With the wildfires in Canada, Minnesota, and expectation that there will be more from elsewhere in the next couple of months. you may be looking for help in setting up air filters. The Corsi-Rosenthal Box Fan filter is a solution that may be what you're looking for. The recommendation is to use MERV 13 filter Higher values don't offer significantly more help with relation to smoke, but if you are unable to get the MERV 13 filters, MERV 12 and 11 filters will provide some filtering.

I print these at the thickest layer height as that gives the best time options for this item, and we're not aiming to make a piece of art. That said, I'm getting between 1 and 2 hours for one of these on my printers. The A1 takes nearly 2 hours to print just one as that is all that will fit on the plate. 1 on a P1S takes about an hour and a half. Something like an hour and 24 minutes. however when I set it up with 2 the pair print in about 2 hours ans 12 min. On a FlashForge AD5X I am able to put 2 on the build plate, and on that device I'm getting 2 in 2 hours.

Recommendations, Use Mouse Ears or Dog ears, (seems like that might be the option in Europe) This is preferable to a brim, as the brim will add a significant amount of time to the print job. Again, it's not art, thickets layer height will mean fewer layers in the print. You need 8 of these in total so plan accordingly. Having multiple printers working on this at one time means less wait time.

Once printed the recommended filter size for this model is imperial 20" x 20"x 1" Each corner gets taped, in any pattern that works well for you. I suggest laying all filters in a row with pleats oriented the same way. Tape the top surfaces along the top surface of the edge. Once all 4 filters are taped in a line, stand the filters on edge and fold each filter over the seam and tape the edge of the filter to provide a souble angle taped seal between the two.

Once you have the first 3 seams taped together, set out 4 of the 'corners' to be on the floor, and set the filters in the grooves in the corners. You can use the holes in the flat of the corner to link across the square. Now tape the remaining corner. Add top corners to help stabilize the structure, and provide a bit of a surface for the fan to rest upon.. The fan should be modified to provide protection from having air brought into the box through the corners of the fan. I'm unsure of how important this is, however I think it may give a better indication of whether filters need to be replaced.

A set of 4 20x20x1 merv 13 filters are widely available and if there isn't a rush on them, or a shortage of them, should be available as a set for under $50 (As of the middle of 2026, s with everything else these days, it's subject to change.) Box fans duct tape will most likely be under $30. And usually the box fan will be in a box that can provide the material to modify the fan to not pull back through the corners. All told, you're looking at a high volume high quality air filter for well under the price of a residential stand alone air filter.

Note that these corner pieces are mostly superfluous. They can help with stability, but the tape is doing the majority of the work, and it can be stable on it's own. I saw a question about whether anyone could do this for 3d printing. The answer is yes people can. The print time though suggests that this is probably not the best use of time. Others may think of it differently. I like the thought that it will provide stability, but I think that for more stability there will need to be more vertical support. I've pointed out that folding corrugated plastic, and even corrugated cardboard can be used to provide the bracing. Some of those solutions can be used her too. Another option would be to make a wooden frame that allows the user to slide all 4 filters out and replace them. Is it the best option? Kind of depends on your idea of what is 'best."

The model may be changed to support any variation you need. If you need smaller than these to fit on a smaller build plate, that's perfectly OK. If you want to decorate it, ad voides to improve printing speed, that's entirely OK.