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Positioning remote bath fan in attic

| Posted in General Questions on

Hi folks. I may be getting caught in the weeds here, but I’m sure an expert here can point me in the right direction…

Installing a Panasonic Whisperline 120 cfm remote bath fan in an attic to vent a 2nd floor master bathroom. The fan will be venting out of the gable vent, to avoid putting holes in the new roof. I have adequate soffit and ridge venting, and will block the gable vent except for the 4″ duct penetration to avoid pulling in any of the moist air I’m trying to vent.

I have two options for mounting the vent fan and routing the ductwork, as illustrated in the attached diagrams:

1. Mounted on top of ceiling joists
2. Suspended from rafters/ridge

If I go with #1, I can insulate the fan and most of the ductwork with the existing fluffy attic insulation. However, I’m concerned condensation could collect in the area indicated by the orange arrow due to the necessary vertical transition of the ductwork here to get up to the gable vent (about 4′ up). 

If I go with #2, I would have to separately insulate the ductwork, but could have a straight run for the exhaust with a downward slope to ensure any condensation does run out the vent. There will still be some near vertical ductwork for the intake, and condensation could run down here, but at least it would drip into the conditioned space where I would see it. 

Considering the ductwork will be insulated regardless of which route I take, am I overthinking the condensation concern here? Not pictured is the fact that I’ll be pulling intake from two locations, so #1 is certainly the path of least resistance and my highest chance of getting the details correct, so that’s where I’m leaning.

Thanks for any thoughts.

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  1. charlie_sullivan | | #1

    Option number 2 sounds safer to me, but I don't see your pictures and I don't know what climate you are in. You could also consider going through the gable wall lower than the gable vent.

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