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If you have bad odors in your home, you may find that they’re tough to get rid of. Even using the standard filters in an air purifier or your home’s HVAC system doesn’t help much.
If you want to get rid of odors and gaseous compounds from the air in your home, you need to take a different approach. This is where using an activated carbon air filter comes into play.
What is an activated carbon filter?
An activated carbon air filter consists of a bed of carbon encased in a cloth or mesh-like material. These filters remove gaseous compounds from the air. Molecules such as odors and volatile organic compounds (VOCs) are extremely tiny and will slip right through a normal air filter. Activated carbon filters trap these molecules and remove them from the air in your home.
How does an activated carbon filter work?
The activated carbon in carbon air filters is an extremely porous substance. In fact, it is so porous, that typical activated carbon has a surface area of 1000m2 per gram.
Why is the surface area of activated carbon so important? The more surface area that it has, the better chance that the activated carbon will have to capture molecules.
Activated carbon air filters remove gases from the air by trapping them in a lattice of carbon molecules. This process is called adsorption.
Carbon air filters and the adsorption process
As air flows through a carbon filter, all the molecules in the airflow through the filter as well. As the molecules flow through the filter, they pass through the activated carbon. Some of the molecules become trapped in the carbon due to the process of adsorption.
Adsorption happens when a particle gets stuck to the surface of a material. This is an important concept to understand for carbon filters. The more surface area that is available, the better chance that a particle will have to get stuck to the carbon filter.
Adsorption is like absorption, but there is one distinct difference. Adsorption happens when a particle gets stuck to the surface of a material. Absorption happens when a particle gets stuck inside a material.
What to look for when buying a carbon air filter
Not all air filters are made equal. This is especially true for carbon air filters. There are a few different things that you need to look out for when purchasing a carbon air filter:
- Amount of carbon. With carbon air filters, the more carbon that is used, the better. When the carbon becomes saturated with compounds from the air, it loses its effectiveness. An air filter with a thin layer of carbon will only filter out odors for a short period of time.
There are different types of activated carbon as well. Depending on the production process, activated carbon can have more surface area and binding sites, so it will be more efficient. However, generally speaking, the more carbon that is used, the better.
- The thickness of the carbon layer. Carbon air filters with a thick layer of carbon will be more effective than ones with a thin layer. This is because compounds in the air must pass through more layers of carbon. As odors and VOCs flow through a thick carbon filter, there will be more chances for them to get stuck to the carbon material.
- Filter type. Some carbon filters consist of carbon encased in a polymer mesh. These types of air filters are pre-filters. They are not designed to remove normal dust particles from the air, so use them in conjunction with a MERV-rated air filter.
Other types of carbon air filters consist of carbon encased in a standard MERV-rated air filter. If you use this type of air filter, then you won’t need to use an additional filter since the one filter takes care of both standard particle and odor/VOC filtration.
These MERV 11 filters go one step further to reduce odors in your home's air. Perfect for people with pets, or those that are sensitive to certain types of smells.
Pros and cons of using an activated carbon filter
Activated carbon air filters are useful for a few different things. However, there are some drawbacks to using carbon air filters as well.
Here are the pros and cons of using activated carbon air filters:
- VOC filtration. Activated carbon air filters filter out volatile organic compounds (VOCs). VOCs can come from both inside and outside your home. Inside your home, they primarily come from things around the house, such as cleaners, paint, and air fresheners. Smog and air pollution are VOCs that come from outside your home.
- Odor neutralization. Activated carbon air filters also remove odors from the air inside your home. Odorous compounds are too small to be trapped by a standard household air filter. However, many of these compounds will readily react with activated carbon, causing the odor to be removed from the air.
- No particle filtration. Activated carbon filters are not designed to remove common dust, pollen, and air particles found in your home. Therefore, you still need to use your standard MERV-rated air filter in your home’s AC or furnace system.
However, there are some MERV-rated filters that incorporate a layer of activated carbon into their structure. These filters are essentially a 2-in-1 for both odor/VOC and particle removal. If you use one of these carbon filters in your home’s HVAC system, then you won’t need an additional MERV-rated air filter.
- Requires regular replacement. Unlike pleated air filters, activated carbon air filters get less efficient with more use. This means that after a carbon air filter is used for a while, it won’t work anymore.
No matter what, using an old carbon filter will be less effective than a new one. So remember to change your carbon air filter on a regular basis. I recommend changing your carbon filter at least every 3 months. But it depends on the size and thickness of the filter, as well as how many pollutants it removes from your home’s air.
The best thing to do is to check with the manufacturer of the carbon filter that you are using. If you start to smell odors around your home again, it might be time to change the carbon filter.
