Air Duct Cleaning For Mold

By: Licensed Mold Assessor Brad Fishbein

September 23, 2017

Without a shadow of a doubt, one of the most misunderstood parts of the indoor air quality, HVAC, and Mold Remediation industries is the concept of air duct cleaning for mold.

Some people think it is an absolute necessity.;

Others think it is a downright scam


We are going to put those thoughts in a pot and stir it up to come out with

The Truth,

The Whole Truth,

and Nothing But The Truth..

jack nicholson

…At least as it relates to cleaning air ducts for mold.

In this guide, we will discuss:

  • How Mold Grows In HVAC Ductwork
  • Can All Ducts Be Cleaned
  • Who Cleans Them
  • How The Ducts Are Cleaned
  • How Much You Expect To Pay To Have It Done
  • Is It Worth It To Have Them Cleaned


Throughout this article, you will see the words beneath. Don’t worry! I don’t expect you to be an expert, so here are what we are referring to:

Air Ducts, Air Conditioning Ducts, Air Conditioning Ductwork, Ductwork, Ducts- These words are all used to describe the same thing. It’s a system of tubes that generally run through the attic that are used to circulate air throughout the home for your heating and air conditioning system.

HVAC System- This stands for Heating, Ventilation, and Air Conditioning. Basically, it’s your air conditioning system.

Air Handler Coils- These are also referred to as evaporator coils. It is located inside the air handler ( The indoor HVAC Unit). It is a component that is essential in producing cold air.

Particles- For this particular article, we are talking about little fragments of mold spores, dust, dirt, or fiberglass that usually can’t be seen with the naked eye but can affect the air quality.

Grills- When referring to air conditioning, it is a metal or plastic frame that goes over each register. It has deflectors you can both open and close them.

How Mold Grows In HVAC Ductwork

Check this out:

I am going to dispel a rumor and it is going to sound pretty strange, but mold does not actually grow on air conditioning ductwork.

I know, you are saying to yourself,

Well that means duct cleaning is a scam

Slow down there cowboy/cowgirl…

Let me explain:

While mold does not grow on the ductwork itself, mold will settle on the dirt, dust, and debris within the ductwork. The same goes for the HVAC air handler coils.

Why Mold Doesn’t Grow Easily On The Ductwork

The inside of your ductwork is likely made of or coated with one of three types of materials:

  • Fiberglass
  • Metal
  • Plastic

mold in ducts

There are some older ductwork that may be made of galvanized steel or aluminum, but the three listed above are the most common ductwork materials you will find these days.


Even Fiberglass is a little bit outdated, however, I do come across fiberglass ductwork pretty often in older homes. The fiberglass insulation coating’s main advantage is that it helps absorb sound coming from the HVAC unit.

Mold will not generally grow on the Fiberglass because it is pre-treated with anti-microbial chemicals to prevent mold from growing


Metal ductwork is also very common in older homes. Metal is considered semi-porous.

Here’s the thing:

Mold will generally not grow on metal but under the right conditions, it most certainly can.


Plastic ductwork is much more common in newer homes. The type of plastic ductwork is called flex duct. While the exterior is usually some for of polyester, the interior is plastic.

Plastic is also considered semi-porous so yes, mold can grow on the plastic under the right conditions, it is not very common.

Can All Ducts Be Cleaned?

If you talk to five different air conditioning workers, you will get five different answers. Really, the question shouldn’t necessarily be whether or not the ducts can be cleaned. The correct question should be: To what extent can the ducts be cleaned?


This is a very important question.

The reason why this is such an important question is that if the HVAC ducts are not cleaned correctly, it can be counterproductive and contribute to other issues with air quality.

Cleaning of the ducts is not something that is always feasible, however sanitizing them is and we will get more into that a little later on.

Problems That Cleaning Duct Work Can Cause

We will get into who should clean your ducts a little more in depth below, but the most important thing is that you find somebody that’s competent.

Let’s look at the reasons why:


Some methods that companies using involve using a tool called a wire duct brush. This can be used as an electric power tool. If the operator of the tool is not careful this can damage the interior of the ductwork.

