Anatomy of a Wood Burning Masonry Fireplace Chimney
While many of us think our wood burning fireplace chimney is a simple, almost indestructible feature of our home, your chimney is actually a complex system that is very vulnerable to damage. From the firebox of your wood burning fireplace to the chimney cap or chase, your chimney and fireplace can have up to 22 parts and are susceptible to many types of damage.
As the saying goes, knowledge is power. Learning the basics of chimney anatomy will help you troubleshoot problems when they arise and can help you and your chimney sweep to be on the same page when you have conversations about your fireplace and chimney. When you know the lingo and understand how the parts of your chimney are supposed to operate, it will be easier for you to understand when your chimney sweep tells you about damage found during an inspection and will help you communicate more effectively if you discover problems that need fixed.
The inside of a chimney normally consists of 7 parts:
1. Smoke Chamber: Above the firebox of your fireplace is a chamber with a sloping wall that compresses the smoke and helps funnel it into the flue. This chamber is called the smoke chamber. It prevents smoke and ash from billowing into the room and allows those combustion byproducts to evacuate more efficiently.
2. Smoke Shelf: You can think of the smoke shelf as the floor of the smoke chamber. Like the smoke chamber, it facilitates the movement of smoke and ash up the flue. It also catches any debris or water that come down the chimney.
3. Damper: Between the top of your fireplace and the smoke chamber are doors that are operated by a pulley or lever, these doors are called the damper. When your fireplace is being used, the damper doors need to be open to allow the smoke and ash to go up the chimney. This also allows air to feed the fire. When your fireplace is not in use, the damper should be closed to prevent your heat and air conditioning from escaping up the chimney. If you do not have a chimney cap, the damper doors are also the last line of defense to prevent rainwater and animals, like birds and bats, from getting into your home.
4. Flue: The flue is the long passageway within the chimney that combustion gases move up through to the outdoors.
5. Flue Lining or Chimney Lining: Most flues have a lining to protect the flammable materials in your home surrounding the chimney—the walls, ceiling and roof—from catching fire and to protect the chimney’s masonry from corrosion and damage from the buildup of combustion byproducts like creosote (a flammable substance produced by burning wood). Flue liners are made of either clay tile, ceramic or metal. They are such an important safety feature that it is essential to not use your fireplace without a chimney liner.
6. Chimney Crown: The chimney crown sits on the top of a chimney and protects it the chimney from water damage. The integrity of a chimney can be compromised when water seeps into the brick and mortar. It can result in mortar deterioration, brick flaking and the collection of unsightly salt deposits. A good crown that is properly sealed prevents this from happening. Typically, chimney crowns are made from concrete.
7. Chimney Cap: The chimney cap prevents water from going down your chimney. Chimney caps must have screens to prevent glowing ash from starting a roof fire. Chimney caps with screens also prevent birds and other animals from nesting in your chimney. If your chimney is without a chimney cap and screen, it is essential to have one installed.
If you have a factory-made chimney then very likely you have a Chimney Chase. That is the name for the structure through which the factory-made chimney pipe runs. If you have a chimney chase, it is required to have a Chimney Case Cover to protect the chase from water, like a chimney cap.
As you can see, every part of a chimney has a very important function. If one part is not working properly you could face a number of problems from unwanted animals getting into your home to a chimney fire that spreads to your house. The goal of our fireplace & chimney professionals is to catch small problems before they turn into big ones. If you notice issues with the components of your chimney, contact a local certified chimney sweep.