Since a fireplace chimