A box fan and two furnace filters taped into a triangular air cleaner.
FiltAirs DIY Air Filter by Open-Source-Imports
https://thediyjunky.com/@open-source-imports/filtairs-diy-air-filter
Licence: CC-BY-SA-4.0
Adapted from: https://www.appropedia.org/535_FiltAirs_DIY_air_filter
Original author: Bikash Pradhan, Nicole Salas, Amin Younes
Original licence: CC-BY-SA-4.0

A low-cost air filtration unit built from a box fan, two filters and cardboard, assembled with duct tape.
| Part | Size / spec | Qty | Unit cost |
|---|
Required total: $0.00
Place the unit face down with the inlet side up.

Place one filter on the unit and align it with the edge of the box fan, and verify that the arrow on the filter points towards the fan.

Sit the unit up and pull both filters out to form a triangle, and secure the point of the triangle.

Using the box that the box fan came in, or other cardboard with at least 20x20 inch dimensions, cut out two triangles.

Place one triangle on top of the filters, making sure the cardboard slightly overlaps onto the filters.

Gently fold the edges of cardboard to sit flush against the box fan and secure with duct tape.

Flip the unit over so the bottom of the fan is facing up, and attach the other triangle to the bottom.

Lay the unit down with the box fan on the ground and the point of the triangle facing up, and seal the remaining edges.

The unit is assembled and ready to be used. Place the unit sitting upright in an open area.