HEPA filters are available as attachments for air conditioners, air purifiers, and other air filtration devices. They provide an additional layer of filtration, specifically aimed at capturing small particles. Not every particle filter is a HEPA filter though – there are some specific standards that must be met. Using a HEPA filter can be very helpful in situations where removing a high percentage of particles from the air is important.

What Does HEPA Stand for?

HEPA means “High-Efficiency Particulate Air” and is a common industry standard for air filters. For a filter to qualify as a HEPA filter, it must remove a specific percentage of particles of a given size from the air that passes through it. That percentage differs between regions but is usually above 99.95%. In the United States, the threshold is even higher – HEPA filters must be able to remove at least 99.97% of the targeted particles.

The performance of HEPA filters is usually measured specifically for particles with a size of 0.3 microns. While most people assume that HEPA filters work better above this level and worse below it, the reality is a bit more counterintuitive. That’s because particles start to behave very differently at that scale, and very small particles don’t follow the same patterns of motion as larger ones.

How Are Particles of Different Sizes Filtered?

HEPA filters feature a fine fibre mesh designed to capture larger particles. That mesh is specifically designed around the physical properties of 0.3-micron particles. Why? As it turns out, 0.3 microns is a special threshold when it comes to filtering particles from the air. Particles larger than that usually don’t make it into the filter in the first place, getting blocked by the initial layer of fibres.

On the other hand, smaller particles are captured by having them run through a “maze” of fibres. The idea is to reduce their velocity enough that they would eventually come to a halt inside the filter. The chaotic motion patterns of those particles make it very likely that they would eventually hit a fibre and stop completely before reaching the other end of the filter.

Particles that are exactly 0.3 microns (or close to that size) tend to be more challenging for HEPA filters. They’re small enough to pass between the filter’s fibres but still too large to be effectively captured through diffusion. That’s why HEPA filters are rated for their performance against particles of this specific size. The performance charts of most HEPA filters show a noticeable dip right around the 0.3-micron area, with effectiveness climbing steeply on the left and right sides of that point in the chart.

Do HEPA Filters Require Maintenance?

Most HEPA filters are designed to operate without any maintenance, including cleaning. In fact, cleaning a HEPA filter might cause damage to its delicate fibres, and is only recommended if the filter’s manual explicitly allows it. Even then, you should never use any rough fabrics or abrasive chemicals to clean your HEPA filter. Simply run it under cold water and allow it to dry completely before reinstalling it.

Once your HEPA filter has accumulated too much dust, it will need to be replaced. Most models can last for about a year under normal conditions. In some cases, you might need to change your filter more often, such as when using it in particularly dirty environments. When in doubt, always follow your manufacturer’s recommendations and don’t try to gauge the filter’s state visually.

Who Can Benefit from a HEPA Filter?

HEPA filters are useful in a variety of situations where advanced purification of the air is required. Parents who’ve recently welcomed a new child into their households are often advised to install HEPA filters for at least the first few months of the baby’s life. Reducing the number of potential irritants in the air is not only useful for children with allergies. It can improve the quality of the baby’s life significantly during that sensitive early stage of its life.

People suffering from allergies and conditions like asthma can also benefit from additional filtration of the air in their homes. In some cases, a HEPA filter might even enable a person to live under the same roof with animals they are normally allergic to. This rarely works in more severe cases but is still an option worth considering for people with mild allergies.

Finally, many smokers have started to install HEPA filters in their homes over the last decade. Combined with a carbon filter, this can be an effective way to minimize the unpleasant odours associated with the habit and can help preserve the home’s interior over the years.

When Is a HEPA Filter Not Helpful?

There are some situations where HEPA filters don’t help much, if at all. Dealing with bacteria and other microorganisms is a common example. A HEPA filter only catches bacteria, it does nothing to kill them. This makes it unsuitable for situations where air must be disinfected and not just purified.

In some cases, HEPA filters can actually make the situation worse if they are not paired with an appropriate purification system that kills microorganisms. If the filter is not replaced often enough, bacteria will start to accumulate and might even thrive in the environment of the filter’s fibre mesh. That’s why HEPA filters should only be used in combination with additional air purification whenever microorganisms are a major concern.

This is particularly important for people suffering from specific allergies. Dust and mould allergies can be exacerbated by the incorrect use of a HEPA filter if the air is not run through any separate purification methods.

When used correctly though, HEPA filters can improve the overall effectiveness of air purification systems. Clearing the air of extra particles allows it to be more thoroughly cleaned by systems targeting bacteria and other microorganisms. That’s why HEPA filters are commonly used with dedicated air purifiers for the best results. When in doubt, consulting a specialist before investing in a HEPA filter is a must.

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