I’m sure whichever company causes the damage will fix it at no cost, but here’s the problem:

They may not realize they caused damage right away.

This can actually lead to mold and I will include a real-life story where that very issue occurred for me:

The client noticed that there was some possible mold present in one of the bedroom closets. During a mold inspection, clues led me to the attic space above. When I got in the attic, there was an odor present and visible mold on some of the structural wood. There was also condensation on the exterior insulation of the ductwork. As I was crawling through the attic, I suddenly felt cold air.


The mixture of cold air leaking from the ductwork and hot air in the attic space led to condensation and mold growth. Mold was also growing within the inner walls of the closet below.

Come to find out the ducts were cleaned with a wire brush approximately 3-4 months before the inspection. The operator of the tool must have scrubbed so hard that it put a hole through the ductwork including the exterior insulation. That is not easy to do!

Oh, and the company that did the duct cleaning accepted no responsibility and last I heard there was a lawsuit still pending.

Bottom line:

Damage can not only lead to monetary responsibility but can also cause mold.

Can Cause Other Particles To Enter The Air

This is particularly true when cleaning fiberglass ductwork.

You see:

the fiberglass lining in the ductwork is generally rolled onto the duct board. When this is scrubbed it can cause fiberglass particles to enter the air.

Then my friend,

You will be breathing in fiberglass. This can cause all sorts of health problems. Some of the health problems that have been linked to the inhalation of fiberglass include:

  • Lung Inflammation
  • Asthma
  • Cancer

Who Cleans The Ductwork?

The obvious answer here would be an air conditioning specialist but if you are talking about cleaning mold from the HVAC ductwork, would it make sense to have a mold specialist clean it?

Let’s explore this…

On one hand, you have the Air Conditioning Specialist who is licensed to clean air conditioning units but is not licensed to clean mold (mold licensed laws don’t apply in every state)

On the other hand, you have a licensed mold specialist who is licensed to clean mold but not clean air conditioning ducts.

Mold Professionals Cleaning HVAC Ductwork

Mold remediation professionals are generally called into a job when there has been a significant leak and mold growing on building materials. This can also include a mold problem that was caused by the HVAC system not functioning properly.


That does not mean they know how to clean the ductwork. Remember, some of the material that ductwork is made out of can be delicate and cause further problems not related to mold growth if not cleaned correctly.

HVAC Professionals Cleaning HVAC Ductwork

Keep in mind that the mold that grows on the ductwork is not actually growing on the duct work and is not likely considered viable (active growing).

Cleaning the mold within the ductwork does not involve and containing building material.

You do not need to hold a licensed to use the chemicals to sanitize the ductwork.

Bottom Line:

This is all something the HVAC professional should be able to perform.

Verdict: HVAC Professional Should Be Cleaning Mold From The Ductwork

How The Ducts Are Cleaned

cleaning mold on ductwork

So I am not going to take you from A-Z on how to have your ducts cleaned.

Why is that?


If you read the section above, I recommend having the ducts cleaned by an HVAC professional

…And I’m not HVAC Professional.

I will, however, give you an outline of what your air conditioning company should be doing.

Keep in mind that the process of cleaning the ducts may vary based on what your ducts are made of. The outline below is assuming you have flex duct but we will also go over the process if you have fiberglass a little later on.

Setting Up A Work Area

A ton of particles will be stirred up in the air during the process.

That’s why it’s important that some your furnishings be covered. For example, a sheet of plastic should be put over a bed if a vent is present


Plastic should be put on a floor in front of a return. This process could get messy.

Take Off All Grills So The Returns And Registers Can Be Cleaned

The grills need to be removed so the ducts can be accessed. All the grills should also be wiped down with a biodegradable solution.

You ever notice some staining like this on your grills:

mold on vents

This is surface mold and should be cleaned. It is recommended that the cleaning be done outside the home.

Seal The Registers

This will prevent any unwanted particles from being pulling into the air while the process is being set up.

Remove The Blower In The Air Handler

The blower will be located in the air handler itself. During this process, the coils from the air handler may also be cleaned if mold is growing on them.

