How to Handle Mold in Chimney: Homeowners Guide

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If a musty and unpleasant smell is coming from your chimney, there’s probably mold growing inside. Mold in chimney not only smells bad but can also cause health problems and can damage your chimney and different parts of your house beyond repair.

You should never let mold growth go unnoticed. Make sure to remove the mold immediately to avoid further growth and damage. You can use simple methods to remove it or, better yet, hire professional help.

Let’s discuss mold removal and prevention methods, but before that, it’s important to understand what causes mold to grow inside your chimney.

What Causes Mold in Chimney?

Mold thrives in humid and chilly environments, typically where moisture accumulates. 

Below are some factors that contribute to moisture in your chimney and facilitate mold development:

Poor Ventilation

Mold loves poorly ventilated areas. Such as the damper of an unused chimney

When the damper remains closed, ventilation is obstructed, allowing moisture to accumulate inside. This lack of ventilation leads to mold growth, which is commonly observed in chimneys that have been inactive for extended periods.

Damaged Chimney Crown

A chimney crown is present at the top of your chimney and is made of concrete. The chimney crown overhangs the edges of your chimney to prevent precipitation.

Since chimney crowns are in direct contact with the outside elements, it’s common for them to deteriorate over the years. If not given appropriate care and routine maintenance, your chimney crown may develop cracks, leading to water leakage and mold growth.


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Cracked Chimney Cap

broken chimney cap causing mold smell in chimney

The chimney cap plays a crucial role in safeguarding your chimney from rain, debris, and small creatures. Positioned at the top of the flue opening, the cap is susceptible to cracks and significant damage due to the following:

  • Strong storms
  • Exposure to outside elements
  • Rust
  • Improper installation

A cracked chimney cap cannot prevent water from entering your chimney. That is why a cracked chimney cap is a common cause of mold in chimneys.

Lack of Waterproofing

The upper section of your brick-and-mortar chimney is exposed to rain and harsh weather, which can cause wear and tear over time. As cracks form, water seep inside the structure, creating an ideal environment for mold growth.

To prevent this, it is essential to waterproof the top section of your chimney. Make sure you use materials that contain polysiloxanes or silanes, as they do not obstruct the pores of your chimney mortar. This allows interior moisture to escape while simultaneously preventing external moisture from entering.

That is why it’s important to waterproof your chimney top stack. Make sure to use a material that contains polysiloxanes or silanes. Such materials don’t block the pores of your chimney mortar, allowing inside moisture to escape while preventing outside moisture from getting inside.

A chimney stack that hasn’t been waterproofed will start to crack early and increase the chances of mold growth.

black mold in chimney

What is the Risk of Having Chimney Molds?

If left unaddressed, mold in chimneys can lead to various problems, including property damage, unpleasant odors, and further deterioration. Extended exposure to mold may also pose significant health risks. The following are some primary concerns associated with chimney mold:

Bad Smell

Mold growth, a common source of disagreeable odors in chimneys and fireplaces, can worsen if not addressed. As it expands, mold releases a stale, musty aroma similar to rotting wood. The intensifying smell can result in considerable distress and annoyance.

Health Risks

Mold spores spread in the air and cause allergic reactions and other mild to more serious symptoms in most people. Here are some of the symptoms of mold exposure:

  • watery eyes
  • sneezing
  • wheezing
  • runny nose
  • coughing
  • itching
  • tiredness
  • Headache

People allergic to molds or have asthma show more serious symptoms, such as fever and difficulty breathing. Studies have also shown that some children exposed to mold developed asthma, especially those genetically susceptible to it. Mold exposure can also cause hypersensitivity pneumonitis in people susceptible to it.

Property Damage

Mold in the chimney can cause deterioration of the brick and mortar, and it can also spread to different parts of your house, including your attic and roof. Since mold eats away organic matter, your house materials, such as wallpaper, floorboards, drywall, carpet, and ceiling tiles, are unsafe.

mold inside the attic is one of the signs of mold in chimney

At first, you’ll notice fuzzy patches and discoloration on your chimney, house walls, and other parts of your house. But if given enough time, the mold can weaken the foundations of your walls, ceilings, and floorboards, causing them to break down.

If you detect and remove the mold early on, you’ll have to deal with less damage.

Mold in Ducts

Homeowners usually expect mold to grow in attics, basements, or chimneys, but molds can also get inside your HVAC systems. This can be quite troubling not just because it’s hard to remove mold from these ducts but also because, from here, the mold disperses throughout your home. The air blown into different parts of your home carries the mold that wreaks havoc.

