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4 Inch Vent Cover: What Size Does a Range Hood Need? 2026

A 4 inch vent cover is the correct cap for a dryer, bathroom fan, or small wall vent — but it is undersized for most range hoods, which need at least a 6-inch duct under U.S. code. This guide explains what a 4-inch vent cover fits, the duct size a range hood actually needs by CFM, and what to do when a 4-inch opening is all your kitchen has.