making absurd claims for this “air purifier” which can be downright harmful. When the medical products testing department of the Canadian government tested this $699 “air purifier”, they tested the fan, the ionizer and the ozone separately, and guess what came out as the most effective part of the machine for removing smoke particles? The $30 fan, which drove the smoke particles to the walls.

Ozone does not remove dust or particles from the air. Ozone is used primarily in odor reduction after fires or smoke damage. Ozone is a documented as a health hazard by the American Lung Association and should only be used when human beings are aren’t close by.

Some air purifiers create ozone, which is meant to break down gases and odors. The EPA warns of ozone use as means of cleaning the air indoors due to the irritant and potentially harmful nature of ozone. Some air purifier manufacturers try to disguise the fact that their units produce ozone, by calling it activated oxygen. Activated Oxygen is Ozone!

Any particular air-purifier advice that comes to mind for the savvy (and allergic) consumer?

I think it is very hard for the average consumer to assess which is the best air purifier and most effective. In fact, it is downright confusing. When you read the average catalogue, all the entries for air purifiers sound like the best thing ever to hit this planet, they are not, but- all air purifiers have their strengths. This is why at Allergy Buyers Club we set out to review and rate all of our products, and actually tell people the minuses and pluses of every product that we sell.

I think consumers should be aware that air purifiers are not a magic bullet. They are not a substitute for cleaning your house thoroughly and removing settled dust with a good HEPA vacuum purifier.

The educated consumer should be aware of several factors in making their choice of air purifier. Here is my twelve item check list.

1. Type of filtration technology: Is it HEPA, HEPA-like, electrostatic, ionizers?
The types of technologies chosen by an air purifier manufacturer determine the filtration efficiency potential of the air cleaning device. In addition, how well these air cleaning technologies are implemented in the device, will determine the actual filtration efficiency of the device . Together with the air delivery, the filtration efficiency of the device establishes the effectiveness of the air purifier.

A. HEPA (High-Efficiency Particulate Arrestance) filters are only those specialized filters capable of removing 99.97% of particulates at 0.3 microns in diameter. HEPA filters, are made using principles adopted by the Institute for Environmental Standards, constructed of extended-media (pleated), wet laid filter medium (typically glass fiber paper), with separators, edge seal, sealant, and are housed in a rigid frame. True HEPA filters actually have to be certified.

Air filters based on 99.97% efficient HEPA are the industry standard in critical medical and hi-tech applications, because:
– trapped particles in the filter are never flushed out of the filter
– the efficiency of the 99.97% efficient HEPA media never decreases
– the HEPA filtration process is purely mechanical and produces no by-products like ozone.

It is important to not get confused that when air purifier manufacturers use the phrase “99.97% filtration at 0.3 microns”. This refers to the HEPA filter’s ability under ideal conditions and is not synonymous with the actual clean air produced by the device or the overall efficiency of the air cleaning unit. This is why we regard data from independent testing labs to be very important information.

“HEPA-type” filters 95% @ 0.3 microns are not true HEPA filter. They are used by air purifier manufacturers because it allows them to use weaker fan motors. Sometimes it is difficult to figure out whether true hepa filters are being used.

There is a new tendency by manufacturers to misuse the term HEPA for filter technologies that are not performing to the standards of the Institute for Environmental Standards, e.g. xxxxHEPA,or HEPAxxxx.

B. Electrostatically charged fibers (Electret air filter)
This filtration technology is used in air purifiers because it allows for a relatively high initial efficiency (typically between 50-90%) while allowing air to move easily through the filter. The disadvantage is that this filter technology gets less efficient with use, as the fibers lose their electrostatic charge as they are get loaded up. This can loose efficiency and cause the filter to drop to less than 20%.

C. Electrostatic precipitator
This filtration technology uses ionization to charge dust particles and then metal plates or filter media, which carry an opposite charge to collect them. The starting efficiency of these systems tends to lie in the 50-80% range. When the collection surface gets dirty this efficiency drops significantly. On top of them losing effectiveness, electrostatic precipitators can also generate ozone.

D. Ionizer
Ionization by itself uses high voltage to negatively charge airborne particles. Since pure ionizers capture no particles, charged particles are simply released into the room where they tend to attach to surfaces. This means that ionizers may only have a temporary effect of eliminating particles from the air. The EPA also draws attention to the fact that these charged particles when inhaled may have a higher propensity to get trapped in our lungs and become harmful to our lungs.

2. Size of filter in the machine: When you think about for a moment, a HEPA filter with a larger surface area, will catch more particles than a smaller one. Just because an air purifier has a HEPA filter, does not mean they are all created equal.

3. Filtration efficiency: Here is a little known statistic about air purifiers. They vary in their efficiency. Some air purifiers are designed so that there is plenty of places for particulates to go other than into the hepa filter. In the end, these particles are exhausted out of the machine into the air of the room where they are inhaled by the room inhabitants.

