Depending on a number of factors, your ventilation, as planned, should be adequate. :thumbsup:

The length of the filter is not real critical, and you have a good general size in mind. Make it easy on yourself and buy screen that is 30-40cm then make the filter as long as the screen. When covering the screen with the stocking, it tends to get caught on any cut ends sticking out, so the fewer cuts you make the easier it is to build the filter.

PC :smokin: