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Carbon Air Filters | How They Work (Simple Explanation)

When it comes to odors and harmful gaseous compounds, common air filters just don’t do the job. Carbon air filters, on the other hand, are very effective at removing these pollutants.

When compared to common air filters, they are more effective at removing some compounds than others. For this to make sense, the process of activating and compressing carbon must be understood as well as adsorption.


Carbon air filters use activated and compressed carbon to trap gases and odors onto the surface of the carbon in a chemical process called adsorption.

What Are Carbon Air Filters?

Carbon air filters are made of compressed, activated carbon and are used to reduce odors and the concentrations of volatile organic compounds (VOCs). 

Activated carbon (charcoal) has gone through a process that has enhanced its ability to trap gases. The process includes the carbon being injected with hot air, carbon dioxide, or steam. 

This process creates a lattice of pores in the carbon. This increases the surface area of the carbon and the pores act as nets for VOCs and odors.

Compressed means that the carbon was pressed into a thin sheet. This process increases the surface area even more and, therefore, increases the filtering ability of the sheet of carbon.

How Do Carbon Filters Work?

Although carbon air filters have pores through the process of activation, the size of the pores does not matter because carbon filters filter by adsorption, not size. 

However, the surface area of the carbon filter does matter, and introducing pores increases the surface area.

The more surface area there is, the more molecules can be trapped on the surface of the carbon filter. This is because adsorption is utilized by carbon air filters rather than absorption. 

How carbon air filters work

Now, I haven’t just been misspelling absorption. Adsorption differs from absorption because the gas molecules are trapped on the surface of the filter rather than inside the filter. This is why the surface area is so important.

Explained in chemistry terms, pollutants are stuck on the surface of the carbon filter because of van der Waals and electrostatic forces between the pollutants and the carbon filter. These attractive forces keep the pollutants stuck here for an extended period of time.

What Is Removed by Carbon Filters?

Carbon air filters remove VOCs from the home. These are a variety of chemicals, including those used in petroleum fuels, hydraulic fluids, and paint thinners. 

VOCs can cause both long and short-term health effects, which is why it is wise to limit the amount of them in your home.

While most air filters cannot remove odors, carbon filters can. Carbon filters can remove various odors and other gaseous compounds. 

This is because of the adsorption. Other air filters work on mechanical filtering by particle size, which cannot catch small gas molecules.

What Is Not Removed by Carbon Filters?

Although carbon filters are great for removing organic compounds such as VOCs and odors, they do not effectively filter particles. 

This can be a problem for those with allergies, asthma, or other sensitivities since common air particles in the home include mold, dust, pollen, and smoke from the air. 

Girl in a suit coughing due to smoke and girl inhaling an asthma inhaler due to dust and smoke

These particles are let through because they cannot adsorb onto the carbon surface (they are not chemically attracted to activated carbon) and the pores are not sufficient to mechanically filter the particles.

Carbon filters also let water flow through them since water is not attracted to the activated carbon. 

This can be useful, though, since carbon filters can be used to filter VOCs and odorous gases out of water to improve health benefits as well as the taste and smell of the water.

How Effective Are Carbon Air Filters?

Carbon air filters can be an important addition to a household because they take care of pollutants that other air filters do not.

Although carbon air filters are known to be very effective at removing both VOCs and odors, the question of how effective they are at removing each one remains.

VOCs and odors are not the same thing, however, they do overlap a fair amount. 

They are both gaseous pollutants and are similar in size. 

Some VOCs are also odorous and some odors are VOCs. 

Because they are very similar, a carbon air filter’s effectiveness would be about the same for each one. 

Although there is no available information on exactly how effective these filters are, it can be estimated that they are around 95% effective at removing both VOCs and odors since many sources say that they are extremely effective.

Do They Restrict Airflow?

The pores of a carbon filter allow for air to move through the filter without restriction for the most part. 

However, airflow will become restricted when the surface area of the carbon filter begins to fill up with adsorbed pollutants. 

These pollutants can begin to block the flow of air the more they cover up the surface of the carbon filter. 

However, the surface area is likely to be saturated long before this point is reached. So, the air will not be filtered before it cannot pass through the filter. So, you need to replace your carbon air filter before this can happen. 

Where Are Carbon Filters Useful?

To use a carbon air filter effectively, it is important to be strategic about its placement. 

Common sources of odor include pets, bathrooms, and kitchens.

VOCs that end up in the household can come from paint, cleaning products, cigarette smoke, hobbies, etc. VOCs are also even emitted by office equipment such as copiers and printers.

Knowing this, we can deduce where a carbon filter can be at its most useful.

An office would definitely be a great place for a carbon filter to be used. This way, VOCs can be eliminated before they negatively impact the air quality of the office and the rest of the home. 

Office area with sofa and an air purifier that has carbon air filter

Since cleaning supplies can also give off VOCs, a kitchen or bathroom may be a good place to remove VOCs from cleaning supplies. Both of these rooms can also experience odors that the carbon air filter can remove.

A carbon air filter can even aid a bathroom fan in removing odors by being placed in the fan itself. They are also the main mechanism by which ductless bathroom fans function.

While you are painting your home it may also be wise to place a carbon air filter in the room. Ventilating a room while you’re painting is important but a carbon air filter can ensure optimal removal of the VOCs and odors. 

If you struggle with pet odors in your home, it would be wise to put a carbon air filter where your pet spends the most time.

How Often Must Carbon Filters Be Changed?

Unlike common air filters, carbon air filters begin to lose their ability to filter once the surface area begins to fill up with adsorbed pollutants. 

Changing your carbon filter every three months or so should be regular enough to ensure the optimal performance of your carbon filter. But you can always compare this to what the manufacturer says.

Dekiru Carbon Activated Filter Precut for HPA300 Prefilter Compatible with Honeywell Air Purifier Filter Replacement, Fit for Easy Installation Advanced Filters (6 Pack)

Depending on the thickness and quality of your carbon filter as well as how often it’s used, you may have to replace it more or less often.

What Happens if You Don’t Change Them?

You may notice that your carbon air filter starts to smell a few months after it starts being used. 

This is because odorous gases on the surface of the carbon air filter can release a smell as the odors accumulate. 

An odor from your carbon filter is a great sign that you should replace it. 

Other than odors and a noticeable decrease in the effectiveness of the carbon air filter will also occur as the filter ages and begins to fill with VOCs and gaseous compounds on its surface.

Are Carbon Air Filters Toxic?

Toxic byproducts of carbon air filtration have never been found, so it seems that carbon air filters are safe to use in any household. 

The only hazard that may occur is when the filter begins to become saturated with pollutants. VOCs may be released as the filter cannot hold onto them anymore and, as discussed before, VOCs can be harmful to your health. 

This isn’t very common, though, and it can be avoided by regularly replacing your carbon air filter.

Sources

https://www.int-ads-soc.org/what-is-adsorption/#:~:text=The%20process%20of%20adsorption%20involves,that%20phase%20is%20the%20adsorbate.

https://www.epa.gov/indoor-air-quality-iaq/what-are-volatile-organic-compounds-vocs

https://molekule.science/activated-carbon-air-filter/

https://hvactrainingshop.com/activated-carbon-air-filters/

https://www.cdc.gov/niosh/topics/indoorenv/chemicalsodors.html#:~:text=Volatile%20organic%20compounds%20(VOCs)%20are,the%20potential%20to%20release%20VOCs

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