Improving air quality with our new Corsi-Rosenthal Box

This morning, Ottawa has a "Special Air Quality Statement" that says "High levels of air pollution have developed due to smoke from forest fires" and "Wildfire smoke can be harmful to everyone’s health even at low concentrations."

So I am glad that I made a Corsi-Rosenthal Box with five MERV-13 air filters this week!

In case you're thinking of making one, here are some assorted notes:

• There are a ton of videos out there on how to make a box. I started with How to Build a Corsi-Rosenthal Box featuring Dean Richard Corsi from UC Davis (I mean, his name is on the box).
• Dean Corsi uses 2" filters. They are probably better than the 1" filters I used. But I couldn't find any 2" filters locally.
• I got my filters from Home Depot: Filtrete Healthy Living Maximum Allergen Filter MA02DC-3PK-2, 20 in x 20 in x 1 in, 3/Pack 
• The fan came from Home Hardware: HOME ESSENTIALS 20" Box Fan - with 3 Speeds, White. (An inexpensive fan seems to be fine.) [Edit: 2024-08-03 - I've been thinking that it would be nice to have a quieter box fan, so I went online looking for reviews that identified quieter fans. A couple sites recommended the Lasko fan. So I ordered one. It just arrived. And it is at least as loud as the Home Essentials fan, and has a high-pitched squeal that would probably be more annoying]
  
• The inexpensive basic blue tape I had on hand was easiest to work with, but  I ran out and had to switch to heavy-duty black Gorilla tape. Next time, I'm going to have lots of the cheap blue stuff around.
• Corsi demonstrates a 4-filter version that sits on the floor without extra leg supports. That's what I would have done, but I had a fifth filter and a bunch of scrap wood in the basement to make legs so I went with a 5-filter design.
• On TikTok, I saw a guy from California advocating a version that has a single filter taped to a fan. Apparently, this doesn't help much according to a UC Davis case study: Testing different configurations of do-it-yourself portable air cleaners. 
• There are different views on how long the filters are good for. I figure that if the forest fires die out and I only use the box sporadically when people are over, the filters should be good for about a year before I have to get a whole new set.
• Some people say you don't need cowling to block off the corners of the box fan. But Corsi recommends it, so I went with cowling.
• The little piece of wool that shows the fan is on and shows the direction of air flow is not strictly necessary, but I figure it will do until I can get a miniature version of one of those tube man air dancers they put outside car dealerships.