Filtration Efficiency: HEPA, Micron, etc.

In recent years our awareness of how the quality of the air we breathe affects our general health has been heightened. One aspect of air quality which is largely affected by the filtration efficiency of a vacuum cleaner is that of airborne dust and allergens. A vacuum cleaner uses the force exerted by its air flow, along with brushing action, to pick up the dirt and dust and carry it into its dustbag or other dirt container. Except for Central Vacuum Systems with external exhausts, this same air flow is recirculated back into the living environment after passing through the vacuum cleaner.

Trapping Allergens Produced by Dust Mites

One of the most common dust related allergens is produced by the dust mite. While the dust mite itself is so small that it is just barely visible to the naked eye under the right lighting, it is still relatively large (about 125 µm long) compared to the particles containing allergens that are produced by it. It is the protein DER p1 found in the mite's droppings that is the actual allergen which affects those who are sensitive to them. The size of these particles are quite small, initially measuring about 10 to 24 microns (micrometer). To give you an idea how small that is, the diameter of the human hair is about 80 to 100 µm in size. It is estimated that there are roughly 10,000 dust mites in the average bed, each excreting about 20 pellets per day. These pellets can break down into even smaller particles when disturbed. Just think what the populations are deep within your carpets! They are scavengers that feed on human skin scales but do not bite humans. To learn more about these minute creatures, see our article titled "The Mighty Dust Mite."

In order to prevent these minute particles containing allergens from being recirculated into the air you breathe, a vacuum cleaner's filtration system must be very efficient at trapping particles that small. The current cutting edge in vacuum cleaner technology is in the area of improving the filtration efficiencies of vacuum cleaners. The vacuum cleaner industry is taking advantage of the development of advanced filtration media to provide much higher quality exhausted air than was possible just a few years ago. Where there are special dust related sensitivities, vacuum cleaners which have extremely high filtration efficiencies that meet the HEPA specification are often very helpful. To reduce the effects on allergies and asthma caused by the allergens in dust mite droppings, look for a completely sealed vacuum cleaner with a HEPA filter.

HEPA and ULPA Filtration Specifications

HEPA (High Efficiency Particulate Air) is a filtering efficiency specification for filters developed by the Atomic Energy Commission during World War II to effectively remove radioactive dust from plant exhausts without redistribution. A HEPA filter must retain all particles as small as 0.3 µm in size with an efficiency rating of 99.97%. The phrases "as small as" or "at" mean that if all particles were that small, it would still have that efficiency. This should not be confused with the phrase "down to" which may mean a mixture of particle sizes for the stated efficiency.

The HEPA acronym is used primarilly in the USA whereas Europeans often refer to the same filter as an S-Class filter. This indicates that the filter meets standards like the British Standard 5415 and German norm: DIN 2418B Ti-E EU 13 for filtration performance.

ULPA (Ultra Low Penetration Air) is a filtering efficiency specification for filters used in environments like pharmaceutical labs wherein the highest degree of clean air must be maintained. An ULPA filter must retain all particles to 0.12 µm in size at an efficiency rating of 99.999%. The Nilfisk GM 80 Portable Dust Collector is an example of a commercial vacuum cleaner which can be equipped with a Certified ULPA filter. Due to its air tight seals, it actually meets the ULPA specification for net filtration.

Certified HEPA and ULPA filters are tested and marked with a certification number which gives the user the assurance that the stated specification is actually being achived by the filter. It is very important to have a completely sealed system so all air flow must pass through the HEPA or ULPA filter to be cleaned by it. The HEPA filters that Miele, Lindhaus and Nilfisk use in their vaccum cleaners are tested and certified that they meet the stringent HEPA specification.

Another approach to HEPA filtration is to have a series of bags and filters in a completely sealed system which are so efficient that the stringent HEPA specification is achieved for the complete vacuum cleaner system. This often can reduce the operating expense since more expensive HEPA filters don't need to be replaced. SEBO S-Class vacuum cleaners use this approach.

Some cleaners have HEPA Type filtration which is better than standard filtration but may not meet the stringent HEPA specification. Other vacuum cleaners have actual HEPA filters in systems which are not well sealed. These have significant dust leakage through seams in their cases, greatly reducing the beneficial effects of their HEPA filters. If dust related allergies or asthma are an issue, we recommend only cleaners with Certified HEPA filters in completely sealed systems.

