Mold in Air Ducts: Removal and Prevention in Residential Homes

Every year, millions of homeowners are plagued by respiratory systems ranging from mild to severe. Pollen and poor air quality can affect you outdoors, but your HVAC system can cause problems inside your home. That’s often due to mold, which can grow in a variety of locations under the right conditions, including air ducts.

In this guide, we’re going to talk more about mold and why heating and air systems are prime candidates for these harmful spores. We are also going to tell you how to prevent mold from growing in your ducts and discuss the remediation options available to homeowners today.

How Mold Forms in Air Ducts

Have you ever opened up a loaf of bread only to find a green spot of mold growing on a piece? Mold isn’t picky and can grow on a variety of surfaces both organic and inorganic. That said, as air ducts are made from metal and synthetic materials, for mold to grow there two things have to be present – moisture and heat.

If moisture accumulates inside your ductwork, mold can begin to form a colony given the right conditions. These spores can cling to a variety of things to use as fuel including dust, which can help them spread quickly with a bit of heat. Mold can grow on the inside of air ducts or the outside poorly insulated ones from excess condensation.

Bare metal trunk and distribution air ducts are susceptible to mold, but so are other parts of an HVAC system. Wall stacks, elbows, and boots are all areas that can experience mold as well, although the ductwork on an HVAC system itself is typically the biggest area of concern.

How Can I Tell if Mold is in My Air Ducts?

One of the problems with mold is the fact it’s sneaky and has the ability to spring up in unlikely places that tend to be hard to reach. That includes corners and crevices of air ducts which aren’t something easy to see.

The easiest way to detect mold around your HVAC or air ducts is to simply look for it. If you see mold around the vent covers or grates, you know you have an issue on hand. Even if you can’t see visible mold on the walls around vents in your home, spots on the grill could indicate an underlying problem. If that’s the case you’ll want to give all the vents in your home a further inspection.

Do you get a musty smell when you turn on your air conditioner? That’s another sign that mold could be present in your system. It can take a considerable amount of mold growth to provide that smell, however, and by that time spores have already penetrated your home. When the AC is off, you may never notice the smell, but a furnace can cause just as many problems.

If you experience aggravated allergies, itchy eyes, and other respiratory problems with your system running, you could have mold in your ductwork. If no visible mold is present, but aren’t quite ready to call in a professional to assess the situation, you can try mold test kits, although they can vary considerably when it comes to accuracy.

Removing Mold from Air Ducts

When you’ve got a mold issue, whether large or small, the next step is an obvious one. The mold needs to be removed from the affected areas, but you’ll want to take a few things into account before attempting to take on the job yourself.

DIY Mold Removal

Surface mold on the outside of ducts or registers can be easily cleaned provided you follow a few simple rules. We recommend wearing a respirator, not a face mask similar to what people wear in public with Covid-19. Mold particulates are very fine, and as reactions to the spores can be delayed, it’s better to be safe than risk an allergic reaction.

For that reason, we only recommend using a half-mask respirator similar to what’s used in paint booths and for paint removal. This model from 3M is rated or mold is ideal with P100 filters and stays comfortable on the face during extended usage. No matter how small the spot of mold is, eye and hand protection are also important so you’ll need gloves like these from Ansell and “splash proof” goggles without holes.

The last type of personal protection you’ll want to consider may be overkill for a small scrub, but something you’ll see professionals use. A high-quality Tyvek suit can cover your clothes and keep mold spores from getting into the fibers and come in a variety of sizes. As for the chemicals, well that varies depending on the type of problem you have.

For things like vents and surfaces that need a quick, but thorough cleaning, a solution like RMR-86 or Concrobium will work and are commonly used on a variety of surfaces. Products like Shockwave are a step up and often used by professionals.  This video will give you an idea of what to expect with smaller items like vents.

While it may only cost between $65-$120 to handle a small external issue, when mold is inside ductwork or covers areas large than 10 square feet, you’ll want to call in a professional mold remediator. If you do think you can tackle the issue on your own, you can read a bit more about the types of mold found in vents and cleaning in this guide.


Estimated Cost

Respirator Mask


Safety Goggles




Tyvek Suit


Cleaning Solution


Professional Mold Removal Services

When you know you have mold within your air ducts, it’s time to call in an HVAC professional to assess the situation. Unfortunately, your general HVAC contractor will not deal with mold, and we found that many companies feel the same which is why you may need a specialist.

Businesses that specialize in the removal of mold use many terms like abatement, remediation, and removal to describe the work they’ll do in your home. While the terms essentially refer to the same thing which is the removal of mold and bringing your air quality back to normal levels, the processes they use can vary considerably.

Regardless of the technique, any professional mold removal or remediation service like ServPro will seal off the area they work in with thick plastic along with vents to make sure mold doesn’t enter their home. High-efficiency HEPA filters are used in the cleaning process and some companies can even restore objects that have been covered in mold.

