Air Purifier Pre-Filters – Everything You Need to Know

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Air purifiers are a great option for increasing the air quality inside your home. An air purifier’s HEPA filter is efficient at removing microscopic particles such as smog and smoke. However, HEPA filters tend to get clogged up by larger particles such as dust and pollen.

Using a pre-filter in your air purifier is essential to maintain the health of your air purifier’s main HEPA filter. By doing so, you’ll extend the life of the HEPA filter, saving you money in the long run.

In this article, I’ll explain what a pre-filter is and discuss its benefits. I’ll also explain how to maintain your air purifier’s pre-filter so it’s always performing at its best.

What is an air purifier pre-filter?

An air purifier pre-filter removes particles from your room’s air before the main HEPA filter. The pre-filter is located upstream of the main filter, so airflow will go through the pre-filter before it touches the main filter.

The pre-filter is not as effective as the main filter at removing particles from the air. That doesn’t matter, since removing tiny particles from the air is not the purpose of the pre-filter. 

Pre-filters remove large particles from your room’s air so the main HEPA filter doesn’t have to. We’ll explain more below.

Benefits of using an air purifier pre-filter

Using an air purifier can be expensive when you factor in the costs of replacing air filters. The use of a pre-filter addresses that issue.

Pre-filters capture dust

Air purifier pre-filters capture dust and other large particles. As the first line of defense, they filter out many particles before the particles get to the HEPA filter.

Air purifier pre-filters even capture particles such as pet hair and pollen. This is a huge benefit because pet hair and pollen can quickly clog up a HEPA filter.

Pre-filters extend the life of the main HEPA filter

Using a pre-filter in your air purifier will help prolong the life of the HEPA filter. Since the HEPA filter has such a fine mesh, it tends to get clogged quickly.

Using a pre-filter will block out large debris from getting stuck in the HEPA filter. This will give your HEPA filter more room to capture the microfine particles that it’s designed to capture.

Pre-filters are easy to clean and cheap to replace

Many air purifier pre-filters can be cleaned and reused over and over again. A typical reusable filter just needs to be sprayed down with water to remove particles.

If you don’t have a reusable pre-filter, that’s okay too. Air purifier pre-filters are made of less efficient filter material. So they tend to be much cheaper to replace than HEPA filters. You can get pre-filter material at reasonable prices, so replacing one won’t hurt your wallet.

Should you use an air purifier pre-filter?

Yes, you should use a pre-filter in your air purifier as long as the manufacturer allows it. In fact, most air purifiers come with pre-filters, so chances are that your air purifier already has one.

Reduced maintenance costs are the main benefit of using a pre-filter in your air purifier. Replacing HEPA filters are the primary ongoing cost of using an air purifier. Using a pre-filter helps keep maintenance costs down by prolonging the life of the HEPA Filter.

If your air purifier uses a replaceable pre-filter, then the cost of the pre-filter will be much lower than the HEPA filter. So it makes sense that the pre-filter takes the brunt of the dust as much as possible.

But you may not even need to replace your air purifier’s pre-filter. Many air purifiers use washable and reusable pre-filters.

In this case, your only job is to clean or replace the pre-filter regularly. 

How often do you need to change an air purifier pre-filter?

The air purifier pre-filter should be cleaned or changed at least every 30 days. If your house is dusty or you have pets, you will need to change your pre-filter more often.

Pre-filters are great because they capture dust, pollen, and hair. But those particles will build-up on the pre-filter over time. Eventually, the pre-filter needs cleaning or replacement.

A good rule of thumb is to check your air purifier’s filters once every week. If the pre-filter is dirty, then it’s time to clean or replace it.

Why it’s important to change your air purifier’s pre-filter

Changing your pre-filter ensures that it stays free and clear of debris that impedes airflow. A dirty pre-filter will reduce airflow through your air purifier. Lower airflow through your air purifier will reduce its filtration efficiency. 

