What is a pre-filter and why do you need it?

In this article, we will cover the topic of air purifier pre-filters. If you have ever wondered what a pre-filter is and what its purpose is, keep reading to find out the answers to all your questions on this topic.

Let’s find out what is a pre filter air filter, what are the main types of pre-filters, how carbon pre-filter is different from mesh one etc.

What is a pre-filter and why do you need it?

Why do we need pre-filter air filter?

In domestic ventilation systems, air filtration is necessary to protect against dust particles and various impurities from entering an apartment or office; good filtration protects the interior decoration of the room from pollution, and a person from dust entering the lungs.

With semi-industrial and industrial ventilation, an air purifier with a pre-filter protects the system itself from coarse dust from contamination.

In industry and medicine, air filters are often used to maintain a given air purity.

Sometimes, purification of the air emitted from the premises is required, for example, in bacteriological centers or at nuclear power plants.

What is a pre-filter and why do you need it?

What is a pre-filter?

A pre-filter is an air filter that removes large contaminants in the form of dust, hair, and so on. The pre-filter is the first step in purifying the air with a purifier. The pre-filter prevents clogging of the main filter inside an air purifier, so they can more effectively rid the air of microscopic contaminants.

Such pre-filters are found in many air-purifiers that are installed at home, in offices, transport, and so on.

Pre-filters are within the first stage of air filtration process. They come in many shapes and types, and each manufacturer has their own pre-filter.

The pre-filter usually does not filter anything. Pre-filters’ main purpose is to protect the HEPA filters in an air purifier from being quickly contaminated and therefore prolong their service life.

What are air purifiers?

All filters of air purifiers according to the international classification are divided into three classes of efficiency: coarse degree of purification, fine degree of purification, high efficiency purification (HEPA).

Depending on the filter materials and technologies used, there are: coarse or fine mechanical filters, electrostatic filters, carbon filters, sponge filters, oil filters, HEPA filters, photocatalytic filters, and others.

Coarse filters made of large-mesh materials or fibrous fabrics retain particles larger than 10 microns (fluff, dust, wool or other large contaminants). Such a filter has a long period of use. It must be washed or vacuumed when dirt accumulates. Change in case of wear – once every 6 months.

HEPA filter

For more efficient air purification, you can use devices with mechanical HEPA filters. These filters are corrugated and made of fibrous material. An air purifier that uses such filters draws in air with the help of a fan. Thanks to this, the air almost completely gets rid of fungi, dust, and pollen from plants.

The vast majority of modern air purifiers have HEPA filters (High Efficiency Particulate Air) installed, as do most vacuum cleaners. Their efficiency is high, but it should be remembered that the results of air purification in real living conditions may differ from the results obtained in the laboratory.

Main HEPA air filter and air purifier pre-filter are not the same thing. Pre-filter is the first stage filtration that captures larger particles, while HEPA are the main air filters which trap microscopic pollutants.

It is important to note that HEPA filters are capable of retaining both solid particles and even large ones. However, when left to do this, the HEPA air purifier gets dirty pretty quickly, and it may be necessary to change the filters more frequently than would be the case with built-in pre-filters. The pre-filter is much easier to maintain and clean. This means more savings and no need to get pre-filter replacements too often.

Types of pre-filters

There are two main types of pre-filters: a mesh pre-filter and a carbon filter.

Mesh pre-filter

Mesh pre-filter sieves large particles. This air purifier pre-filter is made of small pores through which air flows, but large particles of dust, dirt, or hair do not pass through. It is an air purifier unit that traps contaminants and protects the main filter.

The best option would be an air purifier with its own dedicated mesh pre-filter that works to protect the main HEPA filter and activated carbon pre-filters.

Carbon Pre-filter

These filters are used to finely purify indoor air. Activated carbon filter is able to rid the environment of various harmful impurities and even trap gaseous pollutants and volatile organic compounds.

It is worth noting that they are unable to qualitatively purify the air from ordinary dirt and bacteria, so it is recommended to install an additional pre-filter for this task. However, the carbon filter will work as a dual pre-filter and odor remover.

Unlike the previous type, devices with carbon pre-filter elements will not work well in conditions of high humidity. Due to this very moisture, the coal will get wet and lose its cleansing ability.

Activated carbon filter air purifiers are indispensable in everyday life and in small industries. The principle of operation is as follows: the air flow that needs to be cleaned first passes through a pre-filter, trapping particles of dust and chemical vapors. This makes it possible to extend the use of coal in air-purifier.

