You need to keep good airflow around the cards. The more airflow, the better. I place a box fan directly in front of the cards so that it pushes the hot air from the the rig away from the cards and also blows air through the cards. This lowers the temps so you don't need to run the fans on the card too high. If you have 1-2 rigs that may be enough depending on the size of the room and if you have good ventilation. Any more than that, you likely need to look for a way to exhaust the hot air away so that it can be replaced with cooler air and you're not just circulating the same hot air around the cards. Angry Chicken on Youtube posted a video with a creative solution he's going to try using a well ventilated box.
https://www.youtube.com/watch?v=Vu-ryc4Wx14
yes, the most important thing is cool and fresh air. https://www.youtube.com/watch?v=Vu-ryc4Wx14
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