granular carbon

How Does a Carbon Air Filter Work?

Some friends of mine recently built a new home and just moved in. The house is beautiful, but with all the new construction, cleaning, and painting going on, they found themselves overwhelmed by all the smells in the house. It’s too cold to open the windows and let the place air out, so I gave them a carbon air filter to help reduce the odors filling their new home. After about a week, the smells were gone, and they were much happier (and no more headaches from the smells!). When they asked me how the carbon air filter worked, I realized just how interesting the technology is.

Activated Carbon

The key to a carbon air filter is the activated carbon layer on the surface of the filter. We’ve talked before about how air filters work, but the layer of carbon adds an additional element to filtration process.Extruded carbon

Making activated carbon is a two-step process. First, the source material (nutshells, coconut husk, peat, wood, or coal) is carbonized – that is, heated to around 600 Celsius in an environment absent oxygen, so it can’t burn – and then activated. Carbon is activated by exposing it to an oxidizing agent – such as oxygen, steam, or carbon dioxide – in a superheated environment (again, around 600 Celsius), which opens up pores on the surface of the carbon, greatly increasing the surface area. Additionally, this process gives the carbon a positive charge, which attracts particles that pass through the filter and binds it magnetically to the surface.

As air passes through the carbon filter, the regular filter media captures dirt, dust, animal dander, and other particles as the air passes through the filter. The carbon, with its microscopic pores and its positive charge, binds with gasses and odors that are in the air. This is a chemical process known as adsorption. In the case of my friends, paint fumes and construction dust and dirt still in the air.

Just like a regular air filter, over time, the nooks and crannies of the carbon particles get filled with gasses and other particulates, and the filter will need to be replaced. Usually, a good carbon filter will last for three months, but if you live in a home with exceptionally strong odors, or a lot of dust and dirt – just like my friends – you may need to replace it more often. But with a carbon air filter in your home, you’ll breathe easier.


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