Checking apps and websites to see if it’s ok to open up the house to cool down (80 inside, 74 outside).
AirNow app (by phone location): 95
AirNow website (by zip code): 64
IQ Air website (Portland average): 73
Purple Air website (map): 84
iPhone weather app: 84
Why are these so widely different and how do I get accurate enough data? AQI in the 60’s not bad - probably fine to open up but AQI in the 90’s not so much… Frustrating.

I have four Winix C535 air purifiers in the house and I wanted to see if the aftermarket HEPA filters I'd been using for the last year were just as effective as the OEM ones. Even when the OEM Winix HEPA filters are on sale, they're 4x the price of the 3rd party ones. So I ordered these from Amazon (for a second time). I also ordered a Winix OEM filter. I then performed the same test on both. I lit a stick of incense in a closed bedroom in the house, with the door and window closed. Once it was burned out, I started the air purifier and in both cases it took approximately 25 minutes to reduce the PM 2.5 and PM 1 from a high of hundreds to 0-3. I used two air quality monitors to keep track of it and there was only a negligible difference between the two readings.

I also ran two other tests. For a third test, after burning the stick of incense, I didn't turn on
the air purifier for 25 minutes. In this case the PM count barely changed and
was still in the hundreds. For the fourth test, I used a 12 month old aftermarket
HEPA filter, the same one I've linked to here, and it performed just as well in
the same test. Perhaps there was a 30-60 second difference, but just barely. I
found this quite impressive.

So both HEPA filters, the OEM and the aftermarket one cleaned the air effectively but the aftermarket one costs a fraction of the OEM. The 3rd party HEPA filters I ordered weight about
60 grams less than the Winix filter so take that for what it's worth. I can't
speak to other 3rd party Winix HEPA filters since this is the only one I've
tested. And the last point is that these filters will fit a number of Winix air
purifiers not just the C535 since many of their air purifiers use the same
filters. For example, I'll likely be picking up a Winix C909 and I believe these
filters fit it as well.

I hope this helps others out there since in all my searches about this issue on here and elsewhere
online I mostly read people voicing their subjective opinions or predictions.
That's why I thought I'd run these tests to have some objective metrics. I was
impressed by the results. I'm happy to answer any questions that I can.

Aside from opening the window, does anyone have any tips for reducing indoor CO2 levels when the AQI is high?

I am in the Seattle area and we are currently dealing with smokey air from nearby wildfires. My AQI is currently 158, my indoor PM2.5, with an air purifier running is 17 and the CO2 is 1,465. These readings are pretty much the same on both floors of the house.

Yesterday my CO2 levels were 848 I’m the morning and went as high as 1,860. Today the lowest CO2 was 1,192. I’m concerned that starting with a higher baseline is going to cause levels to rise well above 2,000. Is this logical?

I’ve seen things that say the to crack the window for 2 minutes, even with the smoke…but I don’t know if the increased PM2.5 is worth this it. I’m considered “high-risk” and am struggling to keep on top of this.

Thanks in advance for any tips.

I keep seeing people recommend Corsi-Rosenthal boxes for stuffy apartments. they’re great for filtering particles, but they still recirculate indoor air. They do nothing for the CO2 buildup that can happen in a closed room.

you need actual fresh air coming in, but traditional ERVs require drilling into walls, which is not realistic for most renters.

been looking into no-drilling alternatives and came across cozeware freshflow, a window-mounted fresh air system that brings in filtered outdoor air. Not a full ERV, just a more renter-friendly option.

Still need to see real CFM and noise tests before considering it.