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Community and Q&A

Bath fan venting

kevinjm4 | Posted in General Questions on

I have a Panasonic I am now stuck with since I can’t return. I say stick because I do not like the 3” oval outlet. My question is this: will transitioning from the 3” oval to a 4” round, then to a 6” round be beneficial, or will the 3” oval act as a bottleneck and no matter how large my duct is after the fan it won’t matter.

In other words, will a 4” and a 6” round operate the same if the beginning of the run is a 3” oval.


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  1. Expert Member


    The outlet is almost always 3" or 4", whether round or oval. Transition to whatever size duct will reduce your friction loses and reduce noise.

  2. Expert Member
    Akos | | #2

    The outlet on the Panasonic is a 4" oval, it is not as restrictive as it seems. This means you can take a length of standard 4" round duct and squish it on one end and it fits right over it, the other end can stay round and go to the outdoors or bump it up a size if you have long.

    If it is the fan I'm thinking of, it is still one of the best low profile units. Good flow and very quiet.

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