Adjusted the airflow for some 120mm be quiet! fans and made it one part as it fits my heatbed on a prusa printer.

Filter: https://amzn.to/2Te0xQD
Fan: https://amzn.to/36OjNZB

Remixed from demikelo on Thingiverse:
https://www.thingiverse.com/thing:4076795

Update 07.02.2020: Changed the size because filters had a too tight fit and changed the mounting holes because they where too close to the housing. Bad to reach and I went away from using nuts.

Print instructions

No support needed, just place it with the right side on the heatbed...