Hi again! Thanks to all of you for your comments. GU-84B need 147CFM and GU-78B need 165CFM airflow. But this is for full power plate dissipation continuous key down. In SSB and CW you can have less. So I'll look for Dayton 2C647, 4C006 and 4C446. I hope the quality of this blowers is good for long time operations. Regards, Mike RL3BM ex. UA6LU