This is an example of less is more. The 10" 4 blade fan (30) is quite superior to the noisy 12" 10 blade fan, (#19) The 12" was advertised as flowing considerably more air than the 10" fan. Our airflow results indicate the advertised flow rates do not correlate with actual flow rates experienced in a Tiger. Fans with 6 or less blades are more efficient in the Tiger application.