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What are the signs of mold in your air vents? Is mold dangerous? Do you know how to hire a reputable company to clean the vents? Can you DIY?  Come learn all you need to know.


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Filtering Air - black mold on air vents

Filters are the key to keeping mold out of your air vents. Without filtration, the air retains mold spores, dust, and other contaminants.

One of the main reasons your HVAC (Heating, Ventilation, and Air Conditioning) system gets dirty in the first place is through neglect. Forgetting to change air filters, using poor filters, having gaps in filters, or no filter at all(!), affects how clean the system is. Leaking ducts (especially in crawl spaces under homes) can also be culprits for dirt, dust, insects, and even animal droppings.

city pollution - black mold on air vents

Dirty outside air dramatically increases the amount of pollution inside a building.

A dirty nearby environment can also affect your HVAC system negatively. New construction, factories, and nearby highways can increase pollution outside your home or workspace. Dirty outside air dramatically increases the amount of pollution inside a building.



Having mold in your HVAC system is much more common than you might think. In fact, when we check an HVAC system during a mold or indoor air quality inspection, we find mold more often than not.

Mold Inside the Air Handler - black mold on air vents

Inside the Air Handler – Dust (aka ‘mold candy’) builds up over time and encourages mold to grow.

Most of the time the mold is located inside the air handler on the coil. There are two simple reasons for this:

  1. Water is present on the coil when the air conditioner is running. The water is deposited as moisture is removed from the air during cooling. (If you’re familiar at all with our Education Center Blog, you already know that excess moisture usually leads to mold in your home.)
  2. Air filters (or lack of filter!) inadequately prevent dust (aka ‘mold candy’) from being deposited on the coil, usually because filters are of poor quality, do not fit properly, or are missing altogether. Proper air filters changed regularly are one of the most important ways to keep mold out of your HVAC system. (We tell you all about filters later in the article. Keep reading to learn more!)

Once mold has begun growing inside the air handler, mold spores are blown into the home’s living space every time the heat or air conditioner runs. This compromises indoor air quality and can cause additional mold growth inside the ductwork and the home.



stinky smell in home - signs of mold in air vents

They just bought this house, but the musty, moldy smell is overwhelming! Air vent cleaning might be just what they need, or the problem could be much more sinister. What they really need now is a comprehensive mold inspection to see how to proceed.

Do you smell that? Did you forget to wash your gym clothes? Does the dog need a bath? You cleaned everything, and can’t find the stench! It’s so musty! What could it be?! If this sounds like your home or office, you might have a problem with mold and MVOC’s.

MVOC’s or Microbial Volatile Organic Compounds are compounds created by fungi and bacteria during their metabolic processes. MVOC’s can be detected by simply smelling the air. The smell of MVOC’s has been compared to stinky socks, locker room odor, wet dog, or old cheese. They give off a distinctly musty, moldy smell.

MVOC’s can be dangerous and even toxic to humans. MVOC’s can be mycotoxins or can cause allergy symptoms. It depends on which ones are present. Even if you can’t see any mold growing, if you smell musty, moldy odors, you may have a mold problem in your building.

There are also compounds called VOC’s or volatile organic compounds that can be produced by household cleaners, paints, aerosols, disinfectants, air fresheners, glues, and even furnitureVOC’s are not caused by mold or other microbes, and give off a distinctly chemical scent. VOC’s can cause health problems as well.

What Kinds Of Damage Can MVOC’s Cause?

There have been over 200 different chemical compounds identified as MVOC’s that are produced by fungi and bacteria. The chemicals produced include alcohols, arsenics, benzenes, toluenes, acids, sulfur compounds, and many more.

Many but not all of these chemicals are mycotoxins and are harmful to people and pets simply by breathing them in.



mold can be many colors not just black, pets and mold

Mold can be many colors but is always a raised fuzzy growth.

Mold is usually a black, white, brown, green, gray, or yellow, fuzzy growth. Sometimes you can see it. Sometimes you can’t because it is hidden in the dark recesses of your home. Places like atticscrawlspacesbasements, behind cabinets, inside floors, etc. are great places for mold to grow.

Water Damage Leads to Mold

It’s not easy to see mold, but if you have any major water leaks in your home, you are much more likely to find it! Flooding is of course a major problem. Usually people notice when pipes have burst or flood waters have invaded their homes. These are dramatic events!

major water leak

Time is not on your side! Mold can start growing in less than 48 hours!

