HEPA & Carbon Filters

What is a HEPA filter?

A HEPA filter is the core of any purifier, it’s what captures the really small particles that are dangerous to our health. The quality of the HEPA filter you use will affect the amount of clean air you’ll get. All HEPA filters have a fixed lifespan, after which you’ll need to replace them with new filters. When they get old their efficiency reduces.  You can read more about different filters on our blog.

How often should I change the HEPA filter?

We recommend replacing your filter after 90 days of use at 8 hours a day at the latest. That’s maximum 720 hours in total. We ship replacement HEPAs starting at Rs.1300 from our store.

Why 90 days? Smart Air co-founder Gus tested a single HEPA on his Original DIY for 200 days to see how long it would last in real Beijing air. After 100 days of use at 8 hours a day in Beijing, effectiveness dropped 4%. After 200 days of testing, Gus’s dirty filter was only removing half the particles in the room. This test was done in Beijing. Indian air and Delhi’s in particular is about twice as bad as Beijing’s so filters won’t last as long in these higher pollution levels.

We know that buying new HEPA filters is a significant recurring cost, so we do our best to keep prices low.

Find out more and see the data on our tests on our HEPA longevity test blog post.

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.

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.

Can I wash my HEPA filter?

We tested this in our labs, we tried washing, vacuuming and scrubbing a HEPA filter to find out if there was a cheaper way of making your filter last longer. Turns out none of these methods were effective in increasing the lifespan of a HEPA filter, so we still recommend replacing them when their time is up.

Smart Air low cost purifiers

Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.

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