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Community and Q&A

Three bath fans with one outlet

RyanMT | Posted in General Questions on

I want to stick a constant inline vent fan in the attic next to the roof cap vent and then tie my 3 bathrooms to this fan and instead of just a vent in each bath I will instal bath fans in each bathroom.  Some of the vent lines will be about 20 feet long getting to the inline fan and one will only be about 5 foot.   My thought is the main inline fan will be pulling air from all three baths constantly getting fresh air into the house drawing to multiple locations.  Then when we take a shower or have odors we can turn on the vent fan in that bathroom being used and this will make it so the bath fan will pressurize the one line going to the inline vent in the attic and then the inline fan will be pulling air mainly from the one bathroom and will not matter if it is the longest line.  I am thinking a 90 cfm for the inline and maybe 50 cfm in each bathroom.  Will this work?

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  1. Tom May | | #1

    Why would you want a fan running continuously? If you want fresh air, open a window. You may want to learn a little about fluid dynamics first, if you turn on a bathroom fan you may create a venturi drawing extra air from the other two units or pushing air into those units and back into the house if their damper gets stuck open.

  2. Expert Member
    Peter Engle | | #2

    It would probably be cheaper/easier to just use an inline fan with a boost mode that you can trigger with a switch from each bathroom. Yes, it will pull from all three bathrooms in boost mode but that's not necessarily a bad thing. Use a timer so the boost mode reverts to regular operation after a set time. If you are thinking that the always-on part will provide the necessary ventilation for the house, you should calculate its capacity based on IRC or ASHRAE ventilation standards.

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