How long does it take mold to start growing?

alarm clock

Mold can start growing in less than 48 hours! Water behind baseboards and cabinets, wet carpet tack strips, and other hard to reach areas are a ticking mold time bomb. Even with fans going and mopping up the water, it may not be enough to prevent mold growth.

Slow Leaks – A Homeowner’s Worst Nightmare

slow water leak

Slow water leaks like this one can cause more damage in the long run because they go unnoticed… allowing mold to grow.

Tiny cracks in pipes and hoses, and clogs in drains can become a nightmare if forgotten long enough. Tiny leaks over a long period of time can cause as much or more damage than flooding water type events. Because they go unnoticed, tiny leaks can cause more damage than most people realize. Remember we talked about how mold has plenty of food sources in your home? All it takes is that tiny bit of extra moisture and mold starts growing. In most cases it starts within 48 hours!

The main sources for mold growth in homes are water leaks from faucets, roofs, hot water heaters, ground water damage and even sewer backup. Find the water leaks and find the source of the problem.



sneezing mom and child

Yes! Indoor air can retain: household chemicals, volatile organic compounds (VOC’s), mold sporespollenmicrobial volatile organic compounds (MVOC’s), toxins, bacteria, viruses, and other irritants more easily than outdoor air. Infectious bacteria and viruses can cause disease.

Mold in air vents can cause mental and physical health problems including: allergy sensitization, shortness of breathallergic reactionsasthma attacks, and mental health problems including: disordered brain function, changes in balance, slower blink reflexes, slower reaction times, color discrimination problems, and depression.

Man with headache - Is Attic Mold Dangerous?

It is important to note that the longer you are exposed to the mold, the more pronounced your symptoms become. At first, it might just be allergy symptoms, but over time (weeks, months, years) mycotoxins build up in your system, and can make you sicker and sicker.

Not all molds are toxic, but many are. Mycotoxins can cause health problems ranging from poisoning to cancer. You can be affected by mycotoxins even if you are not allergic to mold.

‘Toxic Black Mold?’

Before we go any further, let’s clear up the confusion about ‘toxic black mold.’ When you read about ‘toxic black mold’ it is kind of misleading. The thing is… dangerous and toxic mold is not just black, it can be many different colors. Toxic molds can appear to be green, yellow, brown, and black. Any of the colors you see could be producing mycotoxins. You can’t tell if mycotoxins are present just by looking or smelling. You have to perform a laboratory test.

So, What is a Mycotoxin?Signs of Mold in Air Vents - Mycotoxins

Mycotoxins, literally ‘fungus poison’ in Latin, are secondary metabolites that can be produced by molds, and are not living organisms. Mycotoxins are a byproduct of mold. Not all mold spores produce mycotoxins, but some do. So the molds that produce mycotoxins are the ones that could be categorized as toxic or poisonous.

So, where is the line between an allergic mold and a toxic mold? That line is defined by the presence of mycotoxins, and is NOT defined by color. Mycotoxins are invisible and cannot be detected just by looking at the mold growth.

What Do Mycotoxins Do?

These chemical substances can cause many health problems ranging from mild to severe. Even if you are not allergic to mold, you can be affected by mycotoxins.

Mycotoxins can be absorbed by the body in a number of ways including: through the skin, the airways (inhalation), and through the intestinal lining (ingestion). Detrimental health effects caused by mycotoxins can range from “acute poisoning to long-term effects such as immune deficiency and cancer.” Chronic disease sufferers, such as people with immunosuppressive disorders or underlying lung disease may be more sensitive to molds and mycotoxins in their environment.

cat sneezing, pets and mold

The main ways people and pets become poisoned by mycotoxins include breathing contaminated air or eating contaminated foods. Simply breathing contaminated air can introduce the mycotoxins into your lungs! Foods such as apples, cereal grains, coffee beans, nuts, spices, dog and cat food, and more can become contaminated with fungi that produce mycotoxins. Mycotoxins are NOT something you want in your home!

To learn more about how mold affects your pets check out our article: Mold and Pets – 10 Things You Most Likely Didn’t Know.

To learn more about how mold can affect your health, check out our post: Health Effects of Black Mold.

Please remember that this blog is NOT intended to replace medical advice, diagnosis, or treatment.




Very Dirty Air Duct - black mold on air vents

According to the EPA, there are 3 main reasons you might want to have your ducts or air vents cleaned:

  1. Ducts are clogged with dust or debris and the particles are being released into your home. (Dust plus moisture equals mold.)
  2. Ducts are infested with rodents or insects
  3. There is substantial mold growth inside your heating and cooling system (due to neglect, dust, rodents or insects).
  4. Purchasing or selling a home is another time when duct cleaning may be needed. If you or (the previous owners) have pets or smoked, it is more likely that ducts could be clogged or need cleaning.

