What Is a Pre-Filter in an Air Purifier? Benefits & Limitations

In Brief: What Is A Pre-Filter?

The prefilter is the first layer of filtration in a multilayer filter. It is a mechanical filter that filters out the larger airborne impurities that pass through the purifier before it reaches the main filter.
Its objective is to remove the coarse particles that enter the air stream of the purifier. It also improves the life span of the main filter.

Nowadays, air purifiers come with multilayer filtration mechanisms.

If you are wondering whether you need to buy air purifiers with a prefilter in them, then you have come to the right place.

We will now discuss Pre-filter, its types, benefits, and limitations in detail.

This article will give you an idea about Prefilters and help you decide whether you need to buy an air purifier with a prefilter or not.

What is a Pre-filter?

Prefilter is a filter that traps impurities that are larger in size before they reach the main filter. It is composed of materials like fiberglass, fabric, or paper product in the form of sheets.

It is used in both air and water purifiers. In the air, the purifier filters hair, pollen, dust, insects, etc., and in water, it filters sand, fiber, etc.

What are Pre-filter Types & How they Work?

Prefilter is the first layer in the air purifier that uses a multilayer filtration mechanism.

The prefilters are classified based on washability and the material used. Let us now discuss the types of prefilters along with their working principle in detail.

Washable prefilters – Washable prefilters are washable and can be reused multiple times. However, it is a bit costly.

Non-washable prefilters – Non-washable prefilters can’t be washed and must be replaced every three months (use and throw) and are comparatively cheap.

Fiberglass filter – Fiberglass filter is made up of spun glass reinforced with metal grating. It filters the coarse particles like lint, sand, dust, hair in the air before reaching the main filters. It is a non-washable type of prefilter. Its MERV (Minimum Efficiency Reporting Value) rating is 1-4.

Pleated fiber filter – Pleated fiber filter is the next version of a fiberglass filter with high air resistance. It has a better dust-removing capability than fiberglass however, it reduces the efficiency of the purifier gradually if not maintained properly.

Both washable and non-washable types are available and are suited for people with respiratory ailments. Its MERV (Minimum Efficiency Reporting Value) rating is 10-13.

Some of the applications of prefilters are furnace (domestic and commercial) and HVAC units.

Carbon prefilters – Carbon prefilters are used for removing larger particulates and odor. HEPA (High-Efficiency Particulate Air) filter is used as the main filter in this air purifier.

In general, the prefilters are situated upstream of the main filter. It is the first line of defense against the airborne impurities that enter the purifier.

When the air enters the prefilter made up of fabric or fiberglass, the larger particles get trapped in between the spaces of the prefilter.

The main filter purifies the smaller particles that have escaped from the prefilter layer. The purified air is then emitted into the atmosphere.

The image of a prefilter filtering the large impurities is shown below.

Benefits of using a Pre-filter

Now let us discuss the benefits in using prefilters in air purifiers.

Improves Air quality – Prefilters traps large particulates like dust, pollen, insect bodies, etc., and improve the overall air quality.

Increases lifespan – Prefilters filter the larger-sized particles and increase the life span of the main filters like HEPA (High-Efficiency Particulate Air) filter or Activated Carbon filter in the air purifier.

Improves filtration – Prefilter filters the larger particles leaving the main filters like HEPA (High Efficiency Particulate Air) filters to filter smaller particles. Thus, reducing the pressure on the motor of the main filter and improving the filtration rate.

Cost-effective – Buying filters with a prefilter is said to be cost-effective from the time of buying the product till its disposal.

Single investment – Prefilters are washable and reused multiple times. Hence, it is a single investment, and there is no need to spend later for a replacement.

Limitations of Pre-filter

Benefits and limitations are the two sides of the same coin. Now let us discuss the limitations of using prefilters in air purifiers.

Noise – Prefilters adds another layer to the air purifier. It produces noise as it reduces the airflow.

Energy consumption – If the prefilter is not cleaned regularly, the impurities accumulated in the prefilter layer will impose more pressure on the motor that regulates the airflow of the purifier. Thus, increasing the energy consumption of the motor.

Maintenance requirements – Prefilters must be washed and maintained regularly. In case of poor maintenance, the efficiency of the purifier will decrease.

Limited in what they can remove  – Prefilters cannot trap smaller particles, microbes, odor, etc., hence, they must be used, along with other filters. Prefilter alone is ineffective against airborne impurities.


Thus, Prefilter is the first filtration layer in multilayer air purifiers used to remove larger impurities.

It increases the life span of the main filter in the air purifiers by removing the larger contaminants before it enters the main filter.

It aids in improving the air quality and the health of the people who breathe in the air emitted by these purifiers.

From the above article, you must have a clear idea of the Prefilters and their pros and cons. In case of further information, please type in the comment box below or reach us through email.

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