Depends if you want to build your own or not [1]. If not, I think purpleair is the way to go (I use the same sensor as them but they have two I believe for redundancy). As for air purifier, I highly recommend Blueair. They’re expensive but was the only purifier I had that managed to pull the PM2.5 indoors to near 0 during this terrible wildfire season in California.
A bit off tangent, but Blueair purifiers was the only brand where the output air was 0 PPM2.5 during wildfire season in the Bay Area (I have the $50 uncalibrated laser PPM sensor that purpleair uses so interpret this as you want). I tried Dyson, Winix, and making a V-shape DIY purifier with a vornado fan. Nothing was able to pull the indoor air below 15 besides Blueair so I recommend it to any of my family and friends.
I have a bunch of air filters (I live in the bay area during fire season).
Coway Air Mega
Coway Mighty
Blue Air
Medify Air
They're basically all equivalent and they all work.
The reason I like the Medifyair is because it can move the largest volume of air relative to those so it can clear a space quickly (and quietly). I also think it looks nice (though it is huge).
Of the rest, the Blue Air uses weird custom filters which I think cost a little more (though I haven't had to replace them yet). The Coway Mighty is also pretty small and mostly for a tiny room.
Relatedly, if you're interested in sensors I think the TemTop sensors are the best (I've tried a bunch of different ones, and a lot of them suck).
There was a thread on HN around a week ago around just this topic. Well worth reading through it "Build a do-it-yourself home air purifier for about $25" for the comments on filters and sensors. [1].
They are expensive, and it doesn't have a built in sensor, but I have an IQAir healthpro compact and have confirmed with my own particle detector that it filters out > 99% of PM0.1 particles, and 100% of PM2.5 particles.
If you don't care what it looks like, you can easily build your own air purifier for much cheaper. All it is is a blower fan which forces air through 2 or 3 filters, with the last being a HEPA filter. You can get all the requisite pieces for about $100.
You might conclude that the only real option is to buy a positive pressure fresh air system, but this comparison doesn't match my experience. I have no trouble driving the PM2.5 very close to 0 with a few standalone purifiers in my house (verified with a couple air quality monitors) even during bad wildfire smoke events. I'll grant I live in a modern house which is pretty well sealed, but it's also a question of sizing the purifier to the room's size and drafts.
There are some orthogonal advantages and disadvantages though. On the upside, you'll reduce CO2 and other pollutants from inside your house -- it can get quite stuffy when you can't ventilate due to poor outdoor air quality. A downside is that it may also bring in air at a different temperature or humidity than you'd like (though that can also be controlled to some extent with a HRV/ERV.)
You seem to have relatively clean air already. I probably wouldn't even bother with air purifiers in such a situation.
Where did you buy air filters? I live in a third-world country and couldn't find them anywhere, so I had to buy a factory-built purifier. It really struggles to keep up when it's 1000+ µg/m³ outside. I'd like to add a second one (preferably DIY).
If you’re looking for an air purifier, the Honeywell HPA300 ($200) is more than enough four our three bedroom house (despite the 465sq ft rating).
I want to be able to recommend the Bissell Air400, as it is quieter, has a built in PM 2.5 meter, auto adjusts to pollutants, and the filter works at least as well.
Unfortunately, it randomly turns itself off. This seems to be a design flaw, as many other people report the same thing. Also, it doesn’t seem to use a PID control loop to set fan speed, so the automatic speed controller sets itself far too low for our house. On the bright side, it is frequently on sale for 50%+ off, since it has a terrible reputation.
In practice, I leave the honeywell on, and use the bissell if there’s a problem (cooking smoke, allergies, wildfires, etc). In tandem, the two are able to lower PM 2.5 by over 90%, which is more than enough for fire season.
Edit: In hindsight, I would have bought the HPA 300, and a standalone sensor like the ones from purple air.
Yeah, same thought. Something like the Coway air filter ( https://www.youtube.com/watch?v=zxiDrEnjYEo ) regularly sells for under $200, and it is going to be much quieter than this option. It also has been tested fairly extensively from what I've seen, it's EnergyStar approved, etc, and it has a built in sensor. It doesn't look too bad either.
But I understand the point, especially in times when you can't find a purifier.
Several people have recommend you air purifiers. I would add one thing, look at the price of replacement filters. Air filters are similar to printers in a way. You become tied to a company and have to buy replacement pieces every year or so. Some have bad track record (quick device depreciation because of out of stock filters, etc.)
I don't mean to go against the spirit of the thread but does anyone know how these DIY compare to actual commercial products - and can anyone recommend a good air purifier? Thank you
Speaking of air purifiers, does anyone have recommendations for one that is quiet and still effective?
I have a pair of Electrolux EAP300s, in small rooms.
Unfortunately on the lowest manual setting ("Quiet") they hardly do anything for air quality. And they're still louder than I like. I think they really optimized for cost; these devices feel very light and plasticy, the fan sounds cheap and has an uneven tone to it, and its speed keeps oscillating back and forth. The purifier itself is also not stable and it can make an annoying noise if placed on a surface that ends up vibrating along.
I also thought about DIYing one with noctua fans (which I know are quiet, and I have plenty of them in my PCs), but I suspect they're not going to be very effective.
[1] https://www.powu3.com/airquality/
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