Bathroom vent fan size- too big?


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Old 04-15-15, 06:06 PM
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wgc
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Bathroom vent fan size- too big?

I have a question about sizing a bathroom vent fan that I was hoping someone could help with, but from the opposite direction ...

I have a small bathroom, about 42sq ft with an 8' ceiling, with a shower. The previous vent fan was 70 cu ft/min and seemed sufficient but I need to replace it (motor went but the fan is old and noisy). It is a large rectangular unit with heat and a light - I want the same, only quieter.

The problem is most vent fans with those features are 100 cu ft/min or more. That is twice the recommended flow for such a small bathroom. What are the downsides of too much ventilation and would I regret going so high? Would it need larger ductwork and more makeup air or is it really not that different?
 
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Old 04-15-15, 11:56 PM
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I think the "recommended" airflow for bathroom fans is way lower than it should be so I would not hesitate going with the 100 CFM fan. Yes, you will need more make-up air and likely a larger duct as well.

Just my opinion.
 
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Old 04-16-15, 03:45 AM
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Is the current duct work 4"? If it is That should be fine for a 100cfm bathroom fan.

I don't think you'd regret going bigger
 
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Old 04-16-15, 05:45 AM
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Would there really be an issue if the ducting is too narrow? It seems like having it too narrow would make the fan less efficient (irrelevant in a bathroom this size), and at most be a minor strain on the motor.

(asking questions, not making statements)
 
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Old 04-16-15, 12:34 PM
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I 100% agree with furd. These CFM ratings are to low. It will most likely take a 100cfm fan 30-60 minutes to remove moisture after showering.
 
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Old 04-16-15, 05:11 PM
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Cool

Yes, it is 4" ductwork.

Thanks for everyone's opinion that I wouldn't regret going bigger. It gives me more choices and even saves money over trying to get closer to the recommended size.
 
 

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