Problems With Flex Ducts

Take a look at the photos above, do you see anything wrong with the duct work? From far and the untrained eyes, nothing would be wrong with this. Unlicensed contractors may also say the same thing. But to licensed professionals, everything is wrong with the pictures above.

Disconnected ducts, incorrectly hung, sagging, and leaks are just some problems I can name that are visible by these pictures.

When it comes to providing duct work, we tend to stay away from flex ducting. Flex duct has an inner lining made of plastic and wire spirals that can easily bend the duct in any direction. The duct itself is made from soft material. These flex ducts are useful in cramped spaces; however, we tend to stay away from them when we can.

We tend to stay away from flex ducts because of a few things:

  1. If the flex ducts aren’t hung correctly, it’ll cause sagging. Sagging means that the air doesn’t flow in a straight line and causes inefficiency in the air flow.
  2. If the flex duct isn’t pulled tight, it’ll cause high air resistance inside. Also causing inefficiency.
  3. If the flex duct isn’t properly sealed against sheet metal registers, leaks may occur.
  4. Flex ducts are often abused by installers.

If we do have to work with flex ducts, we make sure it’s done correctly: flex ducts must be pulled tight to reduce resistance, straps supporting the ducts should be at least 1.5″ wide, and the straps need to be spaced no further than 5 feet apart. Flex ducts work extremely well when it’s sized and installed properly. Majority of the time though, it’s done wrong.




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