How do I stop condensation from A/C ductwork vents?

I have condensation dripping out of my ceiling A/C vents and soaking the ceiling plaster. Probable cause is insufficient insulation/temperature difference. Can I remove the vent cover and spray foam insulation around the ductwork to mitigate the problem?

  7 answers
  • Laura Cooper Laura Cooper on Sep 13, 2018

    Hi Jeannie, I work in HVAC. First off, you are right about the lack of insulation. Condensation only forms where cold and warm air meet. Removing the register cover, however, will not give you access to the ductwork. You will need to place insulation around the duct by going up into your attic. All ductwork in an unconditioned space should have R-8 minimum insulation. The least expensive solution for this would be to place fiberglass insulation around the ducts in the attic. Be sure to use tape on all the seams. While I love spray foam insulation, this is not the best application for it.

    • See 1 previous
    • Laura Cooper Laura Cooper on Sep 15, 2018

      Yuck! I know what you mean! But in the end it will be worth it because more cooling will make it in your house instead of the attic which should also lower your energy bill. An hour of misery will yield a big return. 😉

  • Kelli L. Milligan Kelli L. Milligan on Sep 13, 2018

    Not sure, but that is sure worth a try. Try to get behind it so to insulate from the outside wall.

  • William William on Sep 13, 2018

    Duct needs to be wrapped with insulation. Spray foam around the duct won't do much. You may actually create a dam where moisture can build up.

  • Eloise Eloise on Sep 14, 2018

    Check out the videos on YouTube to see if any address your specific issue:

  • Nori Estrada-Garriga Nori Estrada-Garriga on Sep 14, 2018

    We have the same issue in our finished basement. Our solution was to place dehumidifier in the furnace room.

  • Jan Clark Jan Clark on Sep 14, 2018

    Once you fix the obvious problem, don't forget the other one! Your ceiling has been soaked! If it is not misshapen, it needs to be treated with a product like Kilz to prevent mold/mildew before you repair and repaint. : )

  • Phyllis Wolper Phyllis Wolper on Sep 14, 2018

    In North Texas, condensation around HVAC air ducts is caused by dirty filters. Try changing the filters more often if you have pets that shed, or live in an area where you have excessive dust, or when you've done remodeling.