What to know
What decides how long a seal lasts
- The material. Cloth duct tape is not rated for this and fails early. Foil tape with a proper rating does better. Flexible mastic at a prepared joint outlasts both.
- Preparation. Sealant applied over dust bonds to dust, and it will let go regardless of how good the product was.
- Coverage. A joint sealed only where somebody could easily reach is a joint that will leak on the side nobody sealed.
- Movement. Ductwork expands, contracts and vibrates every cycle, so anything rigid at a joint that flexes will eventually crack.
- Environment. Runs in a hot attic or damp crawl space work harder than runs in conditioned space.
What to look for
- Tape curling, discoloured, or hanging away from a joint. This is the most common finding and it is visible from several feet.
- Visible gaps at a collar where a branch leaves the trunk.
- Sealant that has cracked or gone chalky.
- A boot under a register that has separated from the floor or wall.
- Insulation compressed or displaced along a run, which often means somebody has been on it.
The signs from inside the house
A room that used to keep up and no longer does, particularly one at the far end of the system. Weak airflow at distant registers with strong flow near the furnace. An attic or crawl space that feels conditioned. Dust reappearing at a register quickly after a clean, which points at the return side.
What we will not put a number on
How many years any particular sealing job will last. That depends on the material used, how it was applied, and where the ductwork runs, none of which we know about your house from here.
What we can do is look at the accessible connections and tell you what condition they are in now, which is the question that actually matters.
Where to start
Which of these applies to your ductwork depends on how it was built and what shape it is in now, and that is not something a page can settle.
Our inspection is free. We will show you what we find, and if the answer is that your ducts are sound and simply need cleaning, that is what we will tell you.