A dirty pre-filter will also cause the fan motor to work harder and use more energy to produce the same amount of airflow. So increased electricity costs are another downside of a dirty pre-filter.

There are also reusable pre-filters for air purifiers. These don’t need to be replaced, you can just clean them instead.

How to clean an air purifier pre-filter

Cleaning an air purifier pre-filter is like cleaning other types of reusable filters.

First, you’ll need to ensure that the pre-filter is washable. To check if your pre-filter is washable, the best thing to do is to consult the manufacturer’s manual. Some pre-filters are disposable and should not be cleaned and reused.

Filters are usually washable if they are made of a certain material:

  • Washable: Generally, pre-filters that are made of polyester are washable. If your air purifier has a mesh screen, then those are washable as well.

  • Not washable: Pre-filters that are made of cotton or fiberglass are generally not washable.

To clean your air purifier’s pre-filter, follow these steps:

  1. Turn off and unplug the air purifier. Ensure that the air purifier is off and disconnected from any electricity sources.

  2. Open the filter cabinet and remove the pre-filter. You won’t need any tools to remove the pre-filter in most air purifiers. Keep in mind that the air purifier will have lots of particles lodged in it. It’s a good idea to place your air purifier in a plastic bag so dust doesn’t get all over the place.

    Pay attention to the orientation that the pre-filter is placed inside the air purifier. You’ll need to put the pre-filter back in the same direction when you’re done.

  3. Wash the pre-filter. Bring your pre-filter outside. In most cases, you can shake the dust off or clean the pre-filter with a vacuum. The large particles that get stuck in a pre-filter tend to be easy to remove.

    Alternatively, you can spray your pre-filter out with a garden hose. Be sure that you spray the pre-filter in the opposite direction that air flows. This method is called backwashing and will force particles off of the filter.

    For an excessively dirty pre-filter, you may need to scrub it with soap and water. If you scrub your pre-filter be gentle so it doesn’t get damaged. DO NOT wash the pre-filter in an automatic washer or dishwasher.

  4. Dry the pre-filter. Allow the pre-filter to completely dry before putting it back in your air purifier. The pre-filter must be air-dried. DO NOT use heat or an automatic dryer to dry the pre-filter.

  5. Replace the pre-filter. Put the pre-filter back in the filter slot in your air purifier. Be sure that it latches and is placed in the same orientation that it was before.

What about air purifier carbon pre-filters?

Carbon pre-filters serve a different purpose than simply filtering out particles. Carbon pre-filters specialize in eliminating odor particles so your room doesn’t have any bad smells.

Many odor particles are too small to be captured by an air purifier’s HEPA filter. HEPA filters are excellent at capturing particles as small as 0.3 microns. However, volatile organic compounds (VOCs) are often much smaller than 0.3 microns. VOCs are so tiny that they can slip right through an air purifier HEPA filter.

So what are volatile organic compounds anyway? VOCs are gases that are emitted from solids or liquids. Even things in your own home can emit VOCs. Cleaning products, air fresheners, and pesticides are some household items that emit VOCs.

The main issue with VOCs is that they can cause health issues. Eye, nose, and throat irritation are some of the common effects. Exposure to VOCs can also cause headaches and nausea.

Fortunately, using a carbon pre-filter in your air purifier helps to neutralize VOCs. As VOCs flow through a carbon filter, they are trapped by the filter through a process called adsorption. 

The more porous the carbon filter, the better. This is because there is more surface area for the VOCs to adhere to in a porous carbon filter.

Using a carbon pre-filter in your air purifier ensures that you have some level of protection against VOCs. If you notice that your air purifier is unable to eliminate odors from your home, it’s time to try out a carbon pre-filter.

Hi, my name is Trey Lewis and I’m the founder and chief editor at HVAC Training Shop. My goal for this website is to help homeowners troubleshoot and maintain their home’s HVAC systems. Whether it’s changing an air filter, troubleshooting a blower motor, or just buying a new humidifier, I want to make sure that you’re covered.

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