Dryer Vent Cleaning & Duct Repair in Pacifica, CA

## What We Found During a routine dryer vent inspection at a residential property in Pacifica, our technicians uncovered three serious issues that were degrading airflow and creating significant fire and carbon monoxide hazards. First, the exterior termination cap was wedged permanently open by a packed mass of wet, compacted lint lodged in the corners of the flap. This rendered the backdraft damper completely non-functional, violating IRC M1502.3, which requires the termination to be equipped with an operating backdraft damper that closes when the dryer is not running. A stuck-open termination also allows pests, moisture, and cold air to enter the duct system freely. Second, the semi-rigid transition duct installed by a third-party appliance installation crew was substantially oversized for the available space. Per IRC M1502.4.3, transition ducts connecting the dryer to the rigid exhaust system must not exceed 8 feet in length. The oversized duct had been compressed and coiled to fit the space, creating sharp bends and significant airflow restriction. Restricted airflow causes lint to settle inside the duct rather than exhaust to the outside, raising fire risk and forcing the dryer motor to work harder over every cycle. Third, and most urgently, a booster fan was discovered installed in the garage section of the duct run. The fan had been disconnected from its electrical supply at some point, meaning it was no longer spinning and was acting as a solid blockage in the middle of the exhaust path. Even if it had been wired correctly, its installation would still be a code violation. IRC M1502.4.5 explicitly prohibits domestic booster fans in dryer exhaust systems. Standard inline duct fans are not rated for lint-laden, high-temperature exhaust air and present a serious fire hazard. For a gas dryer, a blocked or leaking duct also introduces a carbon monoxide risk. Only a UL 705-listed dryer exhaust duct power ventilator, installed per IRC M1502.4.4, is permitted if a powered assist is genuinely required. ## What We Did Our technicians performed a full dryer vent cleaning and inspection, removing the compacted lint from the termination cap and restoring the backdraft damper flap to proper operation. The oversized semi-rigid transition duct was removed and replaced with a correctly sized, UL 2158A-listed transition duct within the 8-foot maximum allowed by code. The non-compliant booster fan was removed from the duct run entirely, eliminating the blockage and the fire and CO hazard it represented. The exhaust path through the garage was restored to continuous rigid metal duct, and all joints were sealed with UL 181B-FX rated metal foil tape. Upon completion, airflow was verified at the termination cap to confirm unobstructed exhaust to the outside.