What must be the minimum clearance for a grease duct to noncombustible construction?

The minimum clearance for a grease duct to noncombustible construction is established to ensure safety and prevent the risk of fire. A clearance of 3 inches is necessary to allow for proper ventilation and to accommodate any thermal expansion of the duct. This distance helps to minimize the transfer of heat from the duct to nearby materials, reducing the likelihood of ignition, especially given that grease ducts can reach high temperatures during cooking processes. Proper installation and maintenance following this clearance requirement are crucial for compliance with safety standards in kitchen and food service environments.