4" Exterior vent ok with 8" bath fan

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Old 07-01-20, 12:48 PM
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4" Exterior vent ok with 8" bath fan

I'm installing a Panasonic 70 CFM whisperwall fan in a basement bath (cannot get ceiling access for ceiling fan).
This unit comes with an 8" exhaust. Distance to exterior wall for venting is about 6'. I recognize many recommend the largest piping possible to facilitate air flow. That said, am I ok venting to a 4" opening or is an 8" opening really needed. Thanks.
 
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Old 07-01-20, 07:39 PM
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That fan appears to have an axial fan, and will probably need that 8" duct. You might want to exchange it for a more traditional centrifugal fan, which can easily move 70CFM through a 4" duct.
 
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Old 07-01-20, 07:44 PM
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Welcome to the forums.

The Panasonic Whisperwall fan is designed to be mounted thru a wall and ducted directly outside.
It's not designed to be connected to ductwork..... just an outside hood.

Whisperwall installation instructions
 
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Old 07-02-20, 05:23 AM
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You do not want to restrict your fan by using a smaller duct. 4" duct may sound simply like half the size of 8" but actually it's much, much smaller if you do the math. A 4" duct has about 12 square inches of area while a 8" duct has 50. The 8" has over four times the area. Using a 4" duct will severely limit airflow.
 
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Old 07-02-20, 12:30 PM
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Thanks all. Appreciate the advice. Haven't ordered the fan yet. Doing homework first. Anyone recommend a centrifugal 4" wall fan? Panasonics came recommended from electrician. We have two in the house that work well.I'm not married to the brand. Thanks again. TK
 
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Old 07-02-20, 01:01 PM
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Any of the Broan InVent wall/ceiling fans would work. They take a 4" duct. When paired with the MFQ4 duct connector, air leakage is considerably reduced... probably more important when the run is only 6 ft.
 
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Old 07-06-20, 06:24 AM
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I've since discovered I can access a different part of the ceiling so I'm back to a ceiling fan. Thank you for the assistance. I appreciate it.
 
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