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Thread: High Humidity in house

  1. #1

    Default High Humidity in house

    We have recently figured out the our bathroom exhaust fan has been blowing in, instead of out. We had this reversed(corrected). We have now seen an increase in our humidity within the house. We are at 60%. We believe that we have outside air coming in from somewhere, but we don't know where.

    We have to run our A/C at 72 degrees in order to bring the humidity level down to about 55%.

    Does anyone have any suggestions.

    Thanks,
    Doug

  2. #2
    DIY Senior Member SteveW's Avatar
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    What part of the world do you live in?

    What is the outside temperature and humidity?

  3. #3

    Default High Humidity in house

    Steve,

    We live in Bradenton, Fl. This is about 50 miles south of Tampa.

    The outside temperature is about 73 degrees and the humidity is about 85%.

    We know that our house needs to stay below 60% humidity. Before we had the bathroom vent fixed we were at 52%. We are feeling a lot of cold air coming through the supply ducts(vents). Last week when it got somewhat cold overnight, our bedroom windows developed condensation on the inside of the windows. This is not normal.

    We are now going to have a blower door test next week.

    Any suggestions.

    Thanks,
    Doug

  4. #4
    Electrician Chris75's Avatar
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    Quote Originally Posted by Doug R View Post
    We have recently figured out the our bathroom exhaust fan has been blowing in, instead of out. We had this reversed(corrected). We have now seen an increase in our humidity within the house. We are at 60%. We believe that we have outside air coming in from somewhere, but we don't know where.

    We have to run our A/C at 72 degrees in order to bring the humidity level down to about 55%.

    Does anyone have any suggestions.

    Thanks,
    Doug
    Wanna explain this with more detail, because I just dont believe you.

  5. #5

    Default High Humidity in our house

    Chris,

    No disrespect, but this is a true story. We purchased the house about 5 months ago. It is a brand new house that was on the market for 2 1/2 years because the market was so bad. Our original home inspector did not do a good job. After we bought the house, my wife and I noticed that the bathroom vent was blowing air down at us. This is when we decided to have the house re-inspected to see what was wrong. This new inspector said that the fan was blowing in the wrong direction.

    With regards to the air coming from the supply vents, we just don't know about this. We are going to have a blower door test and duct test to see if we have any leaks.

    If you have any knowledge about this, please share. the humidity is now at 54 degrees as we have our thermostat set at 72 degrees.

    Thanks,
    Doug

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    While not all that common in residential units, a HVAC system with reheat may be called for if you want to keep the humidity within a certain range where you live. This is probably the hardest time to keep it in check - when the outside temp is near the desired interior temp...to remove humidity, you run the a/c, but then it's too cold so you run the heat. A system with reheat can run both heat and cooling simultaneously so you don't get blasted with really cold or hot air, making it much more comfortable. Just by it's nature, it's an energy hog. In that environment, you might want to try just some dehumidifiers, and keep the main HVAC system off. They're nearly neutral since they cool the air, but then blow the exhaust heat out (normally into the same room). The heat rise is what's left over in the inefficiency of the process.

    Unless the exhaust fan for the bathroom is a remotely mounted in-line fan, they it's basically impossible to have it run backwards unless you take it apart before installation and change it yourself.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    Like an engineer alternety's Avatar
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    When you do the blower door test, use smoke to track leaks.

    Make sure joints in ducts are properly sealed. Foam any hole leaving the envelope (pipes, wires, top of walls (in attic) ). Make sure everything leading outside has a good seal or add weather stripping.

    I am guessing there would be a tendency for builders in that climate not to pay the kind of attention to building sealing as we do in the frigid parts if the US. That is wrong; for the reasons you have discovered.

    Also see if the duct system has some sort of fresh air intake. It rather sounds like your air conditioner is creating negative pressure in the house.

    Right now I could use hot and humid. I would be glad to mail you a house full of dry warm in exchange for one of your house fulls of warmish and humid.

  8. #8
    HVAC Contractor Marc46's Avatar
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    You may also have leaks in your return trunk lines in the attic, which are pulling in the humid outside air.

    The exhaust fan makes no sense,.......if it was introducing outside air before, you should have improved the humidity situation by correcting it.

    As the other poster said, with the run time on the system so short now, and relatively high humidity for this time of year,.........you aren't getting the run time needed to remove the humidity, without freezing your keester off.

    I am a few hours north of you BTW.

  9. #9
    DIY Junior Member ROLLIE8271's Avatar
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    Default ???

    Doug,

    What happen with your humidity problems? I am having similar problems in my house and was wondering if yours was resolved.

    Thanks,

    Rollie

  10. #10
    DIY Senior Member Runs with bison's Avatar
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    Assuming that your AC is running some, you want it to run in its lowest stage with minimal blower flow. (Lowest stage results in longer run time, lower blower flow = more subcooling and dehumidification.) This will subcool the air more resulting in greater dehumidification. Higher blower flow rates result in little dehumidification. Of course, you want to minimize air infiltration as well. If you are near a balance point with outside air temp and the AC is rarely running, but leaving you hot and sticky, then lower the temp a degree or two until it begins to dehumidify and improve comfort. You can raise set points later as the air becomes drier.

  11. #11
    In the trades Dana's Avatar
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    I hate responding to long-dormant threads- I'd be happier if ROLLIE8271 would have started a separate thread.

    In a FL climate the latent loads of summertime ventilation air are quite high, and well-insulated/low solar gain but poorly air-sealed home end up with high indoor humidity in summer due to unwanted air infiltration and low air-conditioning duty cycles.

    Vented crawlspaces with poor air sealing between the crawl & conditioned space is one common source. Poor air sealing between attic & conditioned space is another. If unsealed ducts &/or air handler live in the attic, pressure differentials generated by the air-handler itself can also drive huge volumes of infiltration on the house itself, which would consequently require longer duty cycles to bring the humidity down.

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