If your HVAC system is in a crawl space, it is also more likely to be prone to leaks and mold growth. For more information see our post: HVAC System in Your Crawl Space? You May Be Breathing Dirty Air.



The answer is maybe. If your system is dirty, through neglect, leaking ducts, mold growth, or poor air filtration it could help significantly!

However, people eager and willing to sell you ‘duct cleaning services’ for a gimmick price are all too many! There are a lot of scam artists out there. With no regulation on duct cleaning, it’s easy to get scammed. Before you rush to get your ducts cleaned, keep reading! We tell you all about all the tricks, and how to really get your money’s worth.



Woman looking Disgusted - black mold on air vents

Ugh. What is that musty smell? It might be mold in your HVAC system.

Does your home have a musty odor even after cleaning? Can you see visible mold growth near vents, air returns, or on filters? If you can see it or smell it (musty wet dog or gym bag types of smells), you may have mold in your air ducts.

In addition, if you are constantly ill with allergy symptoms, you may also want to have ducts cleaned. Even if mold is not present, allergens such as dust, pet dander, smoke, VOC’s (volatile organic compounds)microbial volatile organic compounds (MVOC’s), and more can build up in your HVAC system. These allergens need to be removed (not killed) to improve your health.

To learn more about allergens in your home check out our post: Mold Allergy Avoidance – How to Stay Well.

If you have mold inside your HVAC air handler, it’s best to have a professional clean the coil, fan, and the ductwork. This is a service that most HVAC and mechanical contractors offer. Be sure to look at the coil yourself before they close the unit up, or ask for pictures to verify that the contractor has done a thorough jobKeep reading to learn all the questions to ask and how to avoid scams!


Best Mold Removal Companies Near Me

Air duct cleaning is NOT a DIY project. Special equipment is needed to remove dust, dirt, mold and debris. You really do need to choose a professional for this job. How can you choose the right contractor? What questions should you ask them before hiring them? What kind of advertising should you expect?

Duct Cleaning Special, only $39.99!

Duct cleaning 84% off!

$290 worth of services for only $29.00!

What do these three statements have in common? They are all gimmicks to convince you that these companies will really give you an amazing deal. But y’all, when it looks too good to be true, it probably is.

There are a lot of people out there who will try to take advantage of you with duct cleaning scams. They claim you get all these ‘services,’ but what they really do is rip you off.



Don’t let this happen to you! Here’s what you should know when hiring a company to clean your ducts.

Dirty Duct - black mold on air vents

It should not look like this after cleaning!

Top 3 Duct Cleaning Scams

1.Blow and Go – The technician comes in and looks around, gets surface dust and dirt, and then leaves. They typically have many appointments in one day and don’t spend enough time truly trying to clean the ducts. They may not even remove parts to get to the interior of the system.

2.Bait and Switch – That $39.99 cleaning turns into $700 amazingly fast. They bait you with the cheap price, and then up-sell, or even charge for additional work you didn’t agree to have performed! Then, their work is still low quality.

According to the EPA, duct cleaning “services typically – but not always – range in cost from $450 to $1,000 per heating and cooling system, depending on: the services offered, the size of the system to be cleaned, system accessibility, climatic region, and level of contamination.” Any provider that offers a ‘$39.99 duct cleaning special,’ isn’t offering a full service cleaning. There are many scam artists out there. There are also unscrupulous companies who plan to ‘add on’ additional services whether you agree to them or not.

3.Mold Inspection – Scammers prey on your fears, use a cheap coupon or add to get their foot in the door. Then, they tell you you have mold…even if you don’t!

Here’s where we can help. If mold has been ‘found’ by a contractor, put a hold on the job, and get a second opinion.

Here at Branch Environmental, we are experts at mold inspection and remediation. We will tell you for sure if you have a problem or not. Call us or schedule an inspection today!

Especially if you don’t live in our service area, check out our post: How to Choose the ‘Best Mold Removal Company Near Me.’ Use our guide to help you choose the best mold inspection and removal company for your needs.

