Duct Sealing in Los Angeles, CA

What duct sealing actually fixes in a Los Angeles house

One bedroom never cools. The hallway grille whistles. Dust films the registers a week after you wipe them. In most of these houses the air is going somewhere it shouldn't, usually the attic. Flex duct pulls loose at the boot. Takeoff collars at the plenum were tacked with cloth tape that dried out decades ago. Panned returns built from framing and drywall suck attic air straight past the filter.

Sealing means mastic, not tape. Mastic with fiberglass mesh on metal seams and collars. UL 181 foil tape on the flex inner liner, then the jacket pulled back over and strapped. Boots get sealed to the ceiling drywall from above, which is where the biggest single leak usually sits.

Older galvanized trunks carry grey or black tape at the joints that may contain asbestos. That gets tested, not scraped. Ductboard plenums from the seventies and eighties shed fiber; sealing a crumbling plenum is a stopgap. Near the coast, damp salt air rusts uninsulated plenum seams, and mastic won't bond to flaking metal.

Watch the return side. Tighten every supply on a house with one hallway return grille and static pressure climbs, so the whistle gets louder. Crushed, detached or rodent-fouled flex gets replaced, not patched.

Check it yourself: look for gray dust streaks in the attic insulation around each boot.