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Thread: Mold on grills

  1. #1
    Join Date
    Jul 2004
    New Orleans
    Hello - I'm hopeful someone can offer advice. We purchased this house three months ago - it is approx. 60 years old, galvanized/metal duct work was probably installed in the mid 60s. The HVAC unit itself (Carrier A/C - Furnace combo) is probably 3-5 years old and includes a UV light system that is located at the return according to the A/C tech sent by the home warranty company.

    Approx. 6 weeks ago we noticed mold growth on the grill in the downstairs bathroom. We returned from one-week vacation at the end of June and mold is now on almost all of the grills although not as bad as what is in the bathroom (temp on A/C was 80 degrees while we were gone if that makes any difference). The A/C tech sent by the home warranty company says that the unit is in fine shape and that he suspected mold in the duct work. The home warranty says such work is considered routine maintenance and is not covered.

    We called 2 duct cleaning companies - both reps said we have mold in duct work (neither removed even 1 grill) and offered to clean the duct work for between $700-850 using vacuum/big brush method that is described on EPA/NADCA websites (I apologize for my simplistic terms). Both said they would use Fosters 40-20 on all insulated areas - the first company said they would fog with Fosters 40-80 into clean ducts.

    What is a good course of action? What additional questions should I be asking? Is cleaning of ducts necessary?

    Thanks for any advice that can be offered!

    Catherine in New Orleans

  2. #2
    Join Date
    Nov 2000
    Waco, Texas, USA
    Your house is too cold. Raise the stat a couple degrees.
    "And remember my sentimental friend......that a heart is not judged by how much you love, but by how much you are loved by others" - Wizard of Oz.

  3. #3
    Join Date
    Jun 2003
    Madison, WI/Cape Coral, FL
    Grills/ducts are that are wet for more than a couple days grow mold. You live in wet climate. Get %RH meter and track the temperature and %RH. High indoor %RH allows the grills to sweat during the off cycle of the a/c. Less than 50%RH inside decreases the amount of condensate on the grill. Operating your fan in the "on" mode also helps dry the ducts/grill during the none-a/c time. Drying the coil/ducts with the fan unfortunately raises the indoor humidity levels above 50%RH.
    One of the solutions to this problem requires a whole house dehumidifier connected to the a/c ducts. The unit circulates dry air throughout the home via the a/c ducts when the home or ducts are wet. Keeping the home <50%RH is very comfortable and allows a warmer indoor air temperature.

    This an example of the equipment available.
    Several models are avialable from many manufactures.

  4. #4
    Join Date
    Jul 2004
    New Orleans

    mold on grills

    I know this may be a silly question, but what is a %RH meter? Also, why would Steve say my house is too cold - I would think that 80 degrees in a humid climate might be too warm.

    Thanks for the info.


  5. #5
    Join Date
    Jun 2004
    Earth, 20th century, North America, Texas. HVAC tech in late 70s.
    %RH is for "percentage of Relative Humidity", a measurement of air humidity. You can get one at stores like Walmart, it's called hygrometer. It usually measures both temperature and humidity. It's around $20 for a cheapo version.

  6. #6
    Join Date
    Apr 2002
    If your grills are painted, discard them and replace with new ones with a factory finish. Do not paint with Latex paint.

    Gone on vacation for a week and temps set at 80 degrees in a humid climate. Without A/C you had no dehumidification so mold grew on painted grills or dirt on the grills.

    I believe another failure will be discovered. You will have a large opening in the duct system somewhere . . . possibly at the location where the UV light was installed.

    You're fortunate to have rigid ducts, they are easily cleanable.

    Good luck,

  7. #7
    Remove some of your grilles and look inside of the attached ductwork. If the mold/mildew problem is only on the grilles then cleaning the ducts is not the solution. Mildew growth on the grilles is usually caused from condensation on those grilles. There are several factors that can cause condensation on the grilles and you should be looking for the cause of the condensation problem. Be sure that whoever looks at your system can explain to you what is causing the problem so that you understand exactly what you are dealing with. If they cannot explain properly then keep searching until you find someone who can. BB

  8. #8
    Join Date
    Mar 2004
    Just a thought, like was said air too cold. Like maybe because of a plugged up filter or dirty coil and not moving enough air? or what if the duct is not insulated very well, could it be sweating?

  9. #9
    Join Date
    Nov 2004
    Duct cleaning is not helpful in this situation, or any other for thst mstter, least of all a condensation problem. "Air too cold" makes me scratch my head since we are talking about a/c. Lowering RH is the answer, and the causes can be many. Ask for referrals to a reputable hvac contractor to find the solution. Good luck.

  10. #10
    I have a similar situation mold on paited grills and on painted ceilings near air handling unit. Ducts were cleaned and grills replaced. This has made everything great for now until summer comes again. I think the moisture is coming from the ducts sweating, will insulating the ducts correct this problem ???

  11. #11
    Join Date
    Jun 2003
    Jacksonville, FL.

    Does your furnace have a variable speed motor? If so, all that may be needed is a little caulk.

    I recommend sealing the gap that MAY exist between the boot of the register & the ceiling. Just an idea that's worked for me in the past....

  12. #12
    Join Date
    Jul 2003
    Did you find a R.H. / Temp. meter at Walmart or HomeDepot? I have one located next to my clock in the bedroom, This way I check at least twice each day. Teddy bear has many post on this subject, you can do a search to find other post too.

  13. #13
    Join Date
    Dec 2004
    springfield Illinois
    Mold is ALIVE it wont just go away mold produces spores. so small that only static electric filters of true hepas can catch them. MILLIONS OF SPORES EVERYWHERE. Mold needs only two things to live water and food allow me to give examples of each:
    water: there are up to 110 grains of moisture of water in one pound of 70 degree air (thats a lot when your a spore of mold millionths of an inch in size)infinite. it gets higher the warmer you go (warm air is more humid typicallly.

    food:dead skin cells, pollen, dander, drywall dust, smoke reside, oils, fabric particles, ANYTHING that can and does biodegrade is food for mold. these things are so common i duct work and on every surface of your house.

    MOOLD CAN KILL new research says that childern with developing lungs 0-14 years that are exposed to certain strains of mold are 120 times more likely to have ashsma and allergies.(do the reaseach your self you dont belive me)

    THERE IS HOPE we have to do three things at this point get the spores out or dead , kill the living mold and keep it from coming back

    Mold has enimies

    what kind of furnace ie: where is the filter
    which way is air flow
    how manny btus of approxamate size of ducts supply and return
    size of the house
    geographical location so important for humidity
    kind of house basment,slab,crawl,
    are the grilles painted
    where are the grilles located floor walls cellings

    How adiment you are about keeping this problem from happening again

    How much are you willing to pay to fix it

    Please dont be freaked out im not trying to scare you into duct cleaning i just want you to realize that mold can be a VERY SERIOUS PROBLEM thankyou

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