Conditioned air that leaks out in the attic or crawlspace before it reaches the room is air you already paid to heat or cool.
Duct joints, takeoffs and boots are sealed with mastic or an approved tape at installation, and that seal degrades over years, especially where it sits in an attic that swings between summer heat and winter cold. Once a joint opens, the air moving through it takes the easiest path out rather than continuing down the run to the register it was meant to reach.
This matters more in an unconditioned space than it sounds like it should. Air that leaks into a fully conditioned basement is at least still inside the house; air that leaks into an unconditioned attic or crawlspace is gone. Sealing the plenum connections, the takeoffs and the boots on those runs keeps the air that left the furnace or air handler actually arriving where it was sent.
Describe the problem and we'll tell you whether it's cleaning, sealing, repair, or not a duct problem at all.
Get Matched With a Duct ContractorA short description is enough — we'll follow up to sort out what it actually needs.