9 Types of Molds That Can Be Found in Your Ducts

Many property owners don’t think twice about their air ducts until they notice an odd musty smell. The cause of this odour likely stems from unchecked mold growth, a dangerous issue that can affect your air quality and even your health. Let’s go over the most common types of molds found in your ductwork and the best way to address them.

How Does Mold Grow in Your Ductwork in the First Place?

Mold spores from the outdoors can easily find their way into your HVAC system. When these spores come in contact with condensation, they can quickly reproduce and spread through the air ducts. In addition to condensation, other factors like dirt and dust buildup can create the optimal environment for mold growth.

Since air ducts lie hidden behind walls and ceilings, it’s easy to forget about potential mold growth until the smell becomes noticeable. That’s why scheduling regular deep cleaning services is so important, as it can help you identify and address this issue before it gets out of hand.

9 Common Types of Mold in Air Vents

Mold comes in all shapes and sizes, but some species thrive in HVAC systems more than others. Here are nine of the most common types of molds you may find in your ductwork:


Acremonium is a type of mold with a white, powdery appearance. While it grows very slowly, it releases dangerous toxins into the air. Acremonium can spread throughout your HVAC system and cause serious health issues when left unchecked.


Stachybotrys is one of the most hazardous types of mold, and it’s easily recognizable because of its black colour. It produces mycotoxins, which are very dangerous when inhaled. If you spot this black mold in your HVAC system, call a professional immediately.


Alternaria is a common fungus with a velvety black, gray, or green appearance. Since it thrives in places with constant running water, you might have HVAC damage if you find it in your ductwork. Be sure to call a professional to address this problem immediately.


Chaetomium is a cotton-like mold with a brownish hue. Its color can change when it reaches different growth stages, so it can be hard to identify. Chaetomium tends to grow in walls, but some can find their way into air vents. 


It can be challenging to distinguish Aspergillus from other types of mold, and it’s one of the most common species found in air ducts. This fungus comes in various colors— green, white, brown, or black—and is known to cause allergic reactions.


Fusarium has a pale rose, burgundy to bluish-violet appearance depending on its growing conditions and species. It mainly grows on surfaces with water damage, so look for leaks if you see this mold in your HVAC system.


Trichoderma is a mold with a greenish-gray or yellow appearance. It usually grows on wet surfaces and can spread quickly in the presence of moisture. If left unchecked, Trichoderma can cause severe respiratory issues.


Mucor has a grayish-brown color, and it tends to form cottony masses. It’s also known as the “bread mold” because it often grows on bread products but can also thrive in your air conditioners and vents.


Ulocladium is a type of mold that looks like layers of black dust. While much rarer than the previous molds we mentioned, Ulocladium is one of the most difficult to eliminate once it’s in your ductwork.

Easy Ways to Tell You Have Mold in Your Air Ducts

You don’t have to climb inside your ductwork to check for mold. Watch out for these warning signs and contact a professional the moment you notice them:

  • Off smells. Do your vents emit a strange, musty odor? The smell will only worsen over time, so it’s important to act quickly.
  • Unexplained allergic reactions. When people on your property experience runny noses or itchy eyes and throats, it could be due to mold in your air ducts.
  • Discoloration on walls and ceiling. Look for dark spots or any unusual patches on your walls and ceiling. These can be signs of mold growth, so have a professional check them out right away.
  • Excessive humidity. Do your indoor spaces feel uncomfortably clammy? Too much moisture in the air leads to mold growth in the long run, so try to reduce humidity levels as soon as possible.
  • Dirty vents. Check your air vents for any dust or grime buildup. Since dirty environments can significantly increase the chances of mold growth, you likely already have some growing in your ductwork.
  • Visible growths. Once the mold completely takes over your HVAC system, it will be impossible to miss. The areas in your property exposed to frequent moisture (bathrooms, kitchens, basements) are more prone to mold growth, so inspect these places thoroughly.

Why You Need to Address Mold Growth ASAP

Mold doesn’t just cause mild allergic reactions. Many species produce mycotoxins, carcinogens, and other harmful substances that can negatively impact your health. Some symptoms include:

  • Headaches and dizziness. The presence of mycotoxins in the air can make you feel disoriented or nauseous.
  • Respiratory issues. Mold can trigger asthma attacks, bronchitis, and other breathing problems.
  • Infections and chronic fatigue. If not treated quickly, mold growth can lead to lasting infections or even death in extreme cases. Long-term exposure will also make you feel lethargic or unmotivated.

It’s clear that mold is a major health hazard, so don’t delay in dealing with it. And don’t try to fix the issue yourself since it requires special cleaning solutions and safety protocols.

We hope that knowing the common types of molds and their signs will help you quickly identify and address them. We at Brilho Luxury Home Services Inc. offer comprehensive duct and ventilation cleaning services to keep your property safe and healthy. Call our experts at 416-923-3300 or email [email protected] to learn more about our service and schedule an appointment with us today. We guarantee exceptional results.