Clothes Dryer Venting

Crushed and blocked clothes dryer ducting can result in a home fire.

California Real Estate Inspectors recommend home owners carefully check the exhaust ducting serving their automatic clothes dryers. Crushed or obstructed dryer ducts have resulted in home fires causing great structural damage, personal injury and even death. Without adequate release and dispersion to the exterior overheated lint trapped within the ducting may catch fire or at the very least cause much longer drying cycles thereby raising the cost of electrical or gas consumption for the home owner.

Because many ducts pass through combustible wall framing and through the foundation crawl space it is imperative that during normal home owner maintenance these duct be checked. Ducts terminating within foundation crawl spaces can also be problematic due to pumping warm moist air into areas ripe for the cultivation of mold and encouragement of wood boring pests.

Here is what the California Mechanical Code requires regarding clothes dryer exhaust ducting:

504.3  Clothes Dryers
504.3.1  Moisture Exhaust Ducts. Moisture exhaust ducts shall terminate on the outside of the building and shall be equipped with a back-draft damper. Screens shall not be installed at the duct termination. Ducts for exhausting clothes dryers shall not be connected or installed with sheet metal screws or other fasteners which will obstruct the flow. Clothes dryer moisture-exhaust ducts shall not be connected to a gas vent connector, gas vent or chimney. Clothes dryer moisture exhaust ducts shall not extend into or through ducts or plenums.
504.3.2  Domestic Clothes Dryers. When a compartment or space for domestic clothes dryer is provided, a minimum four (4) inch diameter moisture exhaust duct of approved material shall be installed in accordance with this section and Section 504.0.
When a closet is designed for the installation of a clothes dryer, a minimum opening of 100 square inches for makeup air shall be provided in the door or by other approved means.
504.3.2.1  Domestic Dryer Vents. Domestic clothes dryer moisture exhaust ducts shall be of metal and shall have smooth interior surfaces.
Exception: Approved flexible duct connectors not more than six (6) feet in length may be used in connection with domestic dryer exhausts.
Flexible duct connectors shall not be concealed within construction.
504.3.2.2 Length Limitation. Unless otherwise permitted or required by the dryer manufacturer’s installation instructions and approved by the Administrative Authority, domestic dryer moisture exhaust ducts shall not exceed a total combined horizontal and vertical length of fourteen (14) feet, including two (2) ninety degree (90°) elbows. Two (2) feet  shall be deducted for each ninety degree (90°) elbow in excess of two.

President, Jabuka Home Inspections
https://jabukahomeinspections.com/