The Big Ass Fans Powerfoil X4 is engineered to improve indoor air quality and occupant comfort. Purpose built to provide maximum airflow in even the toughest conditions, the Powerfoil X4 raises the bar on comfort, safety, and quality for industrial fans. It features a full-fan IP56 rating for use in harsh environments, a redesigned airfoil system, and diameter options ranging from 12' to 30'.