If your HVAC system has been running for a while, it could be hiding an unwanted guest—mold. Mold thrives in damp, dark spaces, making air ducts the perfect breeding ground.

Left unchecked, mold in your air ducts can lower indoor air quality and negatively impact your health. But how do you know if it’s there?

Here are the top 4 signs to look for and what you can do if you spot them.

1. Musty or Unpleasant Odors

A constant musty smell, especially when your HVAC system is on, is often the first sign of mold in your ductwork.

Since we get used to indoor smells over time, pay attention when you walk into your home after being outside. A stale, moldy odor could be a red flag.

What to do:

• Turn off your HVAC system to prevent spreading mold.
• Schedule a professional duct inspection and cleaning.
• Use a dehumidifier to reduce indoor moisture.

2. Visible Mold or Discoloration Around Vents

Look closely at your air vents and registers. Do you see black, green, brown, or yellowish spots? That could be visible mold.

Mold spores spread easily through your HVAC system, so even small growths shouldn’t be ignored.

What to do:

• Use a flashlight to check inside vents.
• Don’t clean visible mold with household products—it can spread spores.
• Call a professional duct cleaning service for proper mold removal.

3. Moisture or Water Droplets Around Vents

Condensation or water around your vents is a sign of excess moisture—and that’s exactly what mold loves.

If you see damp spots or droplets, your system could be contributing to mold growth.

What to do:

• Fix any leaks or condensation issues in your HVAC system.
• Keep humidity below 50% with a dehumidifier.
• Improve airflow and ventilation in damp areas.

4. Allergy Symptoms or Breathing Issues

If you or your family members experience sneezing, coughing, itchy eyes, or congestion—especially when the HVAC is on—it could be mold-related.

You may feel better when you leave the house, which is another clue that something in your indoor air (like mold) is to blame.

What to do:

• Track when symptoms get worse—if it’s when HVAC runs, mold may be the cause.
• Get an indoor air quality test.
• Consider using an air purifier with a HEPA filter.

How to Prevent Mold in Air Ducts

Preventing mold is easier than dealing with it. Here are a few simple but effective tips:

• Change Air Filters Regularly – Replace every 1–3 months.
• Keep Humidity Levels Low – Use a dehumidifier and ventilate your home.
• Schedule HVAC Maintenance – At least once a year.
• Clean Ducts Periodically – Professional cleaning helps eliminate spores early.

In a Nutshell

Mold in your air ducts isn’t just gross—it can seriously affect your health and indoor air quality.

If you notice any of the signs above, take action quickly. Professional duct cleaning is the safest and most effective way to remove mold and keep your HVAC system in top shape.

FAQs

Q1. Can I remove mold from my air ducts myself?

Not recommended. DIY methods can spread spores and may not fully remove the mold. Professionals use specialized tools and EPA-approved disinfectants.

Q2. How often should I clean my air ducts to prevent mold?

Generally every 2–3 years. But if you live in a humid climate or notice mold signs, more frequent cleanings are a good idea.

Q3. Can mold in air ducts make me sick?

Yes. Mold spores can cause allergic reactions, asthma flare-ups, and other respiratory issues—especially for those with weakened immune systems.