Thread by @rover_18

I built a makeshift air purifier with an HVAC filter & fan. It’s making a big difference, reducing smoke smell & irritation. I’m measuring 50% reduction in particulates after 30 mins, reducing indoor AQI from “very unhealthy” classification to “unhealthy for sensitive groups”.

Running ~1hr on/off cycles to compare air quality with/without. Just started 2nd on cycle. I’ll post legit plots later & a writeup on @hackaday.io, but for now, here’s a screenshot of my live preview, showing 2.5um particle counts in ug/m3, with ~50% dip during first on-period.

Didn’t know someone else had already approached this quantitatively, with amazing results:

https://twitter.com/huffmanlabdu/status/1303851720645079042?s=21

Here’s a simpler design.. a 20x20” filter taped directly to a 20” box fan. Use what you got. For better efficiency you want to seal the filter against the outflow side of the fan.

https://twitter.com/edtufexis/status/1304872224470564866?s=21

https://t.co/MN9iyRY4hO

Stalled just a hair short of 50% reduction this cycle.

I’m using a MERV-11 rated filter which, turns out, only promises 65% reduction for particles smaller than 3 um. Should get 90% or better with a MERV-15+ filter. Off to the hardware store..
epa.gov/indoor-air-qua…

My wife just brought up the issue of storability after the smoke clears. To which I say 🤷‍♂️

Outdoor AQI spiked absurdly high this morning, corresponding to the #BobcatFire 4am flare-up in Monrovia Canyon. My filtration experiment was helped by generally improving AQI outside, but there is a clear correlation with filtration on vs off. Need a better filter (MERV-15+)..