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Can I have two different exhaust fans in the same bathroom on the same switch. ? (I.E. on/off at the same time, both ducting to a y-adapter attached to a single roof vent opening).

One fan uses 4" duct and the other a 6" duct, but I was going to use a Y-adapter that is 4" on all three openings and use 6" > 4" reducer for the larger fan duct.

I get different answers from everyone that has looked at it!

Thanks!

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  • Hello, and welcome to Home Improvement. If an answer is helpful, please click the large check mark next to it to accept. And, please take our tour so you'll know the details of contributing here. Commented Aug 13, 2020 at 17:13

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on/off at the same time

Problem ?: NO.

No problem with having two fixtures on the same switch. As long as the combined amp ratings of the fans (and anything else on the same circuit) is below the amp rating of the circuit breaker.

both ducting to a y-adapter attached to a single roof vent opening

Problem ?: Maybe.

Maybe. When bathroom fans are controlled by separate switches it is not allowed to have them share the same duct because one fan will push the humid air from one bathroom to the other bathroom. Will that be the case with both fans on at the same time? All things being equal, fans CFM's, length of ducts, size of ducts it may not be a "problem".

With different size ducts and different fans i can see one causing the other to not work efficiently. (This is speculation on my part, an HVAC tech is the proper person to ask.)

My gut feeling is it is not a good idea.

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    If one of the fans fails, the other will be recirculating the humid air. And the failure probably won't be noticed; the noise from one fan sounds a lot like the noise from two fans. Commented Aug 13, 2020 at 18:18

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