Options for 3inch duct bathroom fan replacement

Old 09-10-19, 09:55 AM
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Options for 3inch duct bathroom fan replacement

Our current bathroom exhaust fan (pictured) doesnít do a great job exhausting shower steam.

Iím reluctant to change the 3 inch ducting. It unfortunately vents through the attic ridge vent. Attic is tall...not sure how I would even go about changing the ducting to 4 inch (or larger).....as I would be unable to reach the ridge vent.

Venting through a side gable is an option, but not looking forward to cutting into gable and/or walking in the attic as the joists are buried deep in insulation.

Basically looking for a grade B solution.

Can I replace existing fan internals that will work with the existing shroud? Should I look for a more efficient fan with 3 inch ducting?

Current fan is rated at CFM 50. Would A change to 70CFM be noticeable?
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Old 09-10-19, 11:56 AM
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First, venting a bath vent fan "to" an attic vent is not permitted as the exhaust is so easily blown back into the attic. It should have it's own dedicated exhaust to outside. Going through the roof or soffit or side wall is commonly done.

You aren't going to have many options for fans that work with 3" ducting as most use 4". Also, since 3" is an oddball small size it appears the fans available tend to be the less expensive, less powerful models. Your best option would be to install new 4" ducting. Then you will have many fan options.
Old 09-11-19, 06:15 AM
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IMO you should never purchase a fan under 100cfm. Even the smallest of bathrooms that isn't to big.
Old 09-11-19, 06:54 AM
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As Pilot mentioned, best bet is to go with a new 4" duct.
We had tossed in a 3" fan in our guest bathroom as we needed to get a bathroom functional during the early days my current reno project. After 2 years, it was near death. Right from Day 1, it never moved much air.

As for your ducting, if going into the attic, depending on where you are located, insulate the pipe if it can get below freezing there and use ridged pipe. Ridged pipe will help with better air flow helping the fan last longer and move more air.
I believe there are some codes in most areas regarding type of pipe, but speaking from personal experience (one of those I'll fix later items), hot moist air collects in those flex pipes and freezes.Potential for mess.

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