HVAC Duct Cleaning in San Mateo, CA

What actually loads up ducts in San Mateo homes

Two things drive it here. A long rainless season grinds fine grit into the air, and arterial traffic near El Camino Real and the 101 corridor keeps it suspended. That dust settles in horizontal runs. Then winter fog arrives. Crawlspaces under 1940s–60s ranches stay damp, and bare galvanized trunk lines run cold. Condensation forms on the metal. Wet dust is what grows mold, not clean sheet metal.

Attic flex duct fails differently. The inner liner pulls loose at the boot collar. Insulation fiber and attic dust get drawn straight into the supply stream. Cleaning that duct without reattaching it is wasted work.

We open the system before quoting anything. That means pulling registers, checking boots, and looking at the return. Older homes here often have one undersized return. High static pressure makes air bypass the filter edges, so dust reloads quickly after any cleaning.

Gravity-furnace conversions deserve a separate look. Oversized old trunks reused for a modern blower move air too slowly to self-scour. Debris just sits.

Rodent nesting changes the scope. So do painted-over registers. Wildfire smoke residue on coils does too. Sometimes the honest answer is duct replacement, not cleaning.