Fan filter frame

I live in the Pacific Northwest, USA. During summer, we are subject to poor air quality due to wildfires (exacerbated by climate change). One of the cheapest & most effective mitigation techniques for this is to attach a smoke-filtering element to a box fan, and place these throughout the house. In the past I've attached filters to the box fans using masking tape, but it makes a mess, is hard to switch, and destroys the filter when I need to box up the fan at the end of smoke season. I've seen a few different filter mounting systems here & other places online, but none fit my fans properly.

These filters brackets are designed to allow attaching a standard 20x20x1 air filter to a Utilitech 20" box fan (available exclusively at Lowe's). In addition to the brackets, 3x M3x8 screws are required to attach the brackets to the fan (sorry I couldn't get a pinch mount to work reliably).

Steps for installation:

1. Print out the set, including 1 bottom frame and 2 side frames (the 3MF includes the set). I recommend printing in PETG or ABS for durability/flexibility - PLA will be too brittle to hold up.
2. Apply a piece of electrical tape to the bottom of the fan, to close the small gap that aligns with the cable.
3. Attach the bottom frame over the base screw, the extrusion on the front will fit into a gap in the grille. Mark and drill a hole for the M3x8 screw. Insert the screw, threading into the plastic. Be careful not to overtighten.
   
   Attach one of the side frames, the extrusion on the front will fit into a gap in the grille about 2¾" down from the seam at the bottom of the top corner. Drill & screw, then repeat on the other side.

I printed with a 0.6mm nozzle, 0.35mm SPEED layers, in Prusament black PETG. Happy breathing ;-)

[TinkerCAD Project]