Difference Between a Pre-Filter and a HEPA Filter?

There are many different air filtering technologies, but most require maintenance to function effectively. Two of the most common technologies for filters include pre-filters and HEPA filters, and they both have hefty user bases. So what exactly are the differences between a pre-filter and a HEPA filter, and which is better?

A pre-filter and a HEPA filter aren’t alternatives you should compare to choose the best. Instead, a HEPA filter removes tiny allergens and harmful particles, while a pre-filter helps to filter larger particles. In addition, since the HEPA filter won’t have to deal with larger particles when used with a pre-filter, it lasts much longer.

In this article, you’ll learn what a pre-filter means and what it’s used for. You’ll also learn the inner workings of a HEPA filter and how it compares to the pre-filter system mentioned earlier. Then, you’ll learn the specific differences between these two technologies and which is better.

What Is a Pre-Filter Used For?

A pre-filter is a component of most air purifiers that removes large particles before getting to the main filter. The pre-filter is typically the first step in the air filtering process on an air purifier that supports them.

The pre-filter works similarly to the main filter, using a sieving mechanism. When air flows through the air purifier, the pre-filter traps the dust, hair, and other pollutants in its intertwined mesh. This mesh can filter some of the finest air pollutants, being roughly as efficient as the air purifier.

Pre-filters are typically used for filtering larger particles in the air, leaving the smaller ones for the main air filter. The main filter, usually running on the HEPA standard, should filter particles down to 0.3 microns. Doing this alone is already enough work, but they also need to remove the slightly larger particles.

With a pre-filter capable of filtering pollutants as large as 2 microns, you can relieve your main of unnecessary tasks. In addition, after the air passes through this pre-filter, the internal filter will only need to do little work, increasing its lifespan.

To justify changing your pre-filter monthly, here are some advantages of using a pre-filter:

Cheap To Replace

When you use pre-filters with your air purifier, you’ll need to clean or replace them regularly. Unfortunately, if it’s too dirty to clean, your only option is replacing them, which requires you to buy new pre-filters. Fortunately, pre-filters are usually very cheap and accessible, and some air purifier manufacturers will offer you some for free.

Replacing the filter is just as easy as most maintenance procedures, as it requires no advanced technical know-how. As long as you can follow instructions, it would help if you replaced your aging pre-filters with new ones.

Increases Your Air Purifier’s Lifespan

When your air purifier has to remove every speck of dirt in your air, it will wear itself out quickly. The only way to delay this outcome is by using pre-filters that remove the larger particles. Since your main filter will only have to deal with fine pollutants, which will certainly elongate its lifespan.

What Is a HEPA Filter Used For?

A HEPA filter is a term used to refer to any air purifier that satisfies the HEPA standard. Any filter capable of removing 99.97% of pollutants of 0.3 microns meets this standard, making it a HEPA purifier. Most of the air purifiers on the market today are HEPA-compliant since it’s the only standardized benchmark for filters.

When buying a HEPA filter, it’s essential to confirm that you’re buying one that’s marked “True HEPA.” Unfortunately, many misleading variations of HEPA over the years fool buyers into buying substandard air purifiers. Unfortunately, the EPA has no arm responsible for punishing those falsifying this standard.

Some of the inferior HEPA standards to look out for include “HEPA Like” and “HEPA Type” purifiers. These filters have failed the HEPA standardized testing but hold on to the name to look genuine. Unfortunately, while they might sell for cheaper, they’re less effective than accredited HEPA filters that meet the standard.

Here are some of the most common uses of HEPA filters and why they’re used:


An increasing number of people are adopting air purifiers in their homes to help them breathe cleaner air. Thanks to this trend, air cleaners are commonly used at homes, especially in households with people with conditions like asthma.

Air purifiers increase indoor air quality and help get rid of large and small pollutants around the home. They also remove harmful pollutants and allergens that may cause respiratory issues in humans and pets.

Hospitals and Medical Facilities

People with various illnesses leave different contaminants in the air, making the atmosphere around hospitals constantly polluted. So to keep the hospital relatively safe, it’s important to continually keep an air filter around to keep away the germs. Without this precaution, visitors to a hospital will be at risk of serious diseases, even if they’re healthy.


A workplace is usually the meeting point for many people, some with severe allergies and some carrying pollutants. So naturally, you should expect the air around the workplace to be unhealthy, and it sure is. That’s why it’s necessary to place an air filter somewhere around to keep everyone safe.

Nuclear Power Plants

Quick history lesson: HEPA air purifiers were invented in the ‘40s, and so was the standard for the filters. However, they weren’t designed to be used at home but in nuclear power plants. The idea was to prevent the workers at the plant from inhaling airborne irradiated particles, and it was pretty effective.

Thanks to its effectiveness, the air purifiers moved to hospitals and gradually made their foray into homes and offices. However, the fact that HEPA filters are now standard in homes doesn’t make it unsuitable for nuclear plants. As unbelievable as it may sound, nuclear power plants use the same kind of air filter used at home.

It’s important to note that a HEPA air filter and a pre-filter aren’t necessarily competitors. Most HEPA air purifiers can also use pre-filters to increase their lifespan, and some come with pre-filters included. With this, it’s clear that comparing pre-filters and HEPA air purifiers is an unnecessary mismatch.

