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  1. #1
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    Mar 2018
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    Safe amount of setback to avoid condensation with humidifier

    I currently have an Aprilaire Steam Humidifier and was wondering what a safe amount of overnight setback would be to avoid condensation on windows and such?

    Last year I dropped the temp 10 degrees overnight and had some ice forming on windows even though the system has an automatic humidistat set to a pretty conservative setting.

    I attribute a lot of this to the increase in relative humidity due to the decrease in temperature.

    Your input is greatly appreciated!

  2. #2
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    What was the
    RH indoors?
    Temp outside?
    Temp near the glass?

  3. #3
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    Apr 2003
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    Quote Originally Posted by Hvacnewb15 View Post
    I currently have an Aprilaire Steam Humidifier and was wondering what a safe amount of overnight setback would be to avoid condensation on windows and such?

    Last year I dropped the temp 10 degrees overnight and had some ice forming on windows even though the system has an automatic humidistat set to a pretty conservative setting.

    I attribute a lot of this to the increase in relative humidity due to the decrease in temperature.

    Your input is greatly appreciated!
    Condensation/frost on the inside of windows is a complicated issue that depends on outdoor temperature, indoor temperature, indoor humidity, window coverings, and "R" rating of windows.

    It's usually a bit of an experiment to find the right setting that can prevent condensation from forming on those windows. As it gets colder outside, the amount of humidity that you can have in your home without it forming on your windows goes down. Also as you have found out, lowering your indoor temperature also drops the amount of maximum humidity that you can have as well.

    You say you have an "automatic humidistat". Hopefully that means that it has an outdoor sensor and can adjusts the humidity level based on that. If so, your experimenting job should be a little easier. Start by lowering the setting a little more, and then set your thermostat to a set-back temperature of no lower than 60°F (since lower than that isn't good for your furnace's heat exchanger).

    Good luck.
    If at First You Don't Succeed, Skydiving Is Not for You.

  4. #4
    Join Date
    Mar 2018
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    Thread Starter
    Quote Originally Posted by ammoniadog View Post
    Condensation/frost on the inside of windows is a complicated issue that depends on outdoor temperature, indoor temperature, indoor humidity, window coverings, and "R" rating of windows.

    It's usually a bit of an experiment to find the right setting that can prevent condensation from forming on those windows. As it gets colder outside, the amount of humidity that you can have in your home without it forming on your windows goes down. Also as you have found out, lowering your indoor temperature also drops the amount of maximum humidity that you can have as well.

    You say you have an "automatic humidistat". Hopefully that means that it has an outdoor sensor and can adjusts the humidity level based on that. If so, your experimenting job should be a little easier. Start by lowering the setting a little more, and then set your thermostat to a set-back temperature of no lower than 60°F (since lower than that isn't good for your furnace's heat exchanger).

    Good luck.
    Yes, it does have an outdoor sensor. When it gets real cold I also leave the blinds up about an inch to allow the warmer air to access the windows more easily.

    I will try a 5 degree setback and hope that makes the issue a little better than the 10 degree setback.

  5. #5
    Join Date
    Nov 2004
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    SW FL
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    Condensation versus % R.H.

    For a 68'F to 63'F setback,
    a corresponding Relative Humidity reduction may need to be ~ 7%.

    20'F to 40'F ODT __ < 33%
    10'F to 20'F ODT __ < 28%
    . 0'F to 10'F ODT __ < 23%


    Basis of Chart in the link is 70'F indoor temperature
    https://aamanet.org/pages/understand...r-condensation

    What did you discover?
    Blinds likely need to be Open

    * Tips to Manage Indoor Humidity Levels
    Ensure that your home is properly ventilated, especially around those areas where condensation is most likely.

    Just as you would run the defroster in your car, you should turn on ceiling fans throughout the home and run exhaust fans as needed to remove excess moisture.

    Open curtains and blinds during daylight hours.
    Keeping them closed increases the likelihood of condensation forming with potential moisture damage.
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