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What Causes Condensation on Air Ducts?



The two most common causes of condensation in air ducts are too much moisture in the air and the effect of inadequate ductwork. When water condenses and drips on the air ducts in your home or business, it causes health issues. The water that drips off your ducts and onto insulation, can cause the insulation to compress, which decreases it’s ability to insulate the R-value and also cause your drywall, ceiling or cooling to leak and start the growth of unhealthy mold.


The impact of too much moisture in the air near your attic, ductwork or crawlspaces means you may run the risk of condensation to form. The average humidity levels, can also increase this problem, based on the outdoor weather conditions, which causes condensation levels to rise when it’s hot outside.

The effect of inadequate insulation on duct work, will also cause condensation. If you have the proper amounts of insulation duct work, then condensation will not form. You must make sure that your duct work is properly insulated, to avoid this problem.

Shopping for the right HVAC company to help you with the challenges of improper or no insulation of ducts, sealing crawlspaces, dehumidifier disparities, and air flow, can be daunting. Make sure that you add insulation in batts or proper HVAC tape, to make sure that you reduce the R-value. You must also remember that you cannot have the wrappings too tight. The service company will ensure that your ducts has no gaps for at least two-inches to effectively- illuminate condensation, and also make sure you use HVAC tape to seal joints between the duct segments.


The most common cause of moisture in the air, when dealing with condensation is caused by inadequate ventilation in your attic or crawlspace. You will need to make sure that your ducts has vents to work properly. Today, vapor barriers wrap are recommended to decrease the moisture absorption into the air.

One of the main reasons for condensation on air conditioning ductwork, is that if the temperatures reach high levels during the summer, proper ventilation is key. Some new air condition systems make the air inside the ducts cooler. Dirty filters also restrict air flow, so make sure your filters- stay clean and use vapor barriers for clean air ducts.


When a new system is installed, the pipes in your attic or duct spaces, must be sealed properly. If there is a small opening, it allows warm to come in with the cool ducts, which can cause condensation. There are also other reasons for excessive moisture in your crawlspace:


  • You may need to add fan venting- which has a humidistat humidifier setting

  • You will need at least one square foot of the vent area for every 150 square feet of space

  • There is no plastic ground cover

  • Inadequate cross ventilation

  • Leaky ductwork


Essentially, when the air is cooled, the air can only hold so much moisture due to the dew points, and the air conditioning must remove humidity and moisture. If it is unable to do so, moisture comes out and will cause condensation.

In the winter time, if the outside temperatures drop down below 40 degrees, condensation will start forming, which cause drips and moisture. You must make sure the air ducts are insulated to code and metal registers are all low e-wrapped. You can also have an automatic system installed, which use a zone controller, which has an input for a carbon monoxide sensor. This feature allows the automation detection of the Co HVAC fan to circulate fresh air at all times. The use of this type of system, is widely used these days to avoid major condensation.

There are several things that you can do to prevent condensation of your ductwork. Some people use the bathroom exhaust fan, and make sure that their doors and windows are sealed when they take a shower, insulate cold air supply ducts, or wrap cold water plumbing pipes to reduce moisture throughout your home or business. Make sure that the professional service company that you use schedule maintenance visits, seal the system, and remove bacteria.

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