This thing allows you to boost the airflow from a standard 18-inch wide forced air ventilation register. It uses a standard 120x120 mm muffin fan and easily attaches to the vent using magnets.

The parts are in two pieces that are glued together in the middle. The magnets are 1/2" diameter rare earth disc magnets. I have found the IPS Acrylic solvent Cement #16 to be excellent for welding all types of 3D printing filaments including PLA, PETG and ABS. The fan is held in place using #4 screws.

magnets: https://www.kjmagnetics.com/proddetail.asp?prod=D8H2

I only use these with air conditioning, so remove them in the winter.