Asked on Nov 02, 2013

Sweating AC vent

Bluegrass B
by Bluegrass B
We have an AC vent in the upstairs master bath toilet area that is sweating and starting to grow mold. It has reoccurred since a whole house remodel in 2011, at that time the drywall, vent, lighting, and fan (which is vented through the roof) were all replaced. The mold is occurring where the vent is caulked to the ceiling. We have another upstairs bath & have not had the same issue. No other vents in the house sweat. We live in FL, keep the AC set on 72 upstairs which allows the temp to stay around 78 in the bathroom area. We had to replace the light in the ceiling since the remodel due to the moisture & mold starting to grown on the light housing. The AC company says this just happens sometimes and has offered no solutions other than to turn the vent so the cold air doesn't blow on the hot light fixture, the lights are LED which should not even be getting hot. Any suggestions would be greatly appreciated.
  5 answers
  • Patricia W Patricia W on Nov 03, 2013
    Did the company give you a warranty?
  • Well the answer is you have a nice cold condensing surface which is meeting up with humid enough air allowing for condensation to form. While this could be caused by air-leakage from the outside and that is worth checking, my first question is do you run the bathroom fan while you are taking a shower & for at least 15 minutes afterwards? If not I would clean those areas, install one & do so? Whether you do or not for the prior, my next question is are you sure it vents outside the house/attic to the exterior as many don't & then you would need to fix that.
  • Leo9585 Leo9585 on Nov 03, 2013
    we have recently had a customer with a similar issue and unfortunately they had a water leak from upstairs. You may want to check for that. It's amazing how a small,leak can travel over pipes and wires and come out in places you would never expect. When you have a bathroom upstairs your leak is not always obvious upstairs.
  • James Bryan C James Bryan C on Nov 04, 2013
    I lived in Florida for most of my life.. when you have a situation like this the most likely culprit is your vent fan exhaust does not vent to the outside. Most likely the builder or installer vented the moist air to your attic and this it the problem you are facing.. check in your attic near the ac duct work fin the exhaust fan vent and either vent it outside or move it from close proximity of any ac duct.. use vinegar to kill the mold 5% straight in a small spray bottle will do the trick
  • Bijan Air Conditioning Bijan Air Conditioning on Nov 05, 2013
    you need to put more insulation around that went from the top of ceiling .
    • Jay Taylor Jay Taylor on Jul 28, 2014
      @Bijan Air Conditioning I think, it is probably because of too much humidity in the house. Ducts sweat because the outside surfaces of the ducts are below the dew point of the air in ... If the source of the water is strictly on the outside of the duct, you can stop the sweating by insulating the duct. Note that sweating ducts has nothing to do with moisture in the air inside the ducts.