Air Duct Repair in Sunnyvale, CA

One room stays hot and the registers blow dust

That pairing usually means a duct came apart, not a bad furnace. In 1950s-70s Sunnyvale tracts the galvanized trunk sits in a vented attic. Round branch takeoffs feed flex runs. The flex pulls loose at the boot. Conditioned air dumps into the insulation. The return then draws attic dust back at you. Look for gray-blackened insulation around the register box. That stain is the leak telling on itself.

Repair work is mostly joints. Cloth tape on old sheet metal dries out and lets go. We strip it and seal with mastic and mechanical fasteners. Crushed flex in a tight attic gets re-run, not taped. Fiberglass duct board plenums erode at the cut edges and shed; those edges need sealing or the plenum needs rebuilding. Uninsulated metal boots sweat on cool summer nights during AC runs, so they get wrapped.

Crawlspace ducting in older Peninsula bungalows fails differently. Rodents chew liner and nest in it. Foothill-adjacent homes see this most. After rodent remediation, assume damaged runs.

Check your hall return slot too. Undersized slots let filters bypass. Then the blower wheel and evaporator coil load up, and airflow drops everywhere at once.