HEPA Air Purifiers 101

What are HEPA air purifiers ?

HEPA air purifiers are air purifiers which clean the air through the use of HEPA or High Efficiency Particulate Air filters. HEPA filters are high efficiency filters capable of filtering particles up to 0.3 micron in size at 99.97% efficiency. They also can filter particles smaller than 0.3 micron, but at reduced efficiency.

Why Choose an Air Purifier with HEPA filter ?

Air purifier with HEPA filter should be your top choice if you want to have a significant improvement of your indoor air quality. A True HEPA filter is effective in trapping big and small particles with 99.97% efficiency up to 0.3 micron in size.

But, is air purifier with HEPA filter worth it, considering the high cost of HEPA filter replacement, especially those that came from the top air purifiers ?

In order to answer this question, we need to look at the size of air particulates. The air that we breathe consists a lot of particulates, sized from 0.0001 micron to 10,000 micron. An ordinary filter or a non-True HEPA filter (often called: HEPA-like or HEPA-grade filter) are usually very effective in curbing out particles up to 5 micron or so.

But guess what ?

The lung-penetrating particulates are somewhere between 0.3-5 micron. Particulates these sizes stay suspended in the air and are lung-penetrating because they are not big enough to be stopped by our nose, and are not small enough to be exhaled easily by our lung. This is the size of particulates most efficiently trapped by a HEPA filter. Hence, an air purifier with HEPA filter is a good choice if you want to minimize the presence of lung-penetrating particulates in your surrounding.

How Do HEPA Air Purifiers Work ?

Basically, HEPA air purifiers clean the air by passing the dirty air through the HEPA filter and exhalling the clean air out to the room. Some HEPA air purifiers are equipped with a prefilter so that the big particulates in the dirty air hit the cheaper filter first and leave the HEPA filter to deal with finer particulates. That way, the expensive HEPA filter does not have to be replaced so frequently.

Although HEPA filters already filter out particulates at 0.3 micron or bigger, the majority of particulates (90%) including gases are smaller than that. Sure the smaller particulates (smaller than 0.3 micron)are easier to exhale from the lung, but for people with health problems or with overwhelming number of such fine particulates in the surrounding (for instance: smoke, chemical outgas, pet odor), it helps to have a HEPA air purifier which is equipped with a gas absorbant, such as a chemical or carbon filter. Hence air purifier manufacturers often also include a carbon filter, consisting of activated carbon, to help trap such fine particles. Of course the ability of an air purifier to control odor and smoke also depends on the amount of activated carbon embedded in the unit. Some cheaper air purifiers usually have stripes of carbon, whereas premium air purifiers pride themselves for putting in 5 lb of carbon or more in the unit.

Finally, it is also known that HEPA air purifier's manufacturers sometimes include UV or other germicidal agent such as silver screen in their units to help kill germs. Actually, an UV or germicidal agent is not a priority if the other filters do the good job in filtering small particulates. In this kind of unit, germs will automatically be filtered. In fact, most premium air purifier lines do not have a UV light or other germicidal agent. And yet, they are very effective in curbing dead particulates and live germs alike. The concern of having a UV light is that it can make the unit to produce ozone, a potential lung irritant, as a by product.

In short, the stage of cleaning air using a HEPA air purifier is as follows:

• Dirty air from surrounding is sucked up to the air purifier unit and is passed to a series of filter by the use of fan.
• Stage I (optional): The dirty air is passed through a prefilter. Not all HEPA air purifier units has a prefilter, but most have it to reduce the frequency of HEPA filter replacement.
• Stage II (optional): Some HEPA air purifiers use carbon filter to filter out gases. So once the air is passed from prefilter, it gets to the carbon filter.
• Stage III: Air is then passed through the HEPA filter.
• Stage IV (optional): Air is exposed to the UV light to help kill microorganism.

Do HEPA Air Purifiers Work ?

If you ask whether a HEPA air purifier works, then the answer is yes. If the HEPA filter is a true HEPA and the unit has a tight housing, then it works. What we mean by 'work' is that it will do what it is supposed to do. However, there is no guarantee whether this will get rid of your health problems, because most health problem is multifactorial. Hence sometimes it is difficult to pinpoint whether a particular person's asthma or allergy, for instance, will improve significantly with the use of an air purifier. Having said that, there has been a lot of people whose health condition improved by the use of an air purifier.

(For more discussion on this, look at our article on whether air purifiers really work)

We mention above that in order to work properly, a HEPA air purifier should heave a true HEPA filter and tight housing. Let us explain one by one.

In order to have a filtration efficiency of a HEPA filter, a HEPA filter air purifier should have a true HEPA filter. Note the word 'true' here. It means that the HEPA filter embedded in the unit is a real one, not the HEPA-like filter or HEPA-grade filter. Therefore, if you're looking for an air purifier with HEPA filter, don't settle for one which has a HEPA-like or HEPA-grade filter since they have lower quality. Go for the ones which have a True HEPA filter.

It is also important for an air purifier to have a tight housing, so that the machine does not allow the dirty air to bypass the filter. IF the housing is not tight, there will be a leakage of dirty air, which means that the air purifier will exhale some dirty air. The tighest housing can be found with premium air purifier. But if you're looking for a cheaper alternative, you can get the second tier one. Their quality is not as good as the premium one, but they're still pretty tight and they have True HEPA filters. Some even include some carbon for odor control.

(To see air purifier tier system and what air purifier gets what tier, go to our air purifier review page.)

Are HEPA Air Purifiers Safe ?

In contrast to some electronic air purifiers such as ionic air purifier and ozone air purifier, HEPA filter air purifiers are the safest air purifiers you can get. Since it works by mechanical means, there is no ozone, a potential lung and respiratory pathway-irritant, emitted. If you choose the ones with metal casing and non-toxic paint, there will be no outgassing either.

Advantage of Choosing Air Purifier With HEPA filter

• Safe.
• It works and has a high efficiency in curbing out lung-penetrating air particles.
• If you get a premium quality HEPA filter air purifier, there is a big chance that it will help your health problem.

Possible Drawbacks in Owning an Air Purifier with HEPA filter

• Maintenance cost can be expensive because of the need to replace the HEPA filter periodically.
• Possible hassle of installing the HEPA filter. You may need tool for changing the HEPA filter, but there are some air purifiers which are very easy to change. If you are DIY-challenged, make sure you get the one which has an easy-to-replace HEPA filter.
• Noisy. A HEPA filter air purifier needs fan to draw air into the unit and to the filter. The higher the speed, the noisier it gets.

Related Articles

Summary of different home air purifier system or technology used to purify air.

Other technologies to purify the air:

• Carbon Air Purifier
• Ozone Air Purifier
• Electrostatic Air Purifier
• UV Air Purifiers
• Ionic Air Purifier

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