Corsi Rosenthal box
uses a table fan and some air filters
You’ll need a box fan, four air filters (MERV-13 or higher), duct tape, cardboard, and scissors.
fan size & filter size
30cm ~= 12 inch
4 20inch filters https://www.amazon.co.uk/Fixer-Connect-Furnace-20x20x1-Pleated/dp/B0CWYDJ226