Duct Sealing in Santa Clara, CA

Why sealing fails first at the joints, not the duct

Back bedroom never gets warm. Dust returns two days after cleaning. The duct is usually fine. The joints are not. Cloth-backed tape dries out in attic heat. The adhesive gives up and the seam opens. Conditioned air then heats your attic instead of your house.

Leak points here are predictable. Flex collars at the takeoff, where the drawband slipped off the beaded fitting. S-slip and drive cleat seams on old galvanized trunks in crawlspaces. Corner joints on fiberglass ductboard plenums in some 1970s builds. The furnace base and the return plenum, which is the one that matters most. A leaky return pulls crawlspace or garage air past the filter. That is unfiltered air going straight to your registers.

Sealing is mastic and mesh on metal, mastic and a mechanical band on flex. Foil tape rated for ducts has a place, but not alone on a joint under tension. Everything gets reachable first. We open the crawlspace access and pull back insulation at the takeoffs.

Some runs cannot be sealed honestly. Crushed flex under stored boxes gets replaced. Rodent-chewed liner too. A kinked run folded over a truss chord gets re-routed. Sealing a collapsed duct buys you nothing.