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How to Build a Fireplace Chimney

Arun Prabhu Dec 24, 2018
Building a classy fireplace is probably what is on every home owner's mind. Keep reading ahead to know about a fireplace chimney, how to build it, and precautions to be taken with the chimney.
A fireplace, to most, is what really adds value to the place, making your house a home. Homeowners will pride their abodes with a masonry fireplace, keep it maintained, and use it as their primary source of heat. It should be noted that, however great you want to make your fireplace and its chimney, you are in the end, playing with fire.
Therefore, care, knowledge and precision, come before good looks, when it comes to building a fireplace chimney. After all, you wouldn't want your house burnt down because of it, or have to bear with a back draft of fumes every time the wind blows into your chimney.
Before you start off with building a brand new, you should know a couple of rules that go with it. These rules are meant to keep peril at bay and ensure a safe fireplace. Also, following these guidelines will help simplify the procedure.

Rules to Build a Fireplace Chimney

This rule is known as the 2-3-10 rule or the 10 foot / 2 foot rule, which states that the lower section of the chimney from the roof penetration point must be clear from the top termination point of the chimney by at least 3 feet.
Its height after this point is decided by all objects in a 10 feet radius around it. The height must be at least 2 feet above anything within a 10 feet radius.
The masonry must be lined.
There will be other rules regarding type of masonry used, fuel used, clearance from flammable materials, etc. Most of them will be localized, so be sure to follow the local rules as well.
You will need to build a proper support frame for your chimney, as it is quite a heavy construct. An ideal way would be to give it a concrete footing of 8 to 12 inches, that stretches for at least 6 inches in all directions from the chimney.
It should be built such that it is least 4 inches larger than the flue in all directions. So if you're using a 10"×10" flue liner, your chimney should be 14"×14". The outer part must be at least 2 inches away from anything that may float up the flue. Place the chimney cap on top of the flue lining and fill the gap between them using a silicon sealant.
If you live in areas that experience seismic activity, it is advised to use #4 reinforcing bars to strengthen the structure, preferably in the brick cells. Grout the bars into place. If your chimney is too small, you can anchor the reinforcing bars closer to the flue.
In this case, you will need to wrap the flue beforehand with ceramic fiber paper. This will protect your flue from direct contact with the rods whenever they expand due to heat. Line your chimney with tiles that can withstand extreme temperatures or temperature fluctuations, like vitrified fire clay tiles.
The cap should be such that no water, animals or birds, can enter the chimney. A way to make sure high velocity winds do not enter through the cap is to give it an angled outflow, like a Spanish Conquistador styled wind directional cowl.
Fortify the masonry every 18 inches with a steel ladder. Anchor your chimney to each floor and roof in case it is an exterior version.


The cap should be able to keep all moisture from entering into the flue. Also, building a cap completely out of mortar is a bad idea, as it will not be strong enough. Water is one the fireplace's biggest enemies.
Water aids in the corrosion of the cap and work downwards into the flue. Take note of all the different materials that you use in building the chimney. They will all have different coefficients of thermal expansion, and this will become a problem if two different materials are packed too closely together.
Be careful whenever you use sealants, and keep a close watch wherever there are any gaps for some time after starting to use the fireplace.
Making your own fireplace chimney can take long hours to complete, but anyone into home improvement will find the task very rewarding. They do add an aesthetic quality to your home and often display the home owner's state of mind. So just let the guidelines point the way and add your own styling where possible, to mark the structure as yours.