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Humidity-Sensing Exhaust Fan Connected to Motion Sensor

derekr | Posted in General Questions on

Has anyone ever done this? I’m wondering if it will cause some kind of conflict

like you walk in to take a shower the motion switch activates the fan, after you are done showering and the humidity is in the air, would the humidity turn the fan off since it was already turned on by the motion switch?

also would like some advice on location, since it’s a motion switch would it be better to place it some where else in the bathroom or just put it with the other switches by the door? So I was thinking if you go into the bathroom to wash your hands or brush your teeth the fan would be activated when it doesn’t need to be, thats what I was I thinking if I placed the motion switch somewhere else instead of by the door

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  1. user-5946022 | | #1

    Yes it can be done but you need to be careful to understand what your goal is.

    I have the Panasonic Whisper series with integral condensation sensor. I had them wired to always have power to the fan, and the fan goes on and off via the control wiring.
    - The condensation sensor will automatically turn the fan on if it senses condensation.
    - The switch on the wall can manually turn the fan on an off. Because the wall switch is wired to the fans control wiring, turning it off at the wall switch does not cut power to the fan, so the condensation sensor can still turn on the fan.

    The wall switch acts like a dry contact, so if I wanted I could get a dry contact motion sensor module that also turned on the fan anytime someone triggers the motion sensor. But there is really no need - if there is humidity, the condensate triggers the fan. If it needs to be used as a fart fan, it is manually turned on. The one thing I do want to figure out is a dry contact switch that will automatically turn the fan off after 5 minutes when it is turned on manually.

  2. DennisWood | | #2

    You can accomplish that with a device like the Fibaro Smart Implant:
    but you'll need an automation hub like Hubitat or Smarthings to set this up. That unit has dry contacts and can be programmed to turn them off/on as desired. It also has the option for external temperature and humidity sensors so could manage the fan entirely if desired:

    I use one of these for my pool solar system to host temperature sensors which in turn allow me to manage the system via automation.

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