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G:\Forms & Handouts - 2026\Residential Projects - 2026\8. Domestic Clothes Dryer Vents (Rev 2026).docx Page 1 of 1 Domestic Clothes Dryer Vents – Length Limitations Clothes Dryers The following regulations apply to domestic moisture exhaust ducts in accordance with the 2025 California Mechanical Code, Section 504. • Duct shall terminate on the outside of building and be equipped with back-draft damper • No screens shall be installed at duct termination • Duct shall not be connected by sheet metal screws or other obstructive fasteners • Duct shall not be connected to gas vent connector, gas vent, or chimney and shall only serve clothes dryers • Ducts under positive pressure shall not extend into or through ducts or plenums Domestic Clothes Dryers Where a compartment or space for a domestic clothes dryer is provided, the following restrictions apply: • Minimum 4-inch diameter moisture exhaust duct approved material shall be installed • When a closet is designed for the installation of a clothes dryer, provide a minimum opening of 100 square inches in the door for makeup air or by other approved means • Domestic clothes dryer vents shall be made of metal and have smooth interior surfaces Exception: Listed clothes dryer transition ducts not more than 6-feet in length may be used in connection with domestic dryer exhausts. Length Limitation • Unless otherwise permitted or required by the dryer manufacturer’s installation instructions, and approved by the Building Official, domestic dryer moisture exhaust ducts shall not exceed a total combined horizontal and vertical length of 14-feet, including two 90 degree elbows • Two feet shall be deducted for each 90 degree elbow in excess of two Termination of Environmental Air Ducts • Ducts shall terminate a minimum of 3-feet from property line and 3-feet from openings into the building