Air Duct Replacement in Sunnyvale, CA

Does the whole duct system need replacing, or just some runs?

Usually not all of it. In 1950s-70s Sunnyvale tracts, the galvanized trunk is often sound. The round branch takeoffs and flex are what fail. Crushed runs in tight attics. Boots pulled loose from register framing. Old cloth tape on sheet metal joints, dried and lifting. We replace the branches and reseal the trunk. That is a different job than a full tear-out.

Full replacement makes sense in specific cases. Gray flex liner shedding fiber inside. Fiberglass duct board plenums eroding at cut edges. Rodent contamination in crawlspace runs under pre-1950 Peninsula bungalows. Those do not clean. They get removed.

Replacement is also the moment to fix sizing. Hall return filter slots here are undersized. Air bypasses the filter edges. The blower wheel and evaporator coil load up anyway. A new return and properly sized grille solves more than new flex does.

Eichler-type homes are their own problem. Slab radiant, no ducts originally. Retrofit ducted heat pump systems get squeezed into attic space or soffits. Routing drives that job, not duct material.

Plan replacement around other work. After attic insulation, a re-roof, a remodel, or rodent remediation. Doing ducts first wastes the work.