Duct Sealing in San Jose, CA

What duct sealing actually fixes in a San Jose house

Gray smudges around the register faces. One bedroom that never cools. Dust back on the furniture two days after cleaning. Those usually point at leaks, not at the equipment. Return-side leaks are the worst offenders. A leaky return in a vented attic pulls attic air, and that means dust, loose insulation fiber, and whatever wildfire ash settled up there.

Sealing is mastic, not tape. Cloth duct tape on 1950s-80s galvanized trunk-and-branch dries out and curls off the joints. We brush mastic over seams, use mesh at wider gaps, and band flex collars properly at the boot. The boot-to-drywall joint leaks more than people expect. Attic traffic from solar and electrical retrofits knocks flex off those boots regularly.

Some ducts are not worth sealing. Aging fiberglass ductboard plenums shed fibers as the binder breaks down. Mastic on the outside does nothing for that. In-slab perimeter runs in older slab tracts cannot be hand-sealed, and winter water intrusion makes rerouting overhead the honest call. Uninsulated crawlspace metal needs insulation too, or you just trade leaks for condensation.

Check it yourself first. Hold a tissue at a visible joint with the blower running.