Further, the air mass passes through the filter cylinders, in which the carbon layer is located. It comes out purified from 99% of impurities and chemical compounds. The effectiveness of such activated carbon filter depends on the area of ​​the processed room.

The most popular models of household air purifiers are compact and carbon cassette filters. The first are U-shaped plastic frames with a carbon layer inside. Charcoal cassette filter—a stainless steel frame into which charcoal filters are inserted.

Although effective in combating unpleasant odors and dust, the carbon pre-filter in an air purifier need to be replaced periodically. Filtered microscopic dirt, dust, and other harmful substances settle in the pores of activated carbon, and it begins to crumble over time. To prevent this, change the pre-filter in the air purifier in time.

Washable pre-filters

This is the most practical type of filters because you can wash pre-filters of this kind in the washing machine. Most often, such filters themselves are made of fabric, so it’s easy to wash a dirty pre-filter without having to replace it with a new one too often.

Perhaps you will also be interested to read Purified water vs distilled water for humidifier.

Importance of air-purifying

Air filters are of great importance in the operation of the ventilation system. Their main task is to purify the air entering the room and protect the elements of the ventilation system from contamination, and in some cases to purify the exhaust air at the outlet of the system to the outside.

Thus, not only the purity of the air that a person breathes in the room depends on them, but also the efficiency of the ventilation system as a whole, as well as the quality of the air entering the environment from the room.


How pre-filter air filters affect air?

Research that was undertaken on enhancing indoor air quality with pre-filter air filters showed the following. The air purifier in which the air was filtered first by a coarse pre-filter, followed by a Rota-filter, have the capacity to capture substantial amounts of airborne dust particles and airborne allergens.

What is a pre-filter used for?

Pre-filters do two things: they capture particles that are too large and extend the life of the main internal filters. Pre-filters protect the main filter, so they can do their job and get rid of microscopic particles and thus be more useful.

Is a pre-filter necessary?

A pre-filter is of course not strictly required, but it will save you money in the long run, and the air you breathe will be cleaner. The main filter may not be able to trap large contaminants and will simply work worse and wear out faster. The pre-filter will protect it by ridding the air of large particles.

You would want to at least choose an air purifier with pre-filter made of activated carbon material, because it levels up filtration efficiency of your air-purifying device.

Pre-filter protects HEPA filter or any other filters that are built in your filtration system.

What does a pre-filter look like?

These are the simplest filters used in air cleaners. You can pick a simple filter consisted of a conventional fine mesh and are used as pre-filters. Designed to remove large dust particles, animal hair.

Air purifier pre-filter can look different depending on the type and manufacturer that you pick, it has to be capable of capturing large particles.

Regardless of the purpose and class of cleaning, filters in the bulk have a similar design. They consist of a body and a removable cassette. The filter box is mounted in the ventilation system, and replaceable filter cassettes, if contaminated, must be replaced.

To make changing the filter cassettes easy, there is a snap-on cover in the housing. For easy installation, filters installed in circular duct systems are usually made with round branch pipes, the size of which is equal to the connecting diameter of the duct. Rectangular filters have an inlet that is equal to the size of the cross section of a rectangular duct.

What does pre filtration mean?

Pre-filtration means preliminary filtration, which is a part of an air purifying equipment that is used to capture large particles.

Air purifier pre-filter means high air quality. It gets rid of large particles, so the main filter like HEPA filter air purifiers can clean your air more efficiently.

Air purifier with pre-filter is useful for collecting large particles

Are there disadvantages associated with pre-filters?

In some devices, using a pre-filter can be seen as a disadvantage. This is most especially in the case of a weak device that does not have sufficient airflow. In this case, the air filter is usually combined with a carbon filter, because the carbon filter traps what the pre-filter cannot.


You may have been in doubt and ignored the pre-filter when searching for an air purifier, because you probably didn’t know what is a pre-filter; after reading our article, you know that the pre-filter is needed not only to filter the air but also to extend the life of the primary filter (HEPA filter).

We highly recommend you clean and maintain the pre-filter as often as possible, as this will save the HEPA filter and reduce maintenance costs, as the HEPA filter is not cheap.

The prefilter is an important part of the filtration system, as it does the most “dirty” job of softening the air before it passes through the main air purifier filter; it traps solid particles to let internal filters deal with small dust particles. It is best to check with the suppliers before buying whether the air purifier has a built-in pre-filter.

Carbon filters are also a useful air purifier unit, but they are not able to filter large contaminants, so it is good if they are supplemented with a mesh pre-filter.

Now you know what is a pre-filter, how it is different from HEPA filter, how air purifier pre-filter functions and so on.

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