DIY Carbon Filter

What is activated carbon?

HEPA filters are designed to capture particles like the small PM 2.5 particles. Activated carbon, though, captures odors and gases like volatile organic compounds (VOCs). VOC is a big category and includes harmful carcinogens like formaldehyde and benzene.

Does activated carbon really work?

To answer this question, we ran tests with an Industrial Scientific MX6 iBrid gas detector that can detect VOCs and a host of harmful gases. In an enclosed 4.14m2 porch, we lit three cigarettes (known to emit formaldehyde and benzene), turned on a Cannon fan with a carbon filter, and tracked VOC concentration. We also ran a control test of a fan with no carbon attached. The results (left) showed the carbon layer effectively reduced VOC concentrations.

Does everyone need a carbon filter?

Not necessarily. Not all homes have dangerous levels of harmful gases or VOCs that would call for a carbon filter. VOCs are more common in homes:

• with recent home renovation or repainting
• with smoke or other offensive odors
• near a source of gas pollution like a factory

If you have inflammation or asthma symptoms, you may also consider using a carbon filter.

Purifier companies have a financial incentive to convince people to buy carbon filters. They make more money if they can scare people into buying carbon. We won’t do that. Check the facts and data first before spending your money.

Do I still need a HEPA and a Carbon?

Yes. Activated carbon is not very effective at filtering particulate pollution, the primary pollutant affecting cities in China. For that, a HEPA is still the best choice.

How do I install a carbon filter?

If you use a Cannon, you can install an activated carbon filter and a HEPA filter simultaneously. On the fan opening, first place the HEPA then place the carbon filter on top (as shown in the Filter Order diagram to the right).

Please note: the carbon filter shouldn’t be used along with a HEPA on the Original as the air flow rate is not sufficient. It is possible to use just a Carbon filter on the Original (no HEPA filter) if you think you have a serious VOC problem.