My first filter after approx. 6 weeks.

Gaffers tape holds the filter against the rounded fan face.

The "real" kit: a proper fan and a new filter.

The filter fits this fan perfectly at 11" in diameter.

The scanner after laying on the filter for approx 2 minutes.

The scanner under "normal" conditions.

I became pretty interested in knowing/measuring/improving the air quality in my house after hearing about a group of people in Beijing who are building their own DIY air filters.

The air quality in Beijing is horrific and so these folks set out to measure their air quality and improve it by building a very cost-effective DIY air filter.

They did a fantastic job with documenting their experiments and the results, which allowed me to get started. They only ship to China and Hong Kong, so I set off to build a kit with parts I could buy on amazon.

My own interest in this comes from two concerns:

1. I moved close enough to I-5 that I became curious as to whether this matters.
2. My house is very old, so who knows how much dust is in the air.

To begin, I went out and bought a really crappie Vornado fan for around $30 (from Bed, Bath, & Beyond) and a HEPA filter (from amazon) for around $35. I affixed the filter to the fans face (which was rounded, making it somewhat un-ideal) using gaffers tape [though duct tape would also work], turned the fan on low, and let it run for a approximately six weeks.

Periodically, I'd turn the fan on it's "medium" or "high" speed setting for a bit, but I could smell that burnt electrical smell from electric motors that are about to catch on fire - so it became clear to me that eventually, I'd have to get a proper fan^[1].

I really didn't think anything was happening until one day, I took the filter off and noticed that there was a darkened circular patch where the fan had been blowing air through. (Hooray!). This was small particulate matter that had been removed from the air and captured by the filter.

This inspired me to do two things:

1. Buy a proper fan.
2. Buy a monitor to measure how well (or not well) the thing was working.

I bought a new fan from amazon^[2] and a new filter^[3] and a device to measure airborne particle concentrations^[4]. The fan is "heavy duty" and doesn't appear to have the same "burnt electrical smell" that the other fan had on higher speeds.

I've only been running the fan for a week but already see the dark-ish circle forming. I'm highly optimistic that it's working well and will work for a long time (apparently, you're supposed to change the HEPA filter every 3 months, so your annual filter cost is approx $100).

There are two numbers displayed on the monitor, the left one shows "the count of small particles" and the right number shows "the count of large particles".

What's kind of amazing is what you see when you lay the monitor down on top of the HELP filter with the fan turned on (see the 5th image): the particulate counts go to zero.

What's also amazing is what happens when you cook - in this case, I fried four pieces of bacon without turning on my stove's hood fan. The particle counts jumped up from 500 (small) to 27,000 (small) .. the jump was amazingly high, and so lesson learned: use your stove's venting fan when cooking. The particle counts also jump up when boiling water for tea (though not nearly as high).