There’s nothing more relaxing during those chilly times of the year than building a fire. Grab some hot cocoa, turn on a favorite movie, and dim the lights, and you’ve got yourself the ultimate cozy setup. These structures aren’t always just bringers of happiness and warmth, though. Without proper care and maintenance, mold in a fireplace can turn your favorite cold-weather fixture into a health hazard.

In the chimney, though?

You read that right! While these spaces may not be at the top of our list for hotspot microbial growth locations, they can absolutely get bogged down with contamination. That fungus among us is persistent and resilient, allowing it to pop up in seemingly random places like the holders of that warm blaze.

That’s why it’s important to stay on top of proper maintenance to ensure this particular contamination situation doesn’t happen in your home. Whether you have a chimney now or this fixture is at the top of your “must have” list while home buying, here’s everything you need to know to prevent and handle mold in a fireplace. 

But First, Mold

Before jumping into handling and preventing mold in a fireplace, it’s best to understand a little more about that fungus among us. "Know your enemy," if you will. If you already have a strong foundation of knowledge, you can go ahead and skip this part.

There are over 100,000 species of mold identified so far, and they exist all over the world. Each species reproduces by creating and releasing microscopic spores into the surrounding environment.¹’² If these non-living spores stumble onto a surface with the right elements needed for growth, they’ll put down roots called hyphae and colonize the surface. 

Their ability to grow roots is one of the main reasons why dealing with mold in a fireplace is so tricky because they can reach deep into porous surfaces and be difficult to eliminate. 

Thanks to their hardy nature, most species of mold only need two elements to transition into a living colony.³ 

These two elements are:

1. A food source
2. A water source

If these are present for 24–48 hours, that spore will settle down for the long run and start up the reproductive cycle. All of those spores will then begin to circulate throughout the surrounding area.

Why Does Mold in a Fireplace Happen?

Oddly enough, fireplaces can be perfect locations for this microbial growth. 

All of the organic matter floating around, like particles from firewood, will build up along the surface of the chimney. Add in other random particles like skin cells, and it’s pretty much an edible buffet. 

That leaves moisture as the missing element. With a direct connection to the outdoors, this can occur in a variety of ways. These can include:

• Cracks in the mortar
• Broken chimney crown 
• Damaged chimney cap
• Poor ventilation

Remember, all it takes is for this moisture to be present for 24 to 48 hours for that fungus among us to move in and start growing. Before you know it, one of the issues above can lead to your chimney becoming a hazard zone.

Is Mold in a Fireplace Dangerous?

Yes, it can be. As long as the mold in a fireplace is thriving and surviving, it’s releasing spores and fragments into the surrounding area. Some species of mold also produce microscopic toxins called mycotoxins when threatened.⁴ 

As an added layer of complexity, where mold is found, bacteria are often present as well. This microbial growth further adds to the particle party.⁵ 

In nature, all of these particles have a big, wide world to disperse through. Growth in a home is not the same scenario. Instead, most of those particles will be distributed throughout the indoor space. And, thanks to modern building practices pushing for net-zero energy efficiency, there’s very little airflow between indoor and outdoor environments. This means that a majority of all of those particles will remain inside until they’re forcefully removed.

As long as the colony exists indoors, all of these invisible particles will continue to build up in the home.

The health impact comes due to the size of the particles in question. Classified as particulate matter, these particles are small enough to be inhaled, ingested, and absorbed into the body.⁶ The more time someone spends at home, the more particles will make their way into the body. Some particles are so small that they can bypass the lungs and head straight into the bloodstream.

The immune system will attempt to get rid of all these foreign particles, but it can eventually get bogged down and/or malfunction, triggering a long list of potential symptoms.⁷’⁸’⁹’¹⁰’¹¹’¹²

Common symptoms of mold exposure include: 

• Headaches and migraines
• Rashes and other skin issues
• Joint and muscle pain
• Chronic fatigue 
• Brain fog
• Mood swings
• Anxiety and/or depression
• Allergy and cold-like symptoms 
• Digestive problems 

The tricky thing is that no two people will respond to mold on wood (or exposure in general) the same way. One person may have the occasional headache while another person develops over 30 symptoms.

Much more research is needed to better understand how exposure impacts our bodies, but it’s a tough subject to nail down. Genetics, length of exposure, volume of exposure, species of mold, presence of mycotoxins, presence of bacteria, and immune system status all play a role. Those with compromised and developing immune systems, for example, are prone to experiencing adverse reactions faster and to a greater degree.  

The potential for chronic symptoms is reason enough to actively work to avoid mold in a fireplace and understand how to treat it properly. That way, you’re not breathing in warm, toxic air.

How Do You Prevent Mold in a Fireplace?

The best way to deal with mold in a fireplace is to prevent it from popping up in the first place. Fear not, because there is a list of things you can do to protect your warming fixture.

Here are steps you can take to safeguard your chimney.

1. Clean and Inspect it Annually (at a minimum)

At least once a year, schedule a trained professional to come out and inspect the fixture. During the summer, the fireplace could have been blocked by debris or developed structural issues, leading to poor indoor air quality and possible water intrusion. 

The person coming in should ensure that:

• The cap, crown, and flashing are in good condition and don’t have any damage that could allow moisture to enter
• There’s no debris blocking the chute 
• The flu is operating correctly, so that sooty air gets out 
• The structural foundation of the chimney has no damage  
• Any creosote, a harmful byproduct of burning wood, is removed 

Keep in mind that not all damage is immediately visible. It could be a small crack in the mortar that’s difficult to see, allowing for moisture intrusion and microbial growth. 

If they find any issues with the chimney, resolve them ASAP. The last thing you want is to breathe in harmful air or experience catastrophic issues such as house fires.

2. Opt For a Waterproof Layer

Your chimney is constantly bombarded by varying weather conditions throughout the year. From wind and rain to snow and ice, these fixtures are a line of defense that helps protect your home from moisture intrusion. That being said, the battering and varying temperatures can take their toll on the surfaces and materials of your fireplace. 

As the materials typically used are porous and semi-porous, constant contact with moisture can weaken their structural integrity. Over time, they can degrade, allowing for issues such as leaks and other problems. 

Applying a waterproof coating to your chimney helps add a layer of protection for your fiery fixture. Not only will it help protect against moisture intrusion, but it can also help increase the lifespan of the fixture and prevent cracks in the structure’s materials. There are various types of sealant, so it’s best to consult a professional on which option is best for your particular fireplace. 

Once applied, keep a close eye on the layer and reapply when necessary. Typically, the rule of thumb is to reapply every five years, but consult with a trained professional to determine the right timeline for your fixture.

Pro tip: If there are any structural issues, make sure to fix them before applying a waterproof  sealant. 

As an added bonus, preventing moisture not only helps avoid mold in a fireplace but also helps protect the structural integrity of the fixture itself. Prolonged contact with moisture can degrade the mortar, concrete, bricks, and other materials used in the chimney’s construction.

3. Ensure That There’s a Chimney Cap 

A chimney cap is an added layer of defense against moisture entering your fireplace’s flu, which is essentially an open passageway between the outdoors and the interior of your home. Typically made of metal, wire, and mesh, this object will sit on top of your chimney, directly above the crown, and act as a sort of hat against any precipitation.

This little cap also comes with other benefits, such as protecting the roof from embers, stabilizing the warm flow of air, and preventing animals from settling in your chimney.

Before installing a chimney cap, contact a professional to get their opinion on the best option for your particular fireplace.

4. Regularly Check for Water Intrusion 

Before lighting a fire, grab a flashlight and take a close look all around your fireplace. The sooner you can catch signs of any sort of moisture intrusion or structural issue, the quicker you can begin tackling the problem. This reduces the risk of microbial contamination and will help keep your indoor air quality safe.

It will also prevent structural degradation of the fixture, saving you money and headaches down the road.

How Do You Tell if There’s Mold in a Fireplace?

Speaking of checking for problems, how do you tell if there’s mold in your fireplace or moisture intrusion? Here are some signs to look out for. 

Is There Visible Growth?

When it comes to visible mold, look for any discoloration or abnormalities. With so many species out there, mold can come in all sorts of colors, shapes, and textures, so look for any sort of abnormality. Some of the most common colors include green, white, grey, blue, red, black, brown, or the infamous pink. As for textures, they could be fuzzy, powdery, velvety, or slimy.

Is There Moisture Intrusion?

Water damage is one of the first signs of a potential contamination situation. 

Signs to look out for include:

• A dripping sound
• Dark water stains on the chimney material
• Dampness around the fireplace box

Is There an Odor?

If you don’t find any visible mold or water damage, that doesn’t mean that there isn’t a problem. The growth could be in a hidden location, or be too small to be visible yet. 

In this case, rely on your nose. Mold growth often creates a damp, musty, earthy smell due to the release of gases called microbial volatile organic compounds (MVOC).¹³ If you smell this in the space, there’s a good chance that you’re dealing with mold in a fireplace.

Do You Have Unexplained Chronic Symptoms?

To make matters more tricky, not all mold growth will be visible, and not all mold growth will create a smell. In cases like this, pay attention to your body and how you feel. Have you developed chronic symptoms over time that no doctor can pinpoint a root cause for? Do they flare up anytime you’re near the fireplace? 

Our bodies have amazing warning systems that let us know when something is wrong. If you start feeling unwell, those invisible particles could be making their way inside your body and wreaking havoc, causing your body to sound the alarm and push for you to get out of that situation. Always listen to your body when it’s saying, "Hey, something is definitely not right here."

How to Get Rid of Mold in a Fireplace

The absolute best option for dealing with mold in a fireplace is hiring a team of professionals to handle it. With all of the semi-porous and porous surfaces in the fixture (not to mention the difficult-to-reach location), it’s an extensive and tricky process to remove the contamination. Remember that mold grows roots, which can reach deep within these surfaces. Proper remediation should also include fixing the issue that led to the growth in the first place and installing engineering controls to make sure particles aren’t getting blasted all over the place.

Bring in a Mold Inspector

First up should be a qualified mold inspector. This individual will go through the entire home, determine if that’s the only problematic area, figure out what led to the growth in the first place, and alert you to what contaminants are present, including species of mold, mycotoxins, and/or bacteria.

The individual chosen should spend a few hours at a minimum combing through the interior and exterior of the home and using a variety of methodologies. 

Some of the testing data you should expect to see are: 

• Species of mold present
• Quantities of each mold
• Potential spore presence in the HVAC system 
• Presence of mycotoxins 
• Presence of bacteria

All of this information is needed to understand what’s actually existing in the home so that they can create the right protocol for the unique situation. If other contaminants such as mycotoxins and bacteria are present, the remediation protocol will need to address this. Should spores make their way into the HVAC, this will need to be remedied. Otherwise, those particles will blow all over the home and could turn into a new mold colony. 

Hiring a Remediation Team

After the inspector comes in and collects data, your next step is to find a qualified remediation team to get rid of the mold under the carpet. Like mold inspectors, though, not all remediation teams are built the same. 

Again, you want a company that prioritizes your health, understands the importance of creating a safe environment, and has proven success in remediating toxic homes. Their protocol should be built on three main pillars to ensure proper decontamination. 

These three pillars are:

1. Remediate the sources properly.
2. Identify and address the problems that led to those sources in the first place.
3. Eradicate all contamination created by those sources, including toxins and bacteria.

Failure to hit every point can lead to failed remediation.

If the source that led to the contamination isn’t addressed, the conditions for growth are still there, allowing the problem to come right back. Should the roots of the microbial growth be left behind, the colony can come right back. High levels of contaminants like mycotoxins and bacteria left behind can lead to continued exposure. Each scenario does not lead to a healthy home environment and can allow for any chronic symptoms to persist. 

The last thing anyone wants to do is waste money and time repeating the process while also feeling unwell. The right team should tick all of the boxes above so that when they leave, you have peace of mind knowing that mold in a fireplace is a thing of the past.

Staying Safe and Warm 

When it’s freezing outside, building a fire and sticking indoors are probably at the top of your list of must-have activities. Hanging out with mold in a fireplace is probably not what you had in mind when you were trying to get warm, though. Adding this piece of the puzzle is crucial to making sure you’re safe during those chilly months of the year.

When the average person breathes 20,000 breaths per day and spends 90% of their time indoors, what’s in that air matters! If it’s filled with mycotoxins and mold spores, that can negatively affect your health. Keeping a close eye on those chimneys can ensure that our homes are the safe spaces we want them to be. 

Health begins at home.™

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