What Does a Chimney Liner Do?

A chimney liner is a protective barrier inside the chimney flue, typically made of clay, metal, or ceramic. It serves three main purposes:

1. Protecting the Home from Heat Transfer – The liner prevents high temperatures from reaching combustible materials, such as wooden framing or drywall.
2. Containing Smoke & Toxic Gases – It directs harmful gases, like carbon monoxide, safely out of your home.
3. Preventing Creosote Buildup & Chimney Damage – A well-maintained liner reduces creosote accumulation and protects the chimney’s masonry from corrosive byproducts.

When the liner is cracked or damaged, all of these protective functions are compromised.

The Dangers of a Cracked Chimney Liner

1. Increased Risk of House Fires

Cracks or gaps in the liner allow extreme heat and sparks to escape into the surrounding chimney structure and nearby combustible materials. Over time, this can ignite a fire within the walls of your home, often going undetected until it’s too late.

2. Carbon Monoxide Poisoning

One of the most dangerous consequences of a damaged liner is carbon monoxide (CO) leakage. A properly functioning liner channels smoke and toxic gases out of your home, but if it’s cracked, these gases can seep into your living spaces, posing a serious health risk. Symptoms of CO poisoning include:

• Dizziness
• Headaches
• Nausea
• Confusion
• Shortness of breath
• possibly even death…

Since carbon monoxide is colorless and odorless, a leak can go undetected without a CO detector.

3. Structural Damage to the Chimney

A chimney liner also protects the brick and mortar from the corrosive byproducts of combustion. Without a properly sealed liner, moisture, smoke, and acidic residues can erode the masonry, leading to:

• Brick spalling (flaking or crumbling bricks)
• Deteriorating mortar joints
• Leaky chimneys
• Expensive structural repairs

4. Reduced Fireplace Efficiency

A damaged liner can negatively impact your fireplace’s draft and airflow, leading to:

• Poor combustion (fires burn weakly and inefficiently)
• Smoke backing up into your home
• Increased creosote buildup, which raises the risk of chimney fires

If your fireplace isn’t working as efficiently as it used to, a damaged liner could be to blame.

5. Higher Repair Costs If Left Unchecked

Ignoring a cracked chimney liner can lead to escalating damage over time. What may start as a small crack can eventually lead to major masonry deterioration, water damage, and even mold issues. Additionally, some insurance companies may deny coverage for fire or smoke damage caused by an unmaintained chimney.

What to Do If Your Chimney Liner Is Cracked

If you suspect your chimney liner is cracked or damaged, take these steps:

1. Schedule a Professional Inspection – A certified chimney sweep can conduct a video inspection to assess the condition of your liner.
2. Consider Relining Your Chimney – Depending on the damage, relining with a stainless steel, cast-in-place, or new clay tile liner may be necessary.
3. Prevent Future Damage – Regular chimney maintenance, waterproofing, and installing a chimney cap can help extend the lifespan of your liner.

Conclusion

A cracked chimney liner is a serious issue that should never be ignored. It can lead to house fires, carbon monoxide exposure, and costly chimney repairs. Scheduling annual chimney inspections and addressing liner damage promptly will help keep your home and family safe. If you suspect an issue with your chimney liner, contact a professional chimney technician as soon as possible.