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A/C Troubleshooting: Why Are My Air Ducts Sweating?

Summer is the time of year when your air conditioning unit has to work the hardest to cool your home. On hot days you may notice water droplets forming on your visible air ducts and wonder whether this is normal. What you see is condensation, also known as ductwork sweating. It does not necessarily mean that your A/C system is in trouble, but it may still be something that requires your attention.

air ducts sweating

What causes duct condensation?

As the humidity level rises outdoors, condensation will gradually begin to form on the surface of your air conditioning ducts. The colder the air is inside the duct, the greater the chance of ductwork sweating. It’s a natural process, and similar to the way a chilled soda begins to sweat once you take it out of the refrigerator on a hot day.

However, ductwork sweating can also be caused — or exacerbated — by the following factors:

  • Poor insulation.
  • Excessive moisture in the air.
  • Dirty air filters.
  • Blocked ducts.

In come cases, duct condensation can be a sign of a duct leaking air, which reduces your A/C unit's efficiency. If you own an older home or your ductwork is not properly maintained, ductwork sweating is more likely to become an issue as both the temperature and humidity levels rise.

When should I worry about condensation on A/C ducts?

Occasional condensation on A/C ducts is not a problem, but keeping an eye on the situation is recommended. Persistent ductwork sweating may eventually lead to water damage. Excessive condensation can also create conditions favorable to mold or mildew forming in areas surrounding the duct itself. Individuals suffering from asthma and allergies may experience more severe symptoms should mold and mildew establish themselves and then spread to other parts of your home.

What can I do about ductwork sweating?

To avoid duct condensation and duct leaking, choose flexible, fiberglass and insulated materials rather than metal. If you do have metal ducts, check to make sure they are properly wrapped with fiberglass insulation. While a good fit is needed, insulation that is wrapped too tightly will be less effective at reducing ductwork sweating.

You can also take the following steps to avoid excessive duct condensation.

  • Reduce the humidity level around your air ducts. Keep ducts spaced apart so air can flow between them. If ducts are located in a crawlspace underneath your house, cover the soil to reduce moisture. If they are located in your attic, be sure the area is properly insulated and any cracks or holes are sealed. If you live in a consistently humid climate, a dehumidifier can help keep the air around your ductwork dry.
  • Unblock any ducts that are restricting air flow and have them cleaned regularly. When air cannot circulate freely throughout your A/C system, it will become colder inside certain ducts, increasing the likelihood of ductwork sweating.
  • Keep your air filters clean and change them regularly. Replacing filters every one to three months is recommended, but you can also simply follow the instructions that come with the air filter you purchase. If you own pets or someone in your home has a dust allergy, you may need to change the filter more often.
  • Repair leaking ducts. The more cold air that seeps out, the more condensation will form. You can detect a leaking duct by using a pressure gauge or simply placing your hand on the duct to feel for air escaping. 

How can I tell whether my A/C unit needs to be repaired?

If you are experiencing any of the following, it may be time to have an HVAC professional diagnose the cause of your ductwork sweating and fix the problem.

  • Reduced airflow can be a sign that your A/C compressor is no longer working as it should. If replacing the indoor air filter does not improve the situation, the compressor may need attention.
  • noisy A/C system may indicate the presence of a broken fan inside the unit.
  • A sudden increase in condensation on the exterior of the A/C unit can signal an internal temperature issue or a pressure leak. 
  • Inconsistent temperatures inside your home, such as cold and warm zones on the same floor, may indicate a problem with the A/C unit or the ductwork. 
  • Foul odors coming through your air vents could be an indication that the A/C unit needs professional cleaning and maintenance, especially if you have not been changing the filter on a regular basis.
  • Larger electric bills than in previous years, especially during the summer months, may also be a sign that your A/C unit is struggling to keep your home cool — even if ductwork sweating and duct leaks are not obvious. In this situation, a professional inspection and energy audit can help you determine whether the unit is still functioning efficiently.

If your air conditioner is not performing as well as it once did, American Home Shield can help. Our network of professional contractors offer courteous assistance with several types of A/C repairs that are covered through our home warranty program.

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