How to Determine Whether Your Flue Needs a Chimney Liner

There are many reasons why your chimney may need a chimney liner. The tiles in your flue may have cracked for any number of reasons. If these tiles are damaged in any way the chimney is not safe to burn and should be relined with a stainless steel liner prior to use. The clay flue tiles in the flue system

This liner has been cracked and must be replaced before it is safe to burn.
This liner has been cracked and must be replaced before it is safe to burn.

can become damaged in many ways. If a chimney fire occurs in your flue system the extreme heat may crack the flue tiles. The chimney flue is not intended to actually contain fire, only the products of fire which would be the gases that vent up through the chimney. If something causes a fire to start up in the flue system, say a bit of nesting is in the chimney and it catches fire, the heat can crack the flue tiles.

A shifting foundation may also cause flue tiles to crack. If the home is settling or the foundation shifts significantly it can cause a crack in the flue tiles. When there are cracks in the flue tiles the heat in the

flue system is able to reach combustible parts of the chimney. This is the reason that chimney relining must occur; it prevents fires in the flue system which can spread to the rest of the home. Chimney repair after a chimney fire is not cheap.

Your clay chimney liner has mortar joints in between each tile. If the liner is missing mortar joints the chimney cannot be burned until a liner is put in for similar reasons to those of cracked flue tiles. The missing mortar joints expose more of the chimney than should be exposed, making it more likely for any combustibles to combust.

The only real way to tell if your flue system has experienced any of these conditions, whether it be cracking or missing mortar joints, you must have your chimney swept and a video inspection of the flue system run. It is extraoridinarily difficult for a sweep to check out each individual flue tile for cracks or missing mortar joints by merely shining a flashlight in up the chimney. Using advanced chimney inspection tools, such as video cameras which are planted into small rods with lights, enables sweeps and homeowners alike to see what is going on in the flue system. Similarly, pictures can be taken using such equipment which can be used to make insurance claims if a chimney fire has occurred.

Another reason you may need to reline your chimney is if the chimney’s current chimney flue liner is too large for whatever it is venting. If you are experiencing draft issues or smoking problems, relining your chimney may be the way to go. An improperly sized flue may cause your chimney to not be able to draw properly. If you install a new stove or an insert it is generally required by the manufacturer and by NFPA 211 to have a chimney liner. If you are experiencing a draft issue or have a smoking problem you may be in a situation requiring a chimney liner.

Clay Lamb
Latest posts by Clay Lamb (see all)

12 thoughts on “How to Determine Whether Your Flue Needs a Chimney Liner

  1. Very Helpful. I’ve just had a chimney sweep clean and inspect our chimney. He found cracks in the flue and said the flue should be replaced with a liner. I was doubtful of the recommendation. The chimney sweep DID have pictures of the inside of the flue that showed there were cracks and recommended a liner. Your information is consistent with his recommendation.

  2. My whole house is filled with smoke every time my downstairs neighbors burn their fire place.
    Now all of my things smell like a bomb fire. I wonder if they need a chimney reline.

  3. This could be the issue or not. There are many factors to a smoke problem. It is a process of elimination. I would have them contact a Chimney Sweep for an evaluation.

  4. If you have a solid brick chimney, and a clay tile is missing a mortar joint or has a minor crack in it, what is going to catch fire or combust due to that missing joint or minor crack? Answer, nothing.

  5. John, thank you for your comment. For starters, most brick chimneys are not “solid.” They are hollow on the inside to allow for the expansion of the clay flue tiles inside.

    From my experience, you would be shocked to see how often wood is found inside of that space, not to mention directly on the other side of that brick. Gaps in the mortar joints that are often as thick as an inch, as well as minor cracks in the flue liner which expand when the tiles are heated up, can easily introduce hot gases to combustible material the liner was designed to protect. Exposed combustible material can warm to the point of combustion within 3 1/2 hours.

    That also does not take into consideration the amount of carbon monoxide the home can be exposed to if the flue liner is in bad shape.

    So, for several reasons, missing mortar joints or even the smallest of cracks can introduce serious hazards to your home.

    Burn safe and warm,


  6. The chimney system /flue, “Must be able to contain the products of combustions” (Smoke, gases Fumes etc)
    Think of it as like having a straw with holes in it. But now we are talk about gases within the living space of your home.
    A missing mortar joint as you referenced, on a 12″x12″ flue tile seaming equals a 4 ft long crack?
    …this is not good thing!

  7. I have a question about a home I am looking at. The home has a prefab chimney, but it has a clay flue liner in it. I have never seen a clay liner used with a prefab chimney, only see it with a masonry chimney. Can you help? Is this allowed? or not? If not, what do the codes state about this type install?


  8. By what you’re describing it doesn’t seem to be a proper ul listed prefab fireplace installation and i would not recommend using it. recommend consulting with a member of the national chimney sweep guild to video, they’re probably going to tell you the same thing, you shouldn’t use it.

  9. My clay tile liner has completely shattered and is gone. I want to install a fireplace insert. With no tiles lineing the brick chimney. What do u suggest to use to make my home safe?

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.