Heavy dust on the HEPA filter of an air purifier taken out for cleaning

How do I clean a HEPA filter?

The HEPA filter is effective in removing particles such as dust, allergens (pollen, dust mites) and mould spores from the air, but it loses its effectiveness when it becomes clogged with debris. Once saturated, it releases the pollutants trapped on its surface back into the air. Because it is used all the time, you need to clean or change your HEPA filter regularly to effectively clean the air in your home.

Cleaning your dusty HEPA filter is not as easy as it sounds. In this article we will look at different types of HEPA filters to see if they can be cleaned and if so, how to do it properly so as not to damage them.

What is the HEPA filter made of?

The HEPA filter, or high efficiency particulate air filter, is defined by its ability to filter out particulate matter. To meet the HEPA standard, it is estimated that a filter must be able to remove 99.97 % of particles as small as 0.3 microns from the air passing through it.

In practice, the HEPA filter is mainly made from materials such as coarse glass fibres, plant fibres or synthetic fibres. These fibres are randomly entangled and compressed into sheets of paper. The sheets are then pleated to increase the surface area through which the air passes and mounted on a frame made of cardboard, plastic, wood or metal.

Some manufacturers sometimes add other elements to a HEPA filter, such as a pre-filter to filter out larger particles, activated carbon to help remove volatile organic compounds (VOCs), or a chemical treatment to make the particles stick to the fibres.

Where can we find it?

Originally developed to remove radioactive particles from the air, the HEPA filter soon found itself used in industrial and research facilities. Today it is found in many consumer products such as air cleaners, hoovers, cars, ventilation and air conditioning systems.

Good indoor air quality is a real concern for people with allergies or sensitive immune systems. Particles such as dust mites (and their droppings), mould spores and other airborne allergens can trigger allergies or asthma. This is why the HEPA filter is used to clean polluted air. We recommend its use in our selection of air purifiers to combat allergies.

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Can a HEPA filter be cleaned?

A HEPA filter is designed to filter only particles (not volatile organic compounds such as those in cigarette smoke) from the air. However, by accumulating particles (dust, etc.), the HEPA filter provides all the conditions for mould growth according to a Korean study. These moulds can then potentially be released into the air, making it important to clean or change your HEPA filter regularly.

But can you clean a HEPA filter? If it doesn't say "washable" or "permanent" the answer is no. You can rinse the filter in water, tap it to release excess dust or vacuum it, but this can potentially damage the fibre mesh that filters out particles. Even if the filter does not appear damaged, some of the fibres will be broken or stretched. Your filter will end up looking fairly clean, but it will no longer do its job of filtering properly.

What allows a HEPA filter to purify the air of its particles is the coherence of the "weaving" of the glass fibres that compose it. If the fibres are stretched or torn, this can create gaps in the filter large enough for particles to pass through. The integrity of the frame and its seal are also important. A frame with damaged seals can allow air to flow around the filter instead of through it.

If the filter is marketed as "washable" or "permanent", then it can be washed or cleaned. Please note, however, that there is no standard for washable HEPA filters. Furthermore, no studies have been carried out to test the functioning of these filters after cleaning.

Why is cleaning an air filter a bad idea?

Close-up of a HEPA particulate filter

As we have seen together, cleaning a HEPA filter will almost certainly damage the extremely fine mesh of fibres that make it up. But even if you are 100 % sure that the filter will not be damaged, there are other reasons why cleaning a HEPA filter is not a good idea :

  • Cleaning a filter is a dirty job. Unless you leave your home to clean it, there is a good chance that it will release pollutants into the indoor air. These reintroduced pollutants can also include microbial growth that has developed on the filter. Cleaning your filter outside will not prevent you from inhaling particles during cleaning, which can trigger an allergic reaction.
  • If you clean your filter with a hoover, it should also have a HEPA filter, otherwise it will not be able to retain the particles from the dirty filter and will disperse them in the air.
  • The filter should be dry before use, as a wet filter could allow mould to form on its surface. Due to the fine mesh, a HEPA filter will take a long time to dry (manufacturers recommend at least 24 hours).

How do you clean a HEPA filter if you have to?

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As a general rule, it is recommended to replace the HEPA filter, not to clean it. But if you absolutely have to clean a HEPA filter, there are two ways to do it. The method you use depends on the type of HEPA filter you have:

  • A washable HEPA filter should be cleaned by rinsing it with cold water (Do not use detergents and do not put the filter in the dishwasher or washing machine). Be careful not to touch the filter fibres, but only let them come into contact with water. Allow the filter to dry completely before reinstalling it. Some filters have special instructions: refer to your appliance manual before cleaning.
  • A permanent HEPA filter must be cleaned gently with a hoover to remove dust and debris from its surface. Water should not be used on these types of filters.

In all cases, we recommend that you dismantle your appliance externally before removing the filter. Some filters can be difficult to remove. It would also be a pity to release stored dirt and grime into the air by emptying it into your household rubbish bin.