Can a bathroom exhaust fan be oversized?
Remodeling the 2nd story of a 1.5 story Cape, and building a ~110 sqft. master bath. I plan on installing a remote bath exhaust fan (Panasonic Whisperline Remote FV series) and need to choose between the 100 CFM and 200 CFM models. The plan is to have two intakes — one over shower/tub, and an additional about 8′ away above the toilet, and then exhaust out my gable vent about 15′ away to avoid punching more holes in my new roof. I have more than adequate soffit and ridge vent ventilation, so I can afford to sacrifice one gable vent for this.
The 100CFM unit uses 4″ ducting, and I think it will be too restricted pulling from two intakes. 200 CFM unit uses 6″ ducting, so I think I’ll be ok pulling two 4″ intakes, and exhausting through a straight run of 6″ out the gable vent.
Rule of thumb is 1 CFM per square foot, but is there any harm in oversizing? With it being a remote fan, noise won’t be an issue.
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