How to Protect Yourself from Scams

  1. Do your homework – Know as much as you can about the company before hiring them.
  2. Avoid advertisements or specials that advertise ‘whole house cleaning specials’ for less than $100. If it seems too good to be true, it probably is.
  3. Request a system inspection before agreeing to the cleaning.
  4. Ask for proof of insurance. A reputable company should be able to show you instant proof of important documents.
  5. Hire a professional. Does the company have a good reputation? Are they transparent in what they are selling? Can they tell you more about the process of cleaning before you agree to have it done?
  6. We’re Here When You Need Us. Where else could the mold be lurking? When mold is in the air vents, it can easily spread to other areas of your home. We routinely inspect HVAC systems, and can tell you for sure if you have mold. If you do have mold, you want it  all to be removed safely.


changing air filter, routine maintenance - black mold on air vent

The best way to prevent mold from growing is to keep dust out through routine maintenance.

Now that you have a clean HVAC system, how do you keep it that way? You cannot remove all mold spores from the air, or keep the coil completely dry during the summer. The best way to prevent mold from growing is to keep dust out through routine maintenance.

To prevent dust from coming into contact with the coil, choose a high quality, appropriately sized air filter that is changed (or washed) on a regular basis.

Of course, remember to change the filter at least every 3 months, or to wash and replace washable filters every month. For washable filters, it’s better to have two, one to wash, and one to use. When choosing a washable filter, remember that it must be completely dry before putting it back into the system.


All air filters are not created equal. To begin, determine the size of the filter needed. It sounds like a no brainer, but people use the wrong sized filters all the time. Incorrectly sized filters will not filter the air properly causing dirty vents and dirty air. Check out that dirty air filter in the picture below. Now imagine if you didn’t have the filter, or it was the incorrect size. All that ‘gunk’ (dust, mold spores, bacteria, viruses, etc.) would just be circulating throughout your air vents and your home. YUCK! Fortunately, this is an easy fix.

dirty and clean air filter - signs of mold in air vents

Changing filters every three months and having appropriately sized filters is key to mold prevention.

What size air filter do I need?

Especially if you are not sure that the air filter is not the correct size, you should measure the air intake.

  1. Start by turning off the unit. You don’t want air blowing through the system without a filter! (Not having a filter is a great way to increase dust, aka ‘mold candy.’)
  2. Next, using a measuring tape, measure the length, width, and depth of the inside edge of the filter’s slot frame.
  3. Round down to the nearest whole number. The actual filter should be ¼” to ½” smaller than the inside of the frame.

Of course if you think the filter is the correct size, measure the filter to get the correct size to replace it. It can be tricky to measure the inside of the frame correctly. Be sure to measure carefully.

What kind of filter do I need? What is the MERV value?

Filtering Air - HVAC Mold Removal Near Me

Choosing the right size filter and MERV value for your filter is critical to keep mold, allergens, and other particles out of your indoor air.

Next, determine what MERV values your HVAC system can handle. MERV stands for minimum efficiency reporting value, or how efficient your filter is at removing dust, dirt, smoke, pollen, carpet fibers, pet hair and dander, mold, bacteria, and even viruses. The higher the MERV value, the more effective it is at removing all of those nasty things from your air.

Not all HVAC Systems Handle High MERV Value

Not all HVAC systems are created equally either. Some systems can handle using a filter with a high MERV value and others cannot. Find out what MERV ratings your system can handle before purchasing one that is not designed for your system. Be sure to check the system manual or talk to your maintenance technician to determine the correct MERV value and filter size.

Finally, once you know what size and MERV value are best, make your purchase with confidence! Of course, remember to change the filter at least every 3 months, or to wash and replace washable filters every month.


Air Filter Change - black mold on air vents

Regular maintenance keeps your HVAC system cleaner and healthier for everyone. Mold prevention includes:

  1. Changing or cleaning filters regularly
  2. Using the correct size and MERV rated filter
  3. Keeping vents clean and in good working order
  4. Checking ductwork on a regular basis

These 4 steps can prevent many HVAC problems. Duct cleaning can improve your health, especially if you have mold, allergies to dust or pet dander, or have specific problems such as: insect or rodent infestations.

Avoid scams by doing your homework, and request important documents, such as insurance, before technicians arrive. Don’t fall for cheap coupons or gimmicks. If they say you have mold, get a second opinion. Better yet call us, and we’ll tell you for sure!

Branch Environmental Logo

At Branch Environmental, we believe that no one should live or work in a building that makes them sick. We will treat your home like it’s our own. From hidden mold sources to major contaminants, we can identify exactly what is going on in your home and rid it of environmental toxins, often for good.

Branch Environmental – Because nobody should live or work in a building that makes them sick.