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Reducing noise transfer between rooms through ducts

DarkNova | Posted in General Questions on

In our current house which has all rigid metal ducts, noise transfers easily between rooms through the ductwork. For our new house, I want to make sure that the HRV ductwork does not have the same problem.

Flex is often maligned but it seems as though it could be useful in limited quantities. Based on what I read here, it seems that running a short section from the metal trunk to each room, while making sure the section is straight, pulled tight, and sized for the proper airflow (which probably makes this section upsized from the metal diameter), should not cause a problem.

I’ve heard anecdotal that including a small section of flex duct in this manner will reduce noise transfer between rooms. But I’m not sure how much is ideal. Does anyone know of any data or experiments they have done on how much flex duct is needed for this purpose? I’ve heard 8′ but that is a pretty random number, I don’t know if it is based on anything. Thanks.

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  1. JC72 | | #1

    Risinger Homes uses flex for the last 6' or so. He posts a lot of energy efficient videos with regards to his builds.

  2. gozags | | #2

    Go to and look in the dedicated theatre forums. There are soundproofing threads and if you have specific questions you can sign up and post them. For the most part the advice tends to lean towards the 'sound' half of the spectrum but there seems to be plenty of concern regarding performance of the hvac systems.

  3. DavidGutowski | | #3
    This flexible duct connector material would probably be a good choice to decouple the metal ducts and prevent the "microphone effect".

  4. DarkNova | | #4

    Thanks all

  5. charlie_sullivan | | #5

    1. Zehnder uses "home run" ducts. That should pretty much eliminate the problem.
    2. Lunos makes ductless HRV/ERV systems. That truly eliminates the problem.

  6. user-626934 | | #6

    If it's just a short section of flex-duct, well supported and pulled tight, then it's likely unnecessary to increase the duct size. The vast majority of resistance in duct systems is from fittings and filters...not from straight sections of duct.

  7. Expert Member
    Michael Maines | | #7

    There are various duct silencers available, which work like a muffler on a car. I don't know how they compare to flex duct but since they are made for the purpose I have to think they work better.

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