Attics and basements are both popular areas for storage, so finding a professional that can clean and restore certain things is a bonus. Industrial dehumidifiers and commercial mold removal products are common as well. All of these are used by professionals to clean up moldy areas, but when you’re dealing with ductwork, things are different by design.

Companies can use soda or dry ice blasting to make wood covered in black mold look like new in a basement or attic, but those methods won’t work inside duct work. Instead, you’ll need someone certified and approved to deal with ductwork, which may be challenging to find in certain areas. The NADCA or National Air Duct Cleaner Association is a good place to start.

In our research, we were able to find contractors and businesses certified for mold removal without any problems in various states and counties across the United States. Did you know that certain states have laws on the book specifically for mold remediation? Well, they do and the list is shorter than you’d think with less than 20 states with active legislation.

The cost of a traditional duct cleaning can range anywhere from $500 to more than $1000, and that’s without mold involved. Depending on how serious the issue is and the size of your home, you can expect that price to potentially triple. Professional cleaning takes time and requires a variety of techniques as you can see in the video below.

Mold Prevention

Mold can grow anywhere in your home, and while it may start as a small colony in one spot, it can quickly spread to other locations. That’s especially true with HVAC systems by design considering they will spread mold spores throughout your home. Whether you’ve already have your mold problem in check or just want to ensure it never returns, here are some tips every homeowner should keep in mind.

Keep the Temperature in Check…

Do you love to crank the AC up on a hot summer day? Well, the temperature differential can cause condensation to form on distribution lines, vents, and other parts of the ductwork. When that moisture doesn’t get a chance to evaporate, mold and mildew can begin to form. Keep temperature settings in mind, but think about the age of your unit and its size as well.

Having an undersized HVAC system isn’t ideal for obvious reasons, but choosing one that’s too large can also lead to issues. They can cool areas of your home off too quickly which leads to short cycling and a variety of other issues. It can lead to a buildup of humidity which can result in mold. It’s recommended to keep your indoor humidity levels below 45%, and there are machines that can help you do just that.


A dehumidifier can help you keep humidity levels in check whether used in a living area or crawl space in a basement. These machines work to draw excess moisture from the air in a room and allow homeowners to prevent moisture from building up. While commonly found in humid areas, they are often recommended by professionals in areas where moisture is an ongoing concern.

Most dehumidifiers require very little maintenance aside from emptying the bucket and changing the filter. That’s unless it has a condensate pump, however, as you’ll simply need to run a line to a drain and let gravity take care of the rest. The main thing to keep in mind with these machines is durability as you’ll want something dependable that is specifically designed for a basement or attic.

UV Lights for HVAC Systems

hvac uv light for air ducts

Another great way to keep mold and a variety of other airborne bacteria out of your ducts is to consider a UV-C system. There are two styles available as well with UV-C lights designed to sanitize coils and ones geared towards ductwork. Coil-based UV systems ensure that mold won’t build up on the coils inside your unit and keeps it from spreading any further.

They are affordable, easy to install, and come in several single or dual-bulb configurations depending on the size of your home. UV-C lights designed for ducts work in the same fashion and can work continuously or only when your HVAC system is running. 


While you can clean a moldy vent with detergent and warm water or vacuum and ducts for dust, it can pay to go the extra mile where indoor air quality is concerned. That’s why we recommend using a professional if you feel you have mold inside your ductwork and taking the steps we discussed to prevent it from happening again. 

Mold Removal FAQs

Q: What types of mold are usually found in ductwork?

A: There are over a dozen basic types of mold that could be found in your ductwork. Some of the more common ones include Alternaria, Trichoderma, Chaetomium, and Stachybotrys, or Black Mold.

Q: Is it difficult to clean mold from an HVAC system?

A: If it’s only around your vents, and not in the ducts, it’s something every homeowner can handle themselves. If you do feel that mold has infested your ductwork, you will want to call in a professional to clean them.

Q: How quickly can mold make you sick if it’s in your ductwork?

A: If you have an underlying respiratory problem, you could experience anything from itchy eyes to shortness of breath quickly. In other cases, it may take time for the effects to take hold, but you should stop using our HVAC system until it’s cleaned if you suspect mold in the ductwork.

Q: Is there a mold inhibitor or treatment I can use to prevent mold in air ducts?

A: There are a number of products that work to prevent mold and mildew in areas like bathrooms, but a UV-C light is the only feasible option for ductwork.

Q: Can mold grow in air ducts during the winter?

A: Yes. While it is true that mold does need moisture to thrive, it can find plenty of that in the colder months if the ductwork on a house is in poor condition.

Q: Can I use bleach to kill mold or do I need special cleaner?

A: Bleach is actually great against mold when you mix 1 cup of bleach with 1 cup of water. It can cause discoloration on some surfaces including metal, however. 

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