Some pics matehttps://hydroponic.co.za/hydroponics/acoustic-ducting/
http://www.hydroherbafrica.co.za/product/acoustic-ducting/
I bought 6" (15cm) accoustic ducting from hydroherb and boy has it made a difference. I'm redirecting the hot air out the window now. The ducting is flexible and easy to work with. You can bend the frame slightly to make it square - the 15cm size fits snugly over the outlet fan. This stuff is brilliant. It's not only cooler in the room, it's also quieter. Next to finish my box.