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In our master bathroom we have a smaller room with a door where the toilet is. This smaller room contains a vent fan. The larger area where the shower and sinks are doesn't have a vent and gets very humid.

Is it possible to install a vent fan in the shower area and just hook it up to the other vent fan’s exhaust ductwork?

All vent fans are single units where the fan is located within the vent in the bathroom.

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    Is this "vent" just a hole, or is there a fan in the vent? Is the fan at entrance to the vent, or is it an inline vent (i.e. grille - ductwork - fan - ductwork - grille)?
    – AndyT
    Apr 11, 2018 at 8:57
  • There is already a working fan in the vent, with the fan within the vent, and not in the duct work.
    – CM10
    Apr 12, 2018 at 1:11
  • A one piece unit placed in the ceiling cut out, and then ducted up through the roof-
    – CM10
    Apr 12, 2018 at 1:47

2 Answers 2

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I would not recommend this. If one fan is turned on and the other isn't, the fan that is on could send humid air backwards through the other fan (unless it has a working non-return valve).

I would advise either ducting this new fan completely separately, or instead getting an inline fan with a Y-piece to allow it to vent from two seperate grilles. See hvacquick.com for this example:

image of inline fan venting two bathrooms

NB This is not a recommendation of a particular product/supplier/manufacturer

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  • The Y Piece would have to have a back flow preventer .
    – Ken
    Apr 12, 2018 at 9:18
  • @Ken - No it wouldn't, because when the fan is running it is drawing air through both legs of the Y. In order for air to travel the wrong way down one leg of the Y, it would have to be travelling against the force being exerted by the fan.
    – AndyT
    Apr 12, 2018 at 9:21
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    @Ken - For clarity, my picture shows an inline fan beyond the Y piece, with grilles only in the bathrooms. Hence why there is no need for a backflow preventer / non-return valve.
    – AndyT
    Apr 12, 2018 at 11:37
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You can do this. Another answer stated they don't recommend it.

You need to ensure that the two fans don't exhaust into the other area and simply exhaust out through the roof. With a proper one directional airflow vane in the duct you can accomplish what you would like to do. However in many installations you might not find this - you might simply find a connecting pipe to the vent and the pressure of the fan will force the air through the roof vent as the path of least resistance.

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  • What would happen if both fans were hooked to the same electrical line so if one is on, they both are on?
    – CM10
    Apr 12, 2018 at 22:21
  • @CM10 they would both run. However if you use Andy's Method of a Y with the fan after the Y then both areas would have ventilation using one fan. Cheaper and Easier since the fan is already wired up - if it has enough slack that is, other wise a $4 junction box and a few feet of wire and you are done.
    – Ken
    Apr 13, 2018 at 2:00

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