4. CFM level, or cubic feet per minute level: A good air purifier will give you at least 6 air changes per hour. Remember you will not want to run it on high speed except when you are out of the room as it will be too noisy. So you need an air filter which will give you the required air changes at low fan speed. The CFM rating is a good indicator of the probable air changes. We do not give high marks to any air purifier below a 400 CFM rating. Also remember when you look at the specifications of all air purifiers, the square footage covered, is rated for high fan speed. Therefore on low fan speed, that air purifier you think will cover your whole apartment will only actually cover effectively your bedroom. When you locate your air purifier in your home, remember that a room air purifier is most effective located in a single room, it will not be so effective if you expect it to clean multiple rooms simultaneously.

5. Filter replacements Costs: If you have separate filters for the pre filter, HEPA filter, and carbon filter, these are often the least expensive to run in the long run. The pre-filter will absorb the largest particulates and save the life of the HEPA filter which is often the most expensive element in the machine. Air purifiers vary wildly as to the life and cost of their filters which you should check into carefully before you make a purchase.

6. Ease of changing filters: In your enthusiasm in buying an air purifier do not forget to pay attention to how easy or difficult it is to change filters. Some machines are so complicated that you are tempted to give up on them entirely [we even sent one back to the factory to change filters we got so confused].

7. Separate filters: The better air purifiers will have a prefilter, hepa filter and carbon filter [for odors and gases]. Having a prefilter will extend the life of your hepa filter. If the three filters are combined, which is cheaper to manufacture, you will need to replace the filters more often. This means that the filters are not changed at the optimal interval. For instance , a gas filter will normally need replacing months, if not years, before a hepa filter needs replacing.

8. Filter Change Indicator Lights: You do not want to pay for expensive filter changes sooner than you need them, yet you do not want to be running an air purifier with a clogged filter. Therefore, we believe that the best air purifiers come with “change filter indicator lights”. There are different technologies used for the “change filter” light, the crudest being a count on the number of hours the air purifier has been running. An improvement on that is hours x fan speed. No machine is currently measuring the amount of pollutants absorbed by the filter. Naturally your filters will last longer in a nice clean suburb as opposed to one located in the center of New York City.

9. Is there separate filter (sometimes called media) used for odor and gas removal? How much of it is there and what type of carbon is used? Indoor air contains in addition to dust particles, it often gaseous pollutants and odors. Pollution is usually a gas rather than a solid allergen, so different filter technologies are needed to filter gases. Clearly, more is better than less but here quality makes a significant difference to the adsorption rate. Carbon is often mixed in with zeolite, a cheaper fill. Carbon comes in three kinds- dust, coconut shell or granulated. The latter is the most expensive.

A. Granular activated carbon
This substance is used in many larger air purifiers. While it may be effective for the removal of gases and odors that are drawn through the unit, it often significantly reduces the airflow of the air purifier, which means that not enough air is being cleaned by the unit.

B. Granular activated carbon and zeolite and/or potassium permanganate
Zeolite is a mineral. Since it is less expensive than activated carbon, many manufacturers like to mix it in with activated carbon to lower their production costs. Some manufacturers claim that zeolite is efficient for the control ammonia. This assertion lacks scientific foundation. Potassium permanganate has the capacity to remove specific gases such as formaldehyde. It is however in many air purifiers the source of strong dusting, which makes it unacceptable in many dust sensitive environments.

C. Carbon impregnated pad
This technology relies on a fiber pad to be impregnated with carbon dust. Due to glue used in binding the carbon dust to the fibers and the small amounts of activated carbon used, the effectiveness of this type of activated carbon filters is very limited. Many times, carbon-impregnated pads are also used to function as pre-filters.

10. Noise level: Most HEPA-based air purifiers on high fan speed sound like a train going through the room. There is also a great deal of variability in terms of noise. We have also found that many manufacturers are dreaming when they describe their air purifier as “whisper quiet” or “ultra quiet.” Most air purifiers are so noisy that my husband refuses to have them going in our bedroom at night. Luckily, we now have one which he can hardly hear and passes the noise test. One way around this problem is to put the machine on high speed when you are out of the room and turn it down to low fan speed when you occupy the room. The best machines have automatic timers which allow you to program the air purifier to go on high when you are not occupying the room.

11. Reliability and Warranty: A good air purifier will last for years and the main motor will usually have a five-year life.

12. Will the manufacturer accept returns? Most good manufacturers will allow a 30 day return for an air purifier if it does not suit your needs or you find it ineffective. You would be responsible however for shipping charges if the machine is not defective as such.

My Conclusions?

I still think it is hard for the average consumer to make sense out of all this. We deluge people with information on our site and still people call us up asking which one would we pick for their situation.

My personal best picks are the following:

A. Blueair – for quiet in the bedroom, sacrificing a bit in efficiency but allowing you to sleep with the machine on fairly high fan speed

B. IQair for most of the house and putting it on high when the room is not occupied as it is fairly noisy on high fan speed. I think it is the best engineered air purifier on our site.

C. QuietPure offer great coverage and excellent filtration of allergen and gases. We consider them very quiet on the low and medium speeds.

D. For an economy buy, the Austin Healthmate is a work horse and is nothing fancy but good value.