What Is A Pre-Filter In An Air Purifier? (Explained!)

  • Author: Irene Batres
  • Date: September 26, 2022
  • Time to read: 7 min.
Affiliate Disclaimer

As an Amazon Associate, we earn from qualifying purchases.

Have you ever wanted to know what a pre-filter is in an air purifier?

Maybe you are shopping around and wondering why there are filters that you can remove from some models and not others.

In this article, I will cover what a pre-filter is used for, how to replace it, what a pre-filter is made of, and if it is even necessary.

Let’s get started…

What Is A Pre-Filter In An Air Purifier?

An air purifier pre-filter is the first stage of air filtration. Located before the main HEPA filter. The purpose is to capture large particles that pass through the air filter. Such as pet hair, carpet hair, lint, and large dust particles. Thus, protecting the life of the primary filter.

The pre-filter lets your air purifier work better as it has already removed the large unwanted materials. 

So, by having a pre-filter in your air purifier you can actually increase the lifespan of your main filter. 

The less work that the main HEPA filter needs to do the longer it will work for.

Larger particles in the air can clog up filters very quickly. 

This means that by having a pre-filter you reduce the amount of work that the HEPA filter needs to do.

What Is A Pre-Filter Used For?

A pre-filter is used to catch and collect the larger unwanted materials that are floating in the air. Its primary job is to help the main filter by taking over some of its work. 

So, it is not as effective as the main filter. 

However, it does not need to be. It just simply needs to catch the larger items, allowing the main HEPA filter to do all of the hard work. 

One of the main examples of what a pre-filter is used for is to catch dust. This is a very common material in the air and one that can cause allergies and illnesses. 

Therefore, the pre-filter can remove this from the air, cleaning it, and helping you to breathe better.

Other such examples of large unwanted particles are pollen and pet hair.

How Does A Pre-Filter Work in an air purifier?

How Does A Pre-Filter Work In An Air Purifier?

The simple way to know how a pre-filter work is to think of it like a sieve.

 There are small holes all over the filter. These allow small particles to pass through easily. 

However, the larger particles, such as dust, cannot. They simply will not fit through the holes.

Just like a sieve is designed to stop lumps, a pre-filter is designed to stop larger materials. By capturing the larger items, the pre-filter allows the main filter to be much finer. 

This means that it can stop and remove smaller unwanted items without being clogged up by the larger ones. 

Where Does A Pre-Filter Go?

The pre-filter is your air purifier’s first line of defense against dust and other pollutants in the air. 

So, it makes sense that it is the first filter that you will encounter when you open up your air purifier. 

It goes on the inside of your air purifier just inside the covering material. 

However, when opened it is the first thing that you will see. 

If you are still unsure, then it is typically the part that is covered in dust and possible pet hair. 

What Is Air filter Pre-Filter Material?

When it comes to the material there are two main types of pre-filters. 

  • Mesh 
  • Carbon

Which one you will need as your pre-filter will depend on the other materials used for the other filters. 

If you only need to capture the larger materials polluting the air then the mesh filter is perfect. Much like a sieve, it will stop larger materials. 

However, if you also want to stop unwanted gases then you will need to use a carbon pre-filter.

Carbon pre-filters are much more advanced. It will use activated carbon in one of three ways: powder, granules, or a honeycomb-like structure. 

In any case, the carbon pre-filter will stop both large materials and gases. 

This can be very useful if you are working in an environment with chemicals or strong odors. 

So, not only will it make the air smell nicer, but it will also make it safer to breathe.

Is Pre-Filter Necessary?

Although you do not need a pre-filter in an air purifier it is still a good idea to have one. 

This is because it will prolong the longevity of your air purifier. Simply by adding in another layer of protection your main filter will last much longer. 

For this reason, most manufacturers and companies will advise you to use a pre-filter. They are easy to install and some can even be washed by hand to reuse. 

For this reason, it is certainly worth adding a pre-filter into your air purifier. 

If you live in a particularly dusty area or you have a lot of pets that shed a lot of furs a pre-filter may actually be necessary. 

This is because you will have a lot of loose large particles in the area. These can quickly block your air purifier’s filter and cause it to break. 

So, in this instance, a pre-filter may indeed be necessary for your air purifier to function correctly.

Benefits Of Using An Air Purifier Pre-Filter

Benefits Of Using An Air Purifier Pre-Filter

There are many different benefits of using a pre-filter in your air purifier. 

The main one is that your air purifier will carry on working for much longer. This is because there is less stress placed on the main filter. 

Another great advantage of using an air purifier pre-filter is that it can remove odors from your home or office. 

So, if you have any pets, a humid room, or simply share the space with many people this can be a great benefit. 

For this, you will need to make sure that you choose a carbon pre-filter. This will stop any unwanted gases, giving you back clean, fresh air. 

This can be a particularly important piece of equipment if you work in any environment with toxic gases or strong odors. 

One example of this is people working with resin. You will want the fumes from the resin removed from the air you breathe. 

If you have any allergies then an air purifier can change your life. Here, the more particles you remove from the air the better. 

So, if you have any pets, a lot of dust, etc. then pre-filters are perfect for you. 

They will remove the unwanted hair and dust, letting the main filter do its job properly without getting overwhelmed. 

How Do You Replace A Pre-Filter?

In most cases, you will not need to replace a pre-filter. They are either made from a washable material or they can be vacuumed. 

For example, carbon pre-filters can simply be removed and vacuumed to remove any captured large particles and materials. 

To replace the pre-filter, either with another or to put it back, is simple. 

First, turn off the air purifier and unplug it from any source.

Next, simply take off the outer covering and slide out the pre-filter. 

For most air purifiers you will not need tools to do this. You should keep in mind that there may be a lot of dust and/or pet hair in the pre-filter.

I recommend placing a bag under the unit to catch any that falls.

Once you have a clean pre-filter you can simply slide it back into place. Remember which way it was facing when you took it out! 

Can You Wash Pre-Filters?

You can wash some pre-filters, but not all of them. This will depend on the material that it is made from. 

For example, any washable mesh pre-filter will be perfectly fine. 

However, any pre-filters made from activated carbon cannot be washed. You can still clean these by vacuuming them. 

If you are unsure about whether or not your pre-filter can be washed – check the manual! 

This will tell you everything specific to your pre-filter.

Keeping your pre-filter clean is very important. If it is dirty then it will not work. 

In fact, you may as well not have a pre-filter at all! So, keep your pre-filter clean and everything will run as it should.


Pre-filters are a great addition to an air purifier as they can save you a lot of money in the long run.

By catching the big particles before they reach the main filter, your pre-filter increases the device’s lifespan.

This means that your air purifier can work for many years to come. 

If you live in a home where there are a lot of contaminants in the air then a pre-filter can catch most of them and save you from allergies. Pet hair, pollen, and dust are the most common large particles in the air. 

That means that a pre-filter can make it easier for you to breathe.

However, you must remember to clean them! 

If you do not keep your pre-filter in a good condition then it will not be of any help. You can either vacuum or wash them.

Looking For Air Purifier Guides?

If you’re looking for more air purifier resources, consider checking out our other posts on air purifiers.

irene mills author of freshairdevices


Irene Batres is eager to help others create an indoor allergen-free home. She has years of experience testing out air purifiers, dehumidifiers, and other products designed to help with indoor air quality. Learn more about me.