I recently stayed in an apartment that didnt have central air so I created a corsi-rosenthal box since the smoke from the Canadian wildfires were so bad.
After 30 days of continuous use, with very minimal periods of it being turned off, this is what the filters look like!
It's disgusting yet also so satisfying to see the filters get darker from debris, dust, and dirt.
Edit: typos
Those start out white?? I think it's time to replace mine.
Ya, they were brand new filters from the store. I bought them along with the box fan and duct tape.
This apartment doesnt have a HVAC system (just wall mounted AC unit) so it's doing all the air filtration.
This is why I buy my HVAC filters in bulk 4 or 8 at a time and replace them every 3-4 months (less if there is smoke). The difference it makes in keeping the house clean is very noticable. I get very little dust accumulation except in my teens rooms because they leave their doors closed.
I buy these and swap as needed
https://www.homedepot.com/p/HDX-20-in-x-20-in-x-1-in-Standard-Pleated-Furnace-Air-Filter-FPR-5-MERV-8-12-Pack-HDXCP5-012020/332831164