I wasn't running any during the winter, but I am now that it's getting warmer here. I'm not sure how much luck you'll have trying to find a high efficiency fan that has good airflow. Usually, you just size it to your needs, how big you want/need it, how much air you need it to move, etc, then find a brand with good reviews. I just ended up getting a 20" Box fan to blow the heat out the window and that is working well for my 3 Neptunes. That's moving a lot of air though, so it's rated at 120W or so on High. That only costs me less than $10 a month to run 24/7 though, so I can definitely live with that.

Is yours moving a good amount of air at 84W?