Air Duct Replacement in San Mateo, CA

When is replacing ductwork the right call instead of cleaning it?

Ask that before anyone runs a brush. Cleaning restores a sound system. It does nothing for torn flex, crushed trunks, or metal that has rusted through. In San Mateo crawlspaces we still find original galvanized trunk-and-branch under 1940s–60s ranches. Winter fog condenses on bare metal. Dust settles, stays damp, and grows mold. No cleaning method fixes that duct. The surface is gone.

Gravity-furnace conversions are the other common replacement case. Oversized old trunks got reused for modern blowers. Air velocity drops, throw is weak, and far rooms never get warm. Resizing the distribution is the actual repair. Returns usually need attention too. Older homes here were built with one undersized return. That drives static pressure up and pulls dust around the filter edges.

Attic flex on 1980s-plus construction and second-story additions fails differently. Boots pull loose. Runs sag between joists. The system then draws attic air, which after wildfire smoke season means fine particulate straight to the coil.

Replacement means new material, properly supported, sealed at every boot, insulated for its location. Rodent-damaged subfloor runs come out entirely. Painted-over registers from past remodels get replaced, not scraped. Partial replacement is often the honest answer: one bad branch, not the whole house.