That is why, if you suspect mold inside your HVAC system, turn it off immediately to stop the spread of mold. Hire a professional service to inspect and remove the mold from the ducts to prevent further damage.


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How Do I Get Rid of Mold In My Chimney?

Here’s how you can remove mold from your fireplace, chimney, and other areas of your home:

The DIY Method to Remove Mold

Here’s a simple step-by-step guide to removing mold growth in a chimney and other parts of your home:

  1. Since different mold types can spread so easily, you first need to check different areas of your home for mold growth.
  2. Once you’ve located all areas with molds, it’s time to remove the mold. For that, you need the following:
    An antifungal cleanser.
    • Bleach/water solution (1 part bleach, 10 parts water), vinegar, or tea tree oil if a cleanser is unavailable.)
    • A stiff brush (with a long handle)
    • Since mold can grow in difficult-to-reach places inside your chimney and fireplace, it would help to have a mirror and a flashlight
  3. While cleaning, wear a mask and gloves to prevent the mold from causing any allergic reaction.

Note: When you remove mold from your carpet or drywall, the spores can spread into the air. So make sure that doesn’t happen, or the problem will worsen.

Repair or Replace

Removing mold from glass, metal, and concrete is less hassle. On the other hand, wooden surfaces are harder to clean.

If the mold is still in its early days, remove it from the wooden materials, such as floorboards, and repair the damaged portion. But, if the mold has been allowed to grow for a while, the damage can be severe. You can’t remove the mold; replacement is the only viable option.

Since you can’t remove wall studs, the mold must be sanded. You’ll need to apply a sealant on any remaining mold.

It’s Better to Hire Professional Help

While you can opt for a DIY mold removal process, hiring a professional is better. Here’s why:

  1. Mold can grow on hard-to-reach places inside your home’s chimney, fireplace, and other areas. Non-specialists may need help accessing or even identifying these locations. Expert cleaners have specialized equipment and experience, enabling them to detect and reach such spots.
  2. Mold removal can be a challenging and time-consuming process. Professional services possess the necessary tools and workforce to complete the task efficiently.
  3. During the cleaning process, there is a risk of mold spreading. Experienced professionals implement precautionary measures to prevent this from occurring.
  4. ​​If you are already experiencing symptoms of mold exposure, removing mold yourself can exacerbate the issue. Professionals with safety gear can handle the removal without further affecting your health.
  5. Professionals can thoroughly detect and eliminate mold from all areas of your chimney, fireplace, and home. They can also address any water leakage issues to prevent future mold growth.

How Much Does It Cost to Remove Mold from Chimney?

On average, a mold removal project would cost around $2000 to $4500. But this is just a rough estimate. The actual cost can vary largely depending upon various factors, such as:

  • Area of the mold infestation
  • The extent of the damage done

The total cost will also increase if you also want extra services such as:

  • Chimney waterproofing
  • Chimney cap installation
  • Chimney crown repair
  • Roof leak repair, etc.

How Do I Prevent Molds From Forming In My Chimney?

Prevention is always better as it saves you from all the costs of repairing damages. The number one thing you need to do to prevent mold growth in your chimney and fireplace is to conduct annual chimney inspections and regular chimney sweeping and maintenance. The NFPA also recommends annual chimney inspections as it prevents many chimney problems.

Since mold growth occurs because of moisture, ensure no chimney leaks occur. Ensure your chimney cap and crown are properly installed and in good condition. You can further prevent water leakage by waterproofing your chimney brick and mortar.

Also, make sure to use your fireplace frequently. The fire from the fireplace will kill the mold in the fireplace. Moreover, the heat from the fireplace will dry the air and remove any condensation in the upper portion of the chimney preventing mold growth.

The Takeaway

Mold in chimney is a serious issue, not only because of its mold smell but also because of its health and safety risks. If left to grow, the mold can eat away your home’s mortar, wood, and other organic materials, causing severe damage. The repairs can be costly, so removing the mold as soon as possible is important.

While you can remove the mold yourself, hiring a professional for the best results is best.

Once the mold is removed, make sure to take precautionary measures to prevent the mold from growing.

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Thomas Green

Thomas has worked in the Chimney & Fireplace field for over 12 years. He is an expert in his trade and loves to help People with their needs. Thomas Write helpful articles so that homeowners can make the most informed decisions about their fireplace and chimney.