Cleaning a carbon air filter
Unfortunately, there isn’t a way to effectively clean an activated carbon air filter by yourself. Re-activation of carbon is a complicated, expensive process that is usually done in a factory. So you’re just better off getting a new filter instead.
There are cleaning methods out there that tell you to clean the filter with water or to vacuum the filter. But those methods will only clean out dust particles. It won’t remove odor compounds or VOCs.
Should you use a carbon air filter in your home?
If you have pets, odors, or smoke in your home, then a carbon air filter will help improve the air quality inside your home. Even if you don’t notice any odors, using a carbon air filter can remove harmful VOCs from your home’s air.
Harmful pollutants such as odors and gases will slip right through high-MERV and HEPA filters. Even if you use an efficient pleated air filter in your home, carbon air filters will still provide benefits. Only an activated carbon filter will be able to trap and neutralize odors and gases in your home’s air.
Using a UV light helps to sanitize your room’s air as well. But UV lights are only effective at neutralizing organic and living things. While UV light can destroy mold, mildew, bacteria, and viruses, it won’t help at removing odors or VOCs from the air in your home. Activated carbon air filters are the only way to remove odors and VOCs from your home’s air.
Carbon air filters don’t remove carbon monoxide (CO)
Even though activated carbon air filters can remove some gaseous compounds from the air, they can’t remove them all. Carbon monoxide (CO) will slip right through a carbon air filter. So you’ll still need to use a CO monitor in your home if you use a carbon air filter.
How is activated carbon made?
Activated carbon is created by an activation process that makes it extremely useful for air filtration.
Since activated carbon is so porous, it has many holes and tunnels that drastically increase its surface area. These holes and tunnels act as traps for odors and volatile organic compounds.
There are two main treatments used to produce activated carbon: gas treatment and chemical treatment. These two different methods can produce similar products depending on the steps taken.
Generally, the production of activated carbon follows these steps:
- Carbonization. First, a carbon-rich material is converted into pure carbon by heating it in a chamber. Typical materials used for carbonization are wood, coal, or coconut shells.
The carbon-rich material is placed in a furnace and heated to very high temperatures, around 600-900 degrees celsius. After the heating process, only about 20-30 percent of the material’s original weight remains.
- Activation. During the activation process, oxygen binds to the surface of the carbon in a process called oxidization. Oxidization makes activated carbon very efficient at adsorption, so this is a critical step in the production process.
The carbon is activated in one of two ways:
Gas activation: The carbon is heated while gas is introduced. The introduction of gas exposes the carbon to oxygen which oxidizes the carbon. The carbon is heated to temperatures of around 900-1200 degrees celsius while gas is pumped into the chamber.
Chemical activation: A chemical solution is added to the carbon. Next, the carbon is heated to a slightly lower temperature, around 400-900 degrees celsius.
- Post-treatment. Finally, the carbon undergoes a post-treatment process. This process finalizes the production of the activated carbon. During the post-treatment process, the activated carbon is processed into its final form. It is made into a specific shape and size, depending on what it will be used for.
If the activated carbon is used in air filters, it is made into granular activated carbon. This type of carbon has grains that are about the size of small rocks or sand. This is the appropriate grain size for use in most air filters.
2 thoughts on “Activated Carbon Air Filters – Everything You Need to Know”
A very good article. Thanks.
I have a 3 air filters in our home to try and protect our children from the cigarette smoke coming from the apartment below.
They have an activated carbon pre-filter and hepa filter in each.
From what I understand, it is the activated carbon filter that is best for the smoke.
The GermGuardian purifier is thinner and made of a flimsier carbon prefilter than Honeywell.
Does that make the Honeywell better at getting rid of the smoke or is thickness and flimsiness not factors in determining the amount of carbon in it?
Do you have a recommendation for an activated carbon prefilter that would be best for cigarette smoke?
Activated carbon air filters work best to neutralize odors, HEPA filters filter out the smoke particles themselves. There are a few factors that make one carbon air filter better than another—amount of carbon, total surface area of carbon, thickness of the carbon layer, etc. Most air filter manufacturers don’t report this data so its difficult to compare activated carbon air filters against each other.
Fortunately, the Association of Home Appliance Manufacturers (AHAM) tests various air purifiers. They assign Clean Air Delivery Rate (CADR) scores to each air purifier for tobacco smoke, dust, and pollen. Higher CADR = better.
Here is a link to the AHAM comparison tool: https://www.ahamdir.com/room-air-cleaners/
I find the comparison tool somewhat difficult to use, but they have a link to the directory PDF on the bottom left of the page that has a table of all of the air purifiers. I recommend using the PDF.
Hope this helps,