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Hepa filter or also a carbon filter in your air purifier. What is wisdom?

There are various ways of purifying the air. A Hepa filter is currently the most used and effective way. An air cleaner with a carbon filter is also a frequently used method. But how do these filters work and how do they differ from each other? In this blog we will tell you in which situations it is best to use which filter. This way, you will know whether a Hepa filter or also a carbon filter suits your air purifier.


Why is a hepa filter useful?

The most commonly used filter in air cleaning is the hepa filter. This is the filter that is used to filter air pollution, such as fine dust and viruses, out of the air. Carbon filter air purifiers almost always contain a hepa filter as well. A hepa filter works in a slightly different way than most filters. Most filters are actually just a sieve. The air passes through the sieve. Does a particle not fit through the sieve? Then the filter will catch it. The finer the filter, the more particles you remove from the air. However, this also has a disadvantage. If the filter is finer, less air will fit through it. As a result, you will either filter less air or you will have to use a heavier engine. Neither of these are attractive options. The Hepa filter has found a solution for this.


How does a Hepa filter work?

Every good air cleaner, carbon filter or no carbon filter, needs a Hepa filter. A hepa filter works with different layers of fibres. These are actually long threads. By placing these over each other in a random manner, small holes are created. These filter the air. The special thing about a hepa filter is that it filters particles that are smaller than the holes in the filter. A hepa filter works by two different methods. The barrier effect is the simplest. The holes between the fibres are simply too small for some particles and therefore they get stuck. This is in fact normal filtration. The second effect is called the inertia effect. Because the fibres are laid on top of each other in a random manner, the air has to make many bends and twists. Particles that fit through the holes but do not make all the turns fast enough therefore collide with the fibres and remain stuck to them. In this way, a hepa filter with a small motor already has a lot of capacity and still filters the small particles and viruses out of the air. After a while the filter gets clogged by all the filtered particles. Therefore, it is recommended to replace a hepa filter between six months and one year.


carbon filter air purifier


Different levels of hepa filter

The name HEPA is a protected name. This means that a filter has to meet certain standards in order to call itself a HEPA filter. In Europe there are two categories of HEPA filters: H13 and H14. An H13 filter must remove at least 99.95% of the particles smaller than 0.3 micrometre. For comparison, that is more than 50 times smaller than a hair! If the filter’s performance rises above 99.99%, it may call itself H14. Is the filter so fine that it removes more than 99.9995% of the dirt? Then it is an Ultra Low Particulate Air (ULPA) filter. For most situations, this difference hardly matters anymore. Especially cleanrooms in hospitals and laboratories use ULPA filters. Again, the finer the filter, the less air will fit through it. Carbon filters for air cleaners do not have these qualifications. They work in a different way.


What about Active Ion Hepa filters?

Sometimes you also have the option of AIH filters. This is a sub-type of Hepa filters. They are also called Active Ion Hepa filters. These filters focus less on the barrier effect and more on the inertia effect. This filter works with ionised fibre threads. Because of this, they attract more air pollution. You therefore need fewer small holes to achieve the same level of filtration. This makes air cleaners with AIH filters more powerful and more economical.


Carbon filter air purifier

If a Hepa filter works so well, why do you need an air purifier with a carbon filter? The answer is that carbon filter air purifiers and hepa filters are suitable for other things. With hepa filters you remove air pollution. These are particles that we inhale and cause various health problems. But there is another class of air pollution, and a hepa filter does nothing about it. These are gases and odours. A normal filter that works like a sieve does not stop gases, however small they may be. Still, certain gases are very annoying or harmful and some are even poisonous. Ozone is a good example of this. Foul odours are also never pleasant. With a carbon filter, an air purifier does stop odours and gases. This way, you keep your indoor climate comfortable and healthy. However, you should never use a carbon filter on its own. Air pollution such as fine dust is not stopped by a carbon filter.


carbon filter air purifier


How does an air cleaner with carbon filter work?

A carbon filter in an air purifier does not work with ordinary filtration. This type of filter works by adsorption. This is different from absorption! In this case a liquid absorbs another liquid. Think for example of mixing lemonade syrup with water. Adsorption is the process whereby gases and other small organic substances bind themselves chemically to the carbon. In this way, they disappear from the air. Many filters advertise themselves as so-called “active carbon”. This means that the carbon is processed into very small particles. Because of this the carbon has a much larger surface than normal carbon. One gram of activated carbon covers up to 3000 metres of surface! This is important, because with more surface area the carbon binds more polluting gases. This makes it more effective and longer lasting. After a while, however, the carbon becomes saturated and is used up against gases and odours. To maintain a high level of effectiveness, it is therefore important to replace the carbon filter in the air purifier every year.


I already have a filter in my ventilation system, is that a hepa filter?

Many ventilation systems also use filters. However, these are rarely hepa filters. This is because air purification and ventilation have two different goals. With air purification you want to clean the air. Fine-meshed hepa filters are essential for this. Ventilation aims to supply outside air and remove inside air as much as possible. Fine-meshed filters work against this. After all, the finer the mesh of the filters, the more energy it takes to work air through the ventilation system. This is why coarse filters are the norm in ventilation systems. A combination of ventilation and air cleaning therefore works best. You combine the fresh air of a ventilation system with the circulation of an air cleaner that further purifies the air with its Hepa filter and/or carbon filter. You can refine the circulation of an air cleaner to such an extent that the entire indoor air is reached. This way, you ensure that all nooks and crannies in your office or living room have clean air.


What about ionisation?

Many air purifiers nowadays offer the option of adding ionisation. This makes the filtering process more effective than with just a hepa filter and kills viruses and bacteria faster. Unfortunately, most ionisers also release ozone. This is a toxic gas that has its own health problems. A carbon filter in the air cleaner removes the ozone again. Some air cleaners use ionisation before the filter. This method creates hardly any ozone and is therefore a good alternative. You can read more about ionisation and ozone in this blog.


Need advice or more information?

Which filters you need naturally depends on your situation. Do you live in a busy city next to a motorway? Then good hepa filters are essential. Are you in an office where a lot of printing takes place? Then carbon filters are a good addition. Do you already know which filters you need? Then visit our product page. Do you still need tailor-made advice? Call us at +31 (0)20 646 4028 for personal advice without commitment!