Micron and Electrostatic Filters

Some vacuum cleaners use special filter media capable of high filtration efficiencies which are close to, but do not meet, the HEPA specification. Filtrete by 3M used by companies like Lindhaus is one such product as well as the "Super Air Clean" filter by Miele. Both of these filters have an efficiency of about 98% at 0.3 µm so they are still quite effective. These two companies have vacuum cleaners which enable their owners to use either these less expensive filters which are packed with their bags or their optional Certified HEPA filters. These filters are constructed to trap fine dust and by causing an electrostatic charge to be created as air passes through them. This charge causes the fine dust to cling to their fibers. Filters of this type are sometimes called micron filters or electrostatic filters.

Ongoing Cost of Using HEPA Filters

As mentioned above, HEPA filters are very effective but this stringent filtration comes with a price. These filters are much more expensive than other types of filters and need to be changed fairly frequently - every year or two. The cost of replacing Certified HEPA filters is about $1.00 per week if changed yearly. This can add up in the long run but the positive effects are well worth the added cost for those who suffer from dust related allergies and asthma.

For those who don't have these sensitivities but still want outstanding filtration, use of micron or electrostatic filters is a better, more cost effective option. I appreciate the way Miele and Lindhaus vacuum cleaners provide the option of using either type of filter. If slightly less than HEPA filtration is currently adequate, a cost savings can be realized but if someone in your household develops allergies or asthma, the more effective Certified HEPA filters can be used without the need to purchase a new vacuum cleaner.

An important aspect in reducing the cost of replacing HEPA filters is to have a series of effective filters preceding them. This prevents most of the fine dust and dirt from reaching and clogging these filters. This also improves air flow since larger particles don't block the small pores in the filter media.

So it Traps 100% of Dust Mites!

I've seen vacuum cleaner manufacturers bragging about how their cleaners trap 100% of Dust Mites, Pollens, etc. Some even have this printed right on their filter holders. So what! As mentioned above, dust mites are quite large compared to their minute droppings. Pollens are quite large as well. A cleaner with this degree of filtration may help those who suffer from Ragweed and other pollens but not those who suffer from the primary allergen found in house dust, the protein Der. p.1 in dust mite droppings. Since some companies make vacuum cleaners with outstanding filtration, others try to appear just as good or superior by using these misleading phrases. Sorry, but phrases like "capable of filtering out over 99% of pollens, 98% of selected bacteria and 95% of all yeast and fungi" and "filters a wide range of airborne particles including many pollens, spores, other allergens and dust mites" don't really cut it for many allergy and asthma suffers.

Some other forms of misleading phrases revolve around how filtration is represented. Some companies will simply state a filtration efficiency percent without stating the size of the particle being measured. A variation of this is to state a percentage with the phrase "down to" when stating the size. Some even state "down to" a specific size without stating the efficiency percentage. The statement "electrostatically charged fibers retain dust and pollen down to 0.1 micron (micrometer) in size." is a classic example of how very misleading these statements can get. This actual phrase refers to a dustbag which probably has an efficiency of only 75% at 0.3 micrometer!


High filtration efficiencies are very important to all of us, especially those who suffer from dust related sensitivities. Improving the quality of the air we breathe can be important to our general health. Vacuum cleaners pull the air through the carpet fibers, taking with it the dirt including dust mite droppings which contain a common allergen. To effectively remove as many of these microscopic particles from the air flow requires a very efficient filter and a well sealed vacuum cleaner system. Most high efficiency HEPA and ULPA filters are placed at the exhaust of the cleaner so they also retain carbon which wears off of the motor brushes. Any leaks through the seams in the case can have a dramatic negative effect on the actual filtration efficiency.

For those who do not suffer from dust related sensitivities, well sealed vacuum cleaners with micron, electrostatic or "HEPA Type" filtration will do quite well. Having the option to use either a certified HEPA filter or micron filter is a nice feature which is available on some more deluxe vacuum cleaners like Miele and Lindhaus.

To learn more about filtration efficiencies and factors which effect the net filtration of vacuum cleaners, read the article about the Dustbag Performance and Filtration Efficiency. For additional help with allergies and asthma, follow the links to Allergy & Asthma Sites.

Next Vacuum Performance Aspect: Dustbag Performance and Filtration Efficiency

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