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By Tom Moor
Air ducts and vent
Posted 9/6/23

Just like water droplets form on a cold glass of iced tea during a hot summer’s day, condensation can also form on your air ducts when the warm air inside your home contacts the cold air ducts. In serious cases that are left untreated, condensation on ductwork can lead to expensive repair issues.

Keep reading as, your trusted advisor for all things HVAC-related, discusses common causes of sweaty air ducts and how to prevent this issue.

Can Condensation Damage Ductwork?

A small amount of duct sweating typically won’t cause harm; however, excessive condensation can damage your ductwork. The most common problems caused by ductwork condensation include corrosion, duct material degradation, reduced effectiveness, leakage, and mold and mildew growth. It’s imperative to contact a reputable HVAC technician to inspect the ductwork and make the appropriate fix before further damage occurs.

“When it’s hot and humid, there’s going to be condensation on the registers and the ductwork,” said Jessica Wicks, President of DUCTZ, a national provider of commercial and residential air duct cleaning and HVAC restoration services. “If you can locate the problem, it could be as simple as replacing the air filter or insulating the ductwork. But when it’s dripping, that’s problematic, and it could lead to microbial growth.”

8 Common Causes of Sweaty Air Ducts

1. Temperature Differential

The most common cause of condensation on air ducts is a significant difference in temperature between the air inside the ducts and the surrounding environment. When warm, humid air from your living space contacts the cooler duct surface, condensation can form.

2. High Humidity Levels

High indoor humidity levels can also increase the likelihood of condensation on ductwork. When the relative humidity inside is elevated, the air contains more moisture, causing it to condense when it reaches the cold duct surface.

3. Inadequate Insulation

Poorly insulated or uninsulated ducts can be prone to condensation. Insulating ducts helps maintain a consistent temperature, reducing the likelihood of condensation forming on their surfaces.

“We always recommend insulating all or part of the outside of the ductwork, especially in unconditioned spaces,” Wicks said. “This will protect against condensation and increase the efficiency of your HVAC system.”

4. Air Leaks

Air leaks in the ductwork can bring in warm, moist air from surrounding areas. When this air comes into contact with the cooler ducts, condensation may occur. Professional duct sealing services can prevent this issue.

5. Duct Location

Ducts located in areas with significant temperature variations, such as crawlspaces or unconditioned basements, are more susceptible to condensation. These areas tend to have cooler temperatures, making ducts vulnerable to condensation.

6. Poor Ventilation

Inadequate ventilation in areas where ducts are located can contribute to condensation. Proper ventilation helps maintain a balanced temperature and humidity level.

7. Insufficient Airflow

In some cases, inadequate airflow within the ducts can lead to condensation. Reduced airflow may result from blocked or dirty filters, closed dampers, or improperly sized ducts.

8. Type of Ductwork and Installation

The type of air ducts and the installation process can also greatly affect whether condensation forms.

“Some condensation is common with metal ducts, but flexible ducts can also experience sweating if the connection points between them are not adequately sealed,” said Jeff Gervais, CEO of Gervais Mechanical in Auburn, MA. “This can lead to leaky ducts, resulting in fogging. Improper installation of the entire system can contribute to the same problem. If your ducts aren’t hung properly or are in contact with each other, they can create cold spots at the joints where condensation can also form.”

How to Prevent Condensation on Ductwork

To avoid the consequences associated with sweaty ductwork, consider the following tips:

The Cost to Repair Ductwork

According to, duct repair can cost between $500 and $2,000 on average. Some of the factors that affect the cost include the extent of the damage, accessibility of the ductwork, the type of ductwork, and local labor and contractor rates.