How To Stop Condensation On Ductwork

When you inspect your HVAC system, check for condensation, or moisture, around ductwork. Occasional drip is normal and commonly isn't an issue. However, constant dripping causes paddles around the ducts, which could lead to mold growth and structural damage, so it is essential to fix this as quickly as possible. Fix condensation around ductwork by following these tips.

Check Temperature

To fix condensation on ducts, gather:

  • work gloves
  • step-ladder
  • flashlight
  • thermometer
  • Phillips screwdriver (optional)
  • metallic foil tape (optional)
  • caulk (optional)
  • paintbrush (optional)
  • insulation

Temperature differences between the exterior temperature and ducts commonly cause moisture  Check the thermometer, or hold one in the room if one is not already installed. Hold the thermometer near the ductwork to check the temperature. 

Increase the thermostat temperature by one to five degrees until you get a balance and moisture disappears. Increasing the duct temperature helps reduce the risk of moisture because when the warmer air meets the cooler duct air, it cools and causes the moisture.

Adjust and Insulate Ducts 

Blocked air vents prohibit air flow, which causes the inside of the duct to cool. Inspect all air ducts to ensure they are fully open and not blocked. 

Whenever possible, leave basement doors open to the upper level to balance temperatures. The ductwork should also be spaced apart enough to allow air flow. 

To increase temperature further, add another layer of insulation. The inner layer of insulation is made from foam and the outer layer made from foil. Wrap the insulation around the duct, and secure it with duct tape.

Run your hands along all the ductwork to feel for leaks, using a flashlight. Seal leaks with a special foal tape designed for duct work.


If you have crawl space ducts, consider placing a cover over the dirt and remove exhaust fans to reduce humidity. Since crawl spaces are normally cooler, a dew point more than the duct temperature makes the area more humid. 

Run a dehumidifier in the basement until no more moisture is present, emptying the reservoir as needed. After moisture has decreased, run the dehumidifier normally.

Caulk Ceiling Ducts

Set a step-ladder to reach the ceiling duct with the most moisture. Use a Phillips screwdriver to detach the two screws, holding one hand on the vent, and lay part aside. 

Coat the brush with caulk, and brush on a 1/8 to 1/16 layer on all corners of the grille. Be certain to cover the unexposed area of the ceiling where the grille connects. Let the cure twenty-four hours, then reinstall the vent.

If you find that you are unable to stop the condensation on your ductwork, you may need professional assistance. Contact a contractor who offers air conditioning services to have them inspect your system.