What Is The Difference Between a Pre-filter and a HEPA Filter?

A HEPA filter and a pre-filter aren’t direct competitors since they’re designed to perform wildly different tasks. What’s more, you can use both of these simultaneously, even with themselves, making it unnecessary to compare them directly.

Since this article is about the differences between pre-filters and HEPA filters, I’ll try to outline them here. While there aren’t many reasonable grounds for comparison, there are still some subtle differences between the two.

Here are some of the major differences between a pre-filter and a HEPA filter:


As hinted above, comparing the effectiveness of pre-filters and HEPA filters is a mismatch, as they have different goals. HEPA filters are designed to be the primary air purifier, while pre-filters assist the primary purifier in removing larger particles. In short, there’s no real reason why a pre-filter should be as effective as a HEPA filter.

With that said, pre-filters can typically filter particles as large as 5 microns, which isn’t unreasonable. However, compared to HEPA’s 0.3 microns, you’ll notice that it’s about 16 times more effective than the former. Since you’ll typically be using them simultaneously, you shouldn’t be worrying about this.


A pre-filter has wildly different functions compared to a HEPA filter. The former was designed with another primary air purifier to enhance its effectiveness. On the other hand, a HEPA filter should be the main purifier, which a pre-filter can support.

Looking at both functions, you’ll understand why a comparison is unnecessary. You don’t buy a pre-filter or a HEPA filter; instead, you buy both to enhance the air purifier’s performance.

What Is The Difference Between a Pre-filter and a Carbon Filter?

While this article mainly compares pre-filters to HEPA filters, there’s no doubt that carbon will make a better comparison. This is because carbon air filters do the same job as mesh pre-filters, pitting them directly against each other. So, which of these secondary filtering solutions is better: pre-filter or activated carbon air filter?

Since I’ve described pre-filters earlier in this article, redefining it here will be redundant. So instead, it’s essential to look at carbon filters, which are air filters made from activated carbon. If activated carbon sounds too complicated, it’s simply charcoal, but with an extra lab touch.

The first step to making activated carbon is heating wood or other materials until the combustible part burns out. Then, the carbon is activated in a laboratory by injecting it with several chemicals to create a series of chemical reactions.

These chemical reactions create a better material at trapping dust and other pollutants than traditional mesh pre-filters. Additionally, activated carbon can filter air, water, and other fluids to remove harmful unwanted particles. When comparing carbon filters and pre-filters, carbon filters are the better option by a long shot.

Here are some reasons carbon filters are better than pre-filters and why the reverse might be the case:

Working Mechanism

The way a carbon filter removes pollutants from the air is fundamentally better than the sieving mechanism of pre-filters. In a process dubbed adsorption, air passes through the activated charcoal, with the pollutants sticking with it along the way.

This strategy is better because it not only traps solid particles; it also prevents the passage of gases and smoke. So if you’re trying to get rid of the smell of tobacco, for example, a carbon filter would be more effective.

Carbon Removes Volatile Organic Compounds (VOCs) From The Air

Volatile organic compounds are gaseous substances that quickly pass through pre-filters and HEPA filters. Since these compounds exist almost ubiquitously, you’ll need something like activated charcoal filters to get rid of them. This alone is enough reason to choose activated carbon over pre-filters.

Pre-filters Are Cheaper

Activated carbon may be miles better than pre-filters, but there’s no doubt that the latter is cheaper to maintain. So if you’re looking to save as much money as you can, you may want to get pre-filters over activated charcoal.

Pre-filters Are Easier To Maintain

Pre-filters are naturally cheaper, but they’re also easier to maintain. You can wash them to use them again in most cases until you can’t possibly wash them anymore. However, the same can’t be said for activated charcoal; how do you even wash charcoal?

With the advent of solutions like pre-filters treated with activated charcoal, you don’t even have to choose. Instead, you can buy one and get the benefits of both while inheriting some of the disadvantages as well.

How Long Do Pre-filters Last?

Pre-filters work by collecting large pollutants that clog their surface over a long period. Over time, the efficiency of the pre-filter will decline, requiring you to either clean or replace it. While most people know of that, what’s not known is how frequently they should replace their pre-filters.

The specific answer depends on what kind of pre-filter you’re using and the environment in which you’re using it. For example, pre-filters in use at a nuclear power plant will be changed more frequently than those used in the office.

If you use a washable pre-filter, you can wash it every three weeks to keep your air purifier working smoothly. Washing a pre-filter isn’t complicated; simply dipping it in a bucket of water should do the trick. If it’s machine-washable, you can also toss it into the washing machine with the rest of your laundry.

While there are many washable pre-filters on the market, you may not be lucky enough to use any. If you’re using a pre-filter that’s coated with carbon, you’ll have to replace it each time it gets dirty. Also, some air purifiers won’t let you wash and reuse pre-filters (specifically HEPA filters).

Summarily, the average lifespan of a pre-filter can range from a few weeks to months. This is because washable pre-filters can last as long as you can continue washing them without destroying the material. On the other hand, regular ones only last long enough for single-use, which is around four weeks.