I currently have two air to air Nova Cool units mounted under the Nav station seat. There are two vents at 90*, one is roughly 4x10 inches, the other is about 5x5. Both have screens.
I will be adding a 140mm Noctua (muffin, or computer type) fan, with its own new vent hole, wired with potentiometer to reduce the 2000 rpm
speed (and 31db noise).
So the question for you engineers out there is should the fan blow hot air out of the vent, or into it?