What is a required characteristic of duct construction for grease ducts?

A required characteristic of duct construction for grease ducts is that they must be coated. Grease ducts are used in commercial kitchen settings to carry exhaust from range hoods, and they can accumulate grease over time. Coating the interior of the duct with a suitable material helps to prevent the buildup of grease, which can pose a significant fire hazard. Additionally, a coated surface is easier to clean, thereby maintaining proper ventilation efficiency and safety.

While other characteristics such as insulation or specific materials like aluminum may be beneficial in various situations, they are not strictly mandated by code for grease ducts. The emphasis on coating reflects the need for improved safety measures and maintenance practices in environments where grease accumulation is a substantial concern. This requirement ensures both compliance with safety codes and the efficient operation of the grease exhaust system.