Chimney Anatomy

The chimney anatomy is made of of many components. Before learning about these components first we need to know just what is a chimney?

A chimney, in simple terms, is a vertical chamber that is designed to allow combustion products from an appliance or fireplace exit to the outside atmosphere.

The Basic Anatomy of a Chimney

The Chimney structure is normally made of block or brick. In a chimney there can be multiple flues or separate passageway's. These flues are the passageways for the smoke and gases to pass through to the outside atmosphere. It is best to have only one appliance or fireplace venting into a flue. If your home has a furnace and a wood stove your chimney should have two flues to accommodate them.

NOTE: The anatomy of a factory-built chimney contains only one passageway for venting, the inside of the pipe.

Types of Chimneys

Flue liners are what lines the chimney and keeps the gases in the chimney and out of your home. All modern masonry chimneys are constructed with this liner for safety reasons, ease in cleaning and increased performance. There are several different types of flue liners. Among the most common are: terra cotta, stainless steel, aluminum, and cast in place. Terra cotta is the orange part of the chimney you usually see sticking out of the top of the chimney.

For metal factory built chimney, the inner wall of the chimney also serves as the chimney liner.

The crown is the top of the masonry chimney. The crown should be slightly sloped. This slope is to ensure that rain water runs off the chimney top. The crown should also have and overhang of about 2 inches to shed the water away from the masonry. Most flue liners extend above the chimney crown at least two inches. In some chimneys the liner may extend higher than this depending on local building codes. This flue liner is what is usually the most visible part of the top of chimney from the ground.

How can I Repair the Crown?

The clean out door is located at the base of the each flue. It is usually a small door made of metal. When cleaning your chimney, debris will loosen and fall to the base of the flue. This debris can be removed through this clean out access. There is however an exception to this definition. A fireplace does not need a clean out door due to the fact that soot and debris will fall into the fireplace opening and can be accessed from there.

If you have a metal door that is located below the fireplace it is most likely an ash pit. The ash pit is where you deposit your ashes via a small door on the floor of the fireplace.


When maintaining your chimney, all parts of the chimney anatomy should be checked to be sure they are in proper working condition. This list of things will also be checked by a chimney professional should you decide to hire one.

The main concern of every homeowner is safety. Every year lives are lost and property is destroyed due to the improper care and maintenance of the home's chimney. A quick monthly inspection should be done during the heating season just to be sure that there are no problems forming. A professional check should be done yearly to look for the problems that only a trained eye will see.

As a homeowner there are some easy things that you can check for.

  • The first check that can be performed is a visible look at the outside of the chimney. Check for any visible cracks, holes, or loose or missing bricks. Look for crumbling mortar joints and chipped or cracked blocks or brick. Be sure that the chimney is not leaning or pulling away from the house.
  • The next easy step is to open the clean out door. If you see small pieces of flue, or dust like material that is orange, you know your flue liner is disintegrating. You are at HIGH risk of a blocked chimney and carbon monoxide poisoning.
  • While you are in the clean out door you can use a mirror to look up the chimney, and if it is perfectly straight you should be able to see light. If you see light this does not mean automatically the chimney is clean and in good shape, it just means the chimney is not completely blocked. If you see something that doesn't look quite right, don't panic. It takes a trained eye to determine just what is taking place in a chimney flue. NOTE: If the chimney is exposed in the attic area, be sure to check the condition of that portion also. The first part of the chimney that starts to deteriorate are the mortar joints.
  • If you have a metal factory built chimney, look for loose sections, bending, corrosion, stains and if there is any movement of the chimney in windy conditions.
  • Check to be sure that there is a chimney cap in place. Water from rain and melting snow will gradually damage the inside of the chimney. If your cap is equipped with a mesh screen, be sure the screen is intact and not clogged with leaves, nests or other debris.
  • Next you want to check for any leaks or stains on the inside of the home in rooms near the chimney. Stains on the wall, dampness near the chimney or peeling wallpaper/paint are sure signs of a problem. The problem may be the result of a leaky roof flashing or more likely it could be missing or damaged flue tiles. If this is the case consult a chimney professional.
  • Last but certainly not least is the heating appliance and connecting pipes. If you have a wood stove or insert, check the condition of the pipe and connectors from the appliance to the chimney. Check for rust, holes and soft spots. If any of these things are found, replace the pipe immediately. The first place the corrosion starts is on the under side of the stove pipe. Check the outside of the stove or insert for any cracks, rust, bulges and warping. These are all signs of damage and wear.

    If you have a fireplace, be sure that the damper is working properly. Open and close it several times to be sure it works with ease and does not bind and closes completely. look up in the fire place with the damper open, into the smoke chamber above the damper and make note of any soot build up. If there is a build up it is wise to clean your chimney at this time. Anything more than 1/4" of creosote is a risk for a chimney fire.

    The Fireplace Flue

    If you have a furnace it is wise to leave that maintenance to a furnace technician. You can however check the connector pipes for signs of damage or wear.

    The Furnace Flue

    Safety Alerts

    Never check a chimney flue that is currently in operation. Make sure that fires are extinguished, furnaces are turned off and hot coals are not present.

    Always wear protective gear. Eye and hand protection should be used when looking up into a chimney flue.

    Pipes could still be hot! Be sure to use caution when touching or handling pipes and connectors. Wood burners gloves should be used at all times.

    Open clean out doors slowly. There could be a considerable buildup of soot and debris at the base of the flue.

    If performing your check of the chimney from the roof be sure to use a stable and trustworthy ladder.

    More on chimney safety

    Self checks of your chimney should never take the place of a professional inspection but it can catch a problem forming. Most importantly it will give you peace of mind each time you light a fire or hear your furnace kick on. We live by the rule: “Family First”. Go to top of Chimney Components" The DIY Chimney Liner Resource