Increasing the duct size of my bathroom fan outlet?


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Old 09-12-17, 08:35 AM
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Increasing the duct size of my bathroom fan outlet?

I have a new bathroom fan that I'm installing that is 70 CFM. It will only be in the water closet part of the bathroom as the bathroom already has a larger 150 CFM fan in it.

The 70 CFM fan has a 3 in. duct outlet. I was wanting to use insulated ducting to run to the outside of my house but can't find any locally and am not finding many options online either.

Am I ok in using a 3 inch to 4 inch duct increaser to attach a 4 inch duct to my fan or would I be causing some issues with the air movement?

The duct will be about 12 feet in length and will have a pretty strait shot venting out through an exterior wall.
 
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Old 09-12-17, 09:42 AM
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Increasing the size of the duct from 3" to 4" is ok.
Just check and make sure your fan has enough strength to open a 4" vent.
 
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Old 09-13-17, 12:25 PM
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Increasing exhaust fan duct size

I have a bathroom exhaust fan that has a 3 inch duct outlet. However, I would like to use a 4 inch insulated flexible duct.

Is there an adapter I can use to accomplish this or do I have to first use a short run of 3 inch duct and then use a 3-inch to 4-inch increaser?
 
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Old 09-13-17, 12:55 PM
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Threads combined...........

Not sure if there is an off the shelf adapter but you could use a short piece of 3" and 4" PVC with a reducer/coupler.

I see the depot sells a pre-made tin adapter. You could wrap it in insulation after connection.
4 in. To 3 in. Round Reducer-R4X3 - The Home Depot
 

Last edited by PJmax; 09-13-17 at 01:13 PM.
 

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