This article is dedicated to the ducts, however, if you do have your coils cleaned it is usually done with a biodegradable solution or throuwashing.ess called acid washing. This is normally an additional charge and is not a normal part of the duct cleaning process depending on which company you use.

It is entirely possible for your ducts to be absolutely filthy but your coils are clean. I see it all the time.

Set Up A Negative Air Machine

The negative air machine has something called a HEPA filter in it. Negative air allows all particles to be sucked into the HEPA filter instead of the particles just floating around in the air.

The negative air machine can have tubes that hook up inside your ductwork to act as a vacuum to suck all dirt and debris right out.

HEPA Vacuuming

The negative air machine will generally get the smaller particles, but in order to get the heavier particles, the technician will generally use a special vacuum.

This usually has an extension to clean deep into the registers.

Lightly Brush

The technician will then use something called an Angel brush to further clean the ducts.

*** SUPER IMPORTANT: This should be done on the lowest speed and very lightly so the ducts are not damaged.

It should also be done with negative air set up to be the most effective when it comes to removing particles.


This is the most important part.

An anti-microbial solution is then fogged into the ductwork. The ducts should still be under negative air when this is done.

Once this is complete the registers should be resealed and still left under negative air pressure.

HEPA Vacuuming All Return Plenums

The process on contact cleaning with a HEPA Vacuum should be done on all the return plenums.

Final Cleanup

After all that is completed, final cleanup should be done.

How Does The Process Change If You Have Fiberglass Ductwork?

mold on fiberglass ducts

Chances are that even if the inside of the ducts is not fiberglass, your plenum still may be.

During the brushing process it is absolutely imperative that if brushing is done, it is done VERY VERY VERY LIGHTLY

Here’s the thing:

I would not do any kind of brushing with fiberglass. It’s just not worth it. That being said I know of a few HVAC companies that do brush fiberglass. It’s not my preference.

As a matter of fact, if HEPA Vacuuming is being completed it should also be done super lightly.

So if brushing and Vacuuming aren’t done, how do you clean fiberglass ductwork?

Glad you asked…

Sealing Fiberglass With Anti-Microbial Paint

If there is excessive dirt, dust, and mold on your fiberglass ductwork, you can simply just replace the ducts.

O wait…

I forgot about the part where it can cost THOUSANDS OF DOLLARS to do that!

Another option is painting your ducts with anti-microbial paint.

The anti-microbial sealant does two main things:

  1. Encapsulate dirt, dust and microbial growth
  2. Inhibits mold growth on the surface

This is a much more affordable and feasible option.

How Much Does Air Duct Cleaning Cost?

how much does duct cleaning cost

Obviously, the price will vary based on the size of your home.


I am going to give you the pricing of the duct cleaning based on a reputable HVAC business that I work with very often. Their pricing is considered reasonable.

They charge:

$26 per register.

An average 2000 sq foot home has 15-20 registers. Based on that it would be $390-$520.

If you want to have the coils cleaned it’s $375 per air handler.

Is It Worth It To Have Your Ducts Cleaned?

mold in ducts

Let’s face it:

The duct cleaning industry kind of has a crappy reputation.


It’s as simple as if your ducts are dirty, you should have them cleaned.

There is no exact time period you should follow. Over time your ducts are bound to get somewhat dirty.


The duct cleaning industry kind of caught a bad rap and that’s why you may hear some people claim the industry in a whole is a scam, but it’s simply not true.

Just like any other industry, duct cleaning companies can scare you into getting the work done. I’m here to tell you not to fall for it. You don’t need to be a professional to stick your head in the ducts and see for yourself. If the amount, of dirt, dust and possible mold is present enough to make you feel uncomfortable, then you should have your air conditioning ductwork cleaned and sanitized.

Have you had any experiences with having your ducts cleaned? If so, how much did it cost you?

Did you notice any difference in the air quality?

I want to hear from you! Tell me about your experiences.

Meet the author: Brad Fishbein is an ACAC council-certified Microbial Investigator. In the fall of 2012, he became a Licensed Mold Assessor in the State of Florida through the Department of Business & Professional Regulation. Brad has helped homeowners with over 5,000 successfully completed Mold Inspections since 2009.

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