Updated May 18th, 2025
Condensation or sweating is a common problem with air conditioner ducts. Long term condensation leads to various issues with your AC system.
Condensation can frequently be seen as water drops collecting on the outside of AC ducts and vent openings. It can also form small water pools on the floor in severe cases.
What Causes Condensation in HVAC Ducts?
Main causes for condensation occurring in your AC ducts include the temperature difference between the outside air and AC vent, improperly sealed AC ducts, and lack of insulation around these ducts.
However, ductwork sweating can also be aggravated by factors like
- Too much air moisture
- Dirty air filters
- Clogged ducts
Why Is Water Dripping from My Ductwork?
Condensate drain problems cause water to drip from your AC’s ductwork. The function of the condensate drain system is to collect moisture removed from the air and dispose it into a drain. Water leakage can be caused if
- the condensate tube is clogged with dirt, algae, or minerals
- the drip tray is leaking
- the evaporator coil, which freezes on scorching days, starts to thaw
Also read: How to Eliminate Mold from Air Conditioner Duct
Can Too Much Insulation Cause Condensation?
Sometimes extreme insulation can cause condensation. This is because insulation warms the indoor area of your building. Generally, warm air holds more moisture and makes the inside of your building more humid. However, temperature changes allow the building to become cooler in the evening. This prompts the air inside to cool down and release moisture, which results in condensation.
Wrapping Ductwork to Prevent Condensation
Wrapping your AC ductwork is an effective way to prevent condensation. Duct wrap has a foam insulation inner layer and a foil outer layer. Cleanly wrap it around the AC duct and fasten with duct tape near the joints.
Also read: 6 Most Common HVAC Duct Problems You Should Know About
How Do I Stop Condensation on My Air Conditioner?
Here are some tricks to stop condensation on air ducts:
- Instead of metal, choose fiberglass or other insulating materials for your ductwork. In case you have metal ducts, make sure they are appropriately wrapped with fiberglass insulation.
- Try to reduce the humidity level in the air near the air ducts. You can go for a dehumidifier if that helps to reduce the condensation.
- Unblock any ducts that are restricting airflow and have them cleaned regularly.
- Regularly clean your air filters and change them once every three months.
- Repair leaking ducts as early as possible.
Why Ducts “Sweat”
When warm, humid air passes over cold duct surfaces below the dew point, moisture forms and drips. This commonly happens in unconditioned spaces like attics or crawl spaces where insulation or sealing is insufficient.
Upgrade & Repair Insulation
- Inspect existing duct wrap for tears or compression and repair with foil-faced tape or mastic.
- Add high-R insulation (R-8 to R-11) on exposed ducts to keep metal above the dew point.
Seal All Joints & Seams
Air leaks let conditioned air escape into warm, humid areas. Seal seams, joints, and penetrations with mastic or UL-approved foil tape to create an airtight barrier.
Control Indoor Humidity
- Maintain 30–50% relative humidity using whole-house or portable dehumidifiers.
- Run exhaust fans in bathrooms and kitchens and ensure laundry vents exhaust outdoors.
Condition the Surrounding Space
Insulate attic floors or crawl-space ceilings and install a vapor barrier over exposed soil to lower ambient humidity and temperature swings around duct runs.
Ensure Proper Airflow & Spacing
- Keep at least 1–2 inches of clearance around each duct so air can circulate and insulation can perform properly.
- Close and seal dampers on unused zones during cooling season to prevent humid air infiltration.
Add Thermal Breaks or Vapor Retarders
Apply closed-cell foam or specialized vapor-retarder coatings on duct surfaces to block moisture migration through the metal and insulation.
Use Mechanical Dehumidification & UV Treatment
- Integrate a whole-house dehumidifier into your HVAC to lower the indoor dew point and protect all ductwork.
- Install UV-C lights in the return plenum to inhibit mold or microbial growth on coils and duct walls.
Professional Inspection & Testing
Have an HVAC technician perform a thermal imaging scan to identify cold spots, verify insulation effectiveness, and pinpoint areas at risk of condensation. Regular inspections ensure long-term prevention.
White Mechanical, Inc.
Founded in 2002, White Mechanical, Inc. in Laguna Hills, CA, is one of the most trusted and licensed (HVAC) service providers, proudly serving Orange County and the surrounding communities. Our management team has more than 28 years of experience in various aspects of HVAC technology. All our HVAC technicians are professionally skilled and certified to deliver outstanding residential HVAC services as well as commercial HVAC services to our clients. We offer professional HVAC services including installation, maintenance, air conditioning repair, and more at very reasonable prices.
