The CIX3Z factory-built zero-clearance grease duct for restaurant and food-service-related construction provides superior airflow performance, reduced grease buildup, easier maintenance and access, and lower installed costs compared with site-built rectangular duct. It is tested and listed to UL 1978, Standard for Grease Ducts, and UL 2221, Standard for Tests of Fire Resistive Grease Duct Enclosure Assemblies.