DIY Air filter

For those who did not order an air filter, or want to try to roll out your own, there is a nice post on hackaday for some ideas:

The direct link is below:


Anyone tempted by this should be aware you’ll still need to rig a hepa filter to it to get the smallest particulate. There’s a good discussion about its strengths and pitfalls in the comments.


HEPA is just a containment system for particles, which uses a number of methods to capture the particles. That’s why HEPA filters invariably are made with pleats, because particles flowing through the filter have additional surface area that catches and contains the particles of smoke, gas, etc. through interception, impact, and diffusion. In general, the tighter the pleats, the better the HEPA efficiency is. Also, the dirtier the filter the more efficient it is (as long as it still allows airflow) because that decreases the brownian motion of the particles flowing through the filter and increases the chances of it getting caught.

Other interesting bookmarks:

…and results of someone stuffing a furnace filter in front of a box fan, tested using a particle counter:


Yes, I know how HEPA works, and a ton of DIY air filters can’t be considered to filter particulate matter without them. I said HEPA, but I’d accept even a furnace filter attached; a lot of the discussion so far doesn’t include even that much.

I built one of those box filter fans, and they’re…not very good. I’ve seen the same meter counts videos, and one thing they don’t mention is that there’s just not a lot of airflow coming through those filters. Certainly nothing even close to what comes out of a pre-built air filter.

I’ve gotten better results by using a very deep filter, which is obviously less restrictive, but it’s still not what I’d call “good.”

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Marius Hornberger recently updated his dust filter and showed how he made his own pleats for large particulates and also used bought filters. Matthias Wandel also has a few videos. Adding the fumes carbon filter is one more step. I’d like to have something for the occasional indoor demo but For now I’ll do the window. Here at filter build.