Anatomy of a Chimney

December 27, 2016

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A chimney is a very complex system and understanding how chimneys are built and how they work can help you to determine why yours does or does not work well. In short, a chimney works because of the differences in pressures between hot and cold air. Ever heard someone say hot air rises? This simple fact is how chimneys work and why they are built the way they are.

How are Chimneys Built?

There are five main parts which make up the construction of a chimney. Each of these portions of a chimney is an important part, but they cannot work without the other pieces. Additionally, these are not the only parts required to build a chimney, but these are the most important, functional parts of the chimney that allow it to work.

The Firebox

The firebox is where you burn the wood. The part of the firebox which comes into direct contact with the most intense heat created by the fire is called the firebrick. Firebrick is much more resistant to fires allowing homeowners to safely have fires inside of their homes. If you do start to see cracks in your firebrick, which will happen over time, call a local chimney repair company before using the chimney again.


The damper is the metal door which closes off the chimney from the rest of your home. Before you light any fires, double-check that the damper is open so smoke can freely flow up the chimney. In the area around your damper is also the “throat”, which is what directs smoke up and around the smoke shelf and into the flue of your chimney.

Smoke Shelf

The smoke shelf is the part of the chimney which traps any smoke or water which makes its way back down your chimney. This helps to prevent any back-draft and also any mess within the firebox.


The chimney flue is where the smoke from a fire runs up and out of your home. The flue consists of a flue lining which helps to shield the surrounding brick and other materials from the heat produced from the chimney.

Chimney Cap

The cap on top the chimney is the final major piece of the puzzle. The chimney cap is placed to allow air flow out of the chimney while preventing any animals or water from entering into the chimney itself.

How do Chimneys Work?

The basic idea of a chimney is that the hot air created from the fire goes up and out the chimney. This creates a flow of air, or a draft. The draft makes it so the smoke going up the chimney does not have an opportunity to slow down and come back down. If the chimney is improperly built, or the flue isn’t the correct size for the fireplace or stove, then back-draft can occur because the air leaving through the chimney cools within the flue itself and sinks.

What affects the amount of draft my chimney produces?

There are two main factors affecting how much draft is produced by your chimney. The first is the temperature difference between the air inside the chimney and the air outside. The second is how tall the chimney is. The relationship between these two factors is such that the hotter the chimney, and the taller the chimney stack, the more draft your chimney produces.

For more information on how chimneys work, or to have a chimney built in your home, get in touch with a local Maryland fireplace installer today. Fireside Stone and Patio is a local Maryland renewable heating, alternative heating, and custom fireplace design, installation, and service company servicing the Clarksville, Columbia, Carroll County and Greater Baltimore areas.