We are getting a lot of bad air because of the wildfire smoke near us. Our PM2.5 is regularly above 250 µg/m3 outside (!) and it was climbing up over 80 inside. We had a cheap paper filter in our HVACs, and wanted to upgrade, but apparently everybody else had the same idea because the best we could find at the local store was MERV-11, which isn’t good enough to filter the smoke. You need MERV-13 or better to get the PM2.5 particles in the wildfire smoke.
We use an IQAir monitor that we got as a gift, which shows the outdoor and indoor quality and has worked OK for us, but as many commentators pointed out, there are better cheaper models that do the same or more, like this multifunction tester that measures the PM2.5 and CO2 of the IQAir, plus formaldehyde (HCHO), volatile compounds (TVOC) and PM10. It’s also faster, our IQAir takes 10 minutes to react to changes.
While they didn’t have smoke filters, they did have this stuff called “Filter Charger,” so we got some. It’s kind of like hair spray that you put on the filter and it bumps it up a couple of MERVs. It also leaves a nice lemon citrus smell.
We tried it on our paper filters and over 30 minutes, our indoor air measurement went down from slightly over 80 to a little over 50. (the numbers are vague because of limitations in the measurements, our measurements are likely accurate to ±10 µg/m3 so I grossly round them.)
With our MERV-11 filters we stayed in the 50s at the end of our 30 minute test. After we added the filter charger, our PM2.5 dropped to ~25 and our air was noticeably fresher.
It has only been a couple of days, but our PM2.5 has stayed in the 20 to 40 range, with journeys into the 40s correlated to things like opening the door or stirring up things a lot with things like vacuuming.