With the recent wildfires and the gestures broadly at the world I just wanted to share this link to the Corsi-Rosenthal Box. A simple homemade air filter that can be made with a box fan or several computer fans using off the shelf merv 13 or higher filters from your local store.
Yes, these have existed since before COVID. I had someone elsewhere get made at me because “it shouldn’t be named that! Those two didn’t invent it!” but like, I didn’t choose the name lol. Anyways, I’ve made two for my house (former hoarder house we inherited and we haven’t had the ducts cleaned yet but everything else is clean) and I can say, we both sleep better at night and they worked great through the wild fires.
Anyways, just wanted to share this as a quick little easy project. Or you know, not so quick if you wanna be like the people on Reddit’s r/CRBoxes who 3D print fancy housings and do elaborate computer fan builds. Whichever you prefer.
Edit to add: Someone posted a Build Guide (non Reddit link) on Reddit for making boxes with PC fans.
I know we don’t love Reddit links but
- Here’s a Reddit post for a DIY/buy guide
- An Information post
- A tall computer fan box
- Triangle box fan
- MERV explained by the EPA (not a Reddit link) than you OatScoop
Sorry for the Reddit links, they just have a lot of conversations going on there currently.



I use two thicker filters in a trangle config with just cardboard on the top an bottom. This way my birds don’t stand on the grill and poop in the fan.
Same! With four 120mm PC fans, it works amazingly and actually fits in my room!
I have to assume that this has happened before? Lol. Birds are fun.
so pigeons outside only have wet splat poops because of some sort of microbe, and normally they should poop nugs. but a pigeon laying eggs will hold it in longer and poop out cigars. The smaller birds like cockatiel or budgie will poop out little pellets that cleanly fit between the grills. Sickly old retired bird from the shelter on daily meds will poop out gross slimey puddles. The senegal parrot will attack the robot mop and flip it…
Well that sounds like a lot of… Fun. Lol. But I’m sure that are delightful in other ways.