Dryer Vent Cleaning & Water Heater Flush - San Mateo

## What We Found: Multiple Code Violations in the Dryer Exhaust System During a residential dryer exhaust cleaning and inspection at a San Mateo home, our technicians identified three significant issues with the existing exhaust system. First, the transition duct was semi-rigid metal but was concealed within the building's construction, which is a direct violation of IRC M1502.4.3. Concealing semi-rigid duct inside walls or floors prevents access for cleaning and inspection, and the material is prone to moisture absorption and cracking over time, which accelerates lint accumulation and restricts airflow. Second, the duct path included a reduction from a standard 4-inch diameter down to a 2-inch section before returning to 4 inches. This type of restriction creates a severe choke point in the exhaust system. IRC M1502.4.1 requires a minimum 4-inch diameter throughout the entire duct run. A 2-inch section effectively cuts the cross-sectional airflow area by more than 75%, causing back-pressure that forces lint to settle inside the duct and significantly increases the risk of overheating. Third, one section of the duct was found to be completely disconnected and unreachable, meaning moist, lint-laden exhaust air was venting directly into the building cavity rather than to the exterior. This is a violation of IRC M1502.2, which requires the exhaust system to convey all moisture safely to the outdoors. A disconnected duct in a concealed space can lead to mold growth, structural moisture damage, and in the case of a gas dryer, a potential carbon monoxide concern. ## Dryer Exhaust Cleaning and Water Heater Flush Performed The technician performed a thorough residential dryer exhaust cleaning and inspection, clearing lint accumulation from the accessible portions of the duct system using rotary brush and extraction methods. The full extent of the cleaning was limited by the concealed and disconnected duct sections, and the homeowner was advised that a duct repair and reroute (Dryer Duct Installation and Repair) would be required to bring the system into full compliance and restore safe, efficient exhaust. A residential dryer exhaust inspection was also completed to document all findings and establish a baseline for the remediation work ahead. In addition to the dryer vent services, a standard water heater flush was performed. The tank was drained and power-flushed with fresh water to remove sediment buildup from the bottom of the tank. After the flush was complete, the drain valve was closed, the tank was refilled, and the pilot light and burner were confirmed to be operating correctly. Hot water was expected to be fully restored within approximately one hour of service completion. Regular annual flushing, as supported by IPC Section 501 maintenance access requirements, helps extend tank life and maintain heating efficiency.