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  • Humidity Sensor Location

    I started using some Sonoff TH10 that I flashed with the Tasmota firmware for monitoring temperature and humidity around my home. I have the values reported via MQTT and things are working great.

    However, I moved my sensors from the temporary location which was just somewhere in the room to what I thought was a better location.

    I have a sensor mounted in my HVAC return duct. I also have a sensor mounted in each of my bathroom exhaust fans.

    The temperature and humidity swings are pretty drastic now. Also, the humidity is in the 90s as opposed to it being about 50-60% when the sensor was elsewhere in the room.

    Any thoughts or suggestions? I have spray foam insulation on the roof surface and this is a one-story house. My guess is the spray foam insulation isn't keeping the attic as cool as the rest of the house. And as the warmer humid attic air meets the cooler exhaust fan there is an increase in humidity.

    I imagine insulating the exhaust fans in the attic might help.

    For the last few months, I had my bathroom fan come on and off automatically with the humidity. If the bathroom humidity was more than 15% higher then the sensor under the sofa turn on. And when it was less than 10% different it would turn off. It worked perfectly. I tried to optimize the sensor location (and my wife wasn't thrilled with it just hanging on the counter) and now I discovered this "issue."


  • #2
    In our situation, we put the humidity sensors near the water source (think shower) and away from the exhaust fans because once they turn on, the actual room humidity drops drastically and is not correct.
    Michael

    HS3 Pro 3.0.0.470 | 849 devices | 349 events | OpenSprinkler | BLShutdown | EasyTrigger | NetCAM | Harmony Hub | Sonos | SDJ-Health | BLUPS | PHLocation | BLBackup | BLLock | Z-Wave 3.0.1.243 | weatherXML | Pushover 3P | Blue-Iris | AirPlaySpeak

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    • #3
      Originally posted by JohnGalt View Post
      Any thoughts or suggestions? I have spray foam insulation on the roof surface and this is a one-story house. My guess is the spray foam insulation isn't keeping the attic as cool as the rest of the house. And as the warmer humid attic air meets the cooler exhaust fan there is an increase in humidity.
      You are exactly right.. The sudden rush of cool, conditioned air meeting the humid, warmer air in the return/exhaust ducting is causing the sudden spike in humidity and likely giving you a false reading. (Think of opening a freezer door, which has super-dry cold air inside, and the resulting fog cloud you see come rolling out when it collides with the warmer room air.) I would locate the sensors somewhere near the center of the room where there is some air circulation, similar to how HVAC controls are usually located. Except maybe behind a curtain or under a shelf if you want them less visible.

      Large swings in humidity can cause issues. I have my Honeywell whole-home dehumidifiers set to turn on with a 5 point movement above the target of 55%. Larger swings are not friendly to hardwood floors, wood moulding and trim work, and they make the home AC have to work harder to keep the house comfortable. When you have large swings in humidity, wood trim is constantly expanding/shrinking as the moisture content changes and you will prematurely have to recalk your moulding. Hardwood floors are also more apt to develop squeaks and creaks as they expand and contract.

      --Barry

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      • #4
        Thanks for the comments.

        I think the main issue is my house is old, poorly insulated and very leaky. I don't think I would be able to get the humidity down to 55% during the summer even with a dehumidifier running all the time.

        The mounting locations for the sensor in the bathroom aren't great. However, I will try some better options. I might also try insulating the exhaust fans.

        If all else fails I can try to use averaging, offsets, etc. to determine when to turn the fan on and off. I don't really care about the exact humidity. I just need to know when there is a change (the shower turned on) and when it returns back to "normal." I would rather have clean data in, but we will see.

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        • #5
          In our case, we put the humidity sensors close to water sources and away from exhaust fans. This is so because once they are turned on the humidity drops off naturally.

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