UPDATE 11/1/2021: my friend ended up getting two Blueair 211+ air purifiers and they've worked marvelously so far! ^_^
I recently did a little bit of research on the best air purifiers of 2020 and I thought I'd share my findings with you folks. :) Blueair 211+ is the #1 air purifier brand on ConsumerReports.org.
At first I went to Amazon and noticed Levoit came in as their Best Seller air purifier. I also noticed IQAir air purifiers were not in stock, aside from their tiny desk models. With all the fires going on these days, I wondered if there was a shortage of IQAir purifiers...?
Many years ago I had researched and settled on IQAir HealthPro as the best air purifier around. It was a bit pricey at $900+ but I did like that it had filter sensors which monitored the filter efficiency. So we only had to buy the filter when it actually needed replacement unlike most air purifiers which usually recommend replacing the filters on a calendar basis, regardless of the condition of the filter.
I then did a google search for "best air filter" and consumerreports.org came up again as #1 sponsored ad and #2 organic search result. I also used them when I had done my research many years ago so I looked into what they said. I got sold again on how they do their testings: https://www.consumerreports.org/air-purifiers/best-air-purifiers-of-the-year/
To test air purifiers, we inject smoke and dust particles into a sealed chamber and measure how well each model removes particles between 0.1 and 1 micron. (Human hair has a diameter of 100 microns.) We use a particle counter to measure the change in particle concentration as the air purifier runs for 15 minutes on the highest speed, and then at a lower speed. And because these run day and night, we measure noise levels, in decibels, at every speed, and calculate annual operating costs for filter replacements and energy use to run the machine 24 hours a day.The three top models in our air purifier ratings earn an Excellent or Very Good rating for particle reduction at a low speed while keeping noise to a minimum. (They all aced the high-speed test, as do many models.) Here’s a closer look at the three best air purifiers we tested, followed by the three worst. They're listed alphabetically.
-This time I noticed consumerreports.org was not available for free any more and required a subscription as low as $10. Found out you can access for free through a library website, which I did, as shown here: https://laflibraryco.com/2020/03/20/access-the-consumer-reports-website-for-free/
-To my surprise, IQAir remained just as expensive as before but it was ranked #10 (score 63) this time around and Levoit LV-H132 came in at #46 (score 21). Ouch. Times have changed! I clicked into the Blueair 605 (rank #1, score 88) and 211 (rank #2, score 85). I've attached CR rankings and 605 and 211 reports.
The Blueair filters are considered "pricey" at around $80 but because it has filter sensors and not just a regular flat time warning light, you still get the most out of the filters anyways which justifies the price. You can also wash the pre-filter, further extending the main filter. :) The Blueair filter at $300 compared to the $900 IQAir, and the Blueair doing a better job at filtering, there's no question, Blueair is the clear winner.
Here's a nice video review by QVCtv of the Blueair 211+ on YouTube: https://www.youtube.com/watch?v=VBuAI4u3W44
At 6m43s It's nice how they show you how quickly it filters smoke in just a few seconds ^_^
There are many models from simple to pro, but the three that stood out were: 211+ (540sqft, $283, $.52/sqft), 411 (161sqft, $120, $.75/sqft) and the 121 (620sqft, $440, $.71/sqft).
Since these run 24/7/365, you could probably get away with just one 211+ downstairs. If you want to be fancy you could have one 211+ downstairs and another one upstairs.
I'll leave the mix and matching up to you. =^.^=