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Community and Q&A

Bathroom Exhaust Outlet Size and Airflow

kevinjm4 | Posted in General Questions on

If your bath fan has a 4” outlet on it, is there any benefit to increasing it to a 6” immediately and carrying that all the way to termination or is the initial 4” at the fan just going to act as a bottleneck…?

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  1. Expert Member
    BILL WICHERS | | #1

    On an unsually long run, upping to 6" can help with airflow. For more typical short runs, there is little benefit to going up a size in duct. Larger duct does provide less backpressure per unit length for a given airflow compared with smaller duct.


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