I have two bathrooms fans in the same bathroom to help with mold problems. They are wires to the same switch. One runs continuously even when the switch is off. Why?

  • 5
    Because it is not wire correctly. Without details and pics of the wiring at the fan and switch, that is as detailed as one can get.
    – RMDman
    Feb 24 at 4:53
  • 3
    clearly they are not wired to the same switch
    – Tiger Guy
    Feb 24 at 5:56
  • 3
    If they are wired to the same switch and one is controlled by the switch and one not, then the latter is wired to the always hot side of the switch. Or the one not controlled is wired to power in addition to being wired to the switch. Feb 24 at 13:12

1 Answer 1


Presumably the one that runs continuously is intended to do that to "help with the mold problem" and the other is supplementary to deal with large amounts of moisture from showering, etc.

As has already been mentioned in comments, this is as simple as one gets power from the un-switched hot at the switch, and other gets the switched hot at the switch, if they are "wired to the same switch."

This is fairly common in newer houses built tightly sealed, and not uncommonly the continuous fan might be connected to a heat recovery ventilator or energy recovery ventilator, with the bathrooms being a default location for the exhaust intake of those systems.

For mold remediation in a house that's not so tight, it might just be a straight exhaust fan to keep some air moving through and deal with the mold issue.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.