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Thread: Mold on outside of Plenum

  1. #1
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    Mold on outside of Plenum

    Good afternoon,

    I am a new member. I'm hoping this can go in this section of the forum.

    Just moved into a new place and i have an ac company coming out tomorrow. I noticed, what i believe to be mold grown on the blades of the ac vent, which i cleaned off. However, when i checked the ac handler closet, the plenum has what appears to be mold growing along the top where the plenum meets the ceiling. No mold growth visible on the ceiling, just the plenum itself. The ac company said they'll look at it and also do a complete maintenance on it.

    My question is being in south florida- is mold growth on the plenum a common issue? Why would it be there? Will they need to replace the entire thing? Does this mean its inside the unit itself and the kids are breathing it? I have so much anxiety about this as mold really scares me and i worry about having small kids breathing it.

    Any info would be so helpful. Thanks! Pic of issue attached.
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  2. #2
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    I can only say that it would have to be tested to know for sure. Many different things/causes if it is/ are possible and an online search will also help to learn more about it.

  3. #3
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    The surface temperature is below the Dew Point. Typically from Oversized equipment on Undersized ducts, dirty evaporator coils and or fans, restrictions in the supply and or returns.


    Choose the contractor carefully!

  4. #4
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    Quote Originally Posted by pecmsg View Post
    The surface temperature is below the Dew Point. Typically from Oversized equipment on Undersized ducts, dirty evaporator coils and or fans, restrictions in the supply and or returns.


    Choose the contractor carefully!
    Does that mean humidity is the issue? Can this all be taken care of by the ac contractor? He seems to know the townhome well as he lives in the same community and services many.

  5. #5
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    Quote Originally Posted by AC Ignorant View Post
    Does that mean humidity is the issue? Can this all be taken care of by the ac contractor? He seems to know the townhome well as he lives in the same community and services many.
    If he knows what he's doing Yes!

  6. #6
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    Thread Starter
    Quote Originally Posted by pecmsg View Post
    If he knows what he's doing Yes!
    I'm just worried the mold wont be taken care of. The rep I spoke with on the phone said they are doing a complete maintenance on it and if mold is found inside they can spray it with mold killer. I'm just wondering if they'll make me clean the plenum or if they will

  7. #7
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    Quote Originally Posted by AC Ignorant View Post
    I'm just worried the mold wont be taken care of. The rep I spoke with on the phone said they are doing a complete maintenance on it and if mold is found inside they can spray it with mold killer. I'm just wondering if they'll make me clean the plenum or if they will
    In my area we are not allowed to say Mold much less licensed to remove it.

  8. #8
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    Thread Starter
    Where are you located?

  9. #9
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    Quote Originally Posted by AC Ignorant View Post
    Where are you located?
    In South Florida also.
    Mold is a special issue. Need a license to state, discuss and remove.

  10. #10
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    General humidity is going to cause such a problem with mold where you are. Have you looked at extractors for a short term dry out?

  11. #11
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    Most homes in green grass climates are on the edge of growing mold. 50% of the occupants are not sensitive to this level of mold. <10% of the occupants may have a serious response to these low levels of mold.
    I suggest cleaning the spots up with soap and water. Avoid over-cooling below 74^F with the a/c. Monitor the indoor %RH/temperature. If you are unable maintain <60%RH will maintaining 75^F, suggest further investigation/discussion.
    Also comfort issues and allergic reactions. Dust mites and mold are most common problems.

    Get a temp/%RH meter Amazon/Home Depot are sources.
    Your a/c should be setup to provide 75^F, 50%RH on a hot day. A good a/c tech should understand this adjustment.
    Keep us posted what the temp/%RH readings are after you are settled and have the a/c checked.
    The top comfort and indoor air quality systems in a green grass climate involve adding a small whole house dehumidifier to a correctly setup a/c. This done right will eliminate any indoor air quality and comfort issues.
    Most live with minor problems unless serious.
    Get the a/c checked and monitor temp/%RH.
    Keep us posted.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
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    I have seen duct board with mold on the outside of the duct in hot attic and with no mold inside the duct. Usually it's duct tape has came loose or a joint not sealed and air is leaking outside of the duct.

  13. #13
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    Quote Originally Posted by pecmsg View Post
    In South Florida also.
    Mold is a special issue. Need a license to state, discuss and remove.

    I thought you lived in New York?

  14. #14
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    Quote Originally Posted by Deathpunch0311 View Post
    I thought you lived in New York?
    I believe Florida also.

  15. #15
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    Moved to AOP.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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