Air Duct Mold Removal in San Jose, CA

Where duct mold actually shows up in San Jose homes

This valley is dry enough that attic ductwork rarely grows mold. Dust, yes. Insulation fiber, rodent droppings, wildfire soot in late summer. But not mold. The real finds are underneath: crawlspace supply runs in Willow Glen and Naglee Park-era houses, where ground moisture meets cold sheet metal. The other find is the coil and drain pan. That's the same story in every neighborhood.

Mechanism matters. A plugged condensate drain leaves water sitting in the pan. The blower pushes air across it. Growth starts at the coil face and moves into the supply plenum, not the far branches. A musty hit that appears only when cooling runs points there, not at your registers.

Removal depends on the surface. Original galvanized trunk can be cleaned and stays clean. Brittle gray flex liner and fiberglass duct board are porous. Scrubbing tears them and releases more. The honest answer on those runs is replacement, not cleaning. No sprayed coating changes that.

Check it yourself first. Pull one crawlspace register grille. Look at the boot and the first foot of duct. Panned joist returns in older homes draw unfiltered crawlspace air straight into the system, so sealing those often matters more than any cleaning.