Air Duct Replacement in San Jose, CA

When does duct actually need replacing instead of sealing?

Ask the installer to show you the inner liner. Brittle, flaking gray or black flex from the 1970s through the 1990s cannot be sealed back to useful life. Attic heat cooks the liner. It cracks at every bend. Mastic on a failing liner buys months. Replacement is the honest answer there. Original 1950s and 60s galvanized trunk is different. Sheet metal often survives fine. The wrap around it does not. Paper-backed insulation of that era can contain asbestos, so it gets tested before anyone disturbs it, not after.

The faults that drive full replacement here repeat often. Crushed flex behind attic storage boxes. Boots pulled loose at ceiling registers, dumping cooled air above the drywall. Panned joist returns in older homes pulling unfiltered attic air straight into the blower. Undersized filter slots where a 1-inch filter bypasses at the edges.

Replacement means new R-6 or R-8 flex, new boots, sealed metal plenums, and a return path sized to the equipment. Static pressure gets measured, not guessed.

Crawlspace runs in Willow Glen and Naglee Park-era homes are the exception on moisture. Attics here stay dry. Crawlspaces do not. Mold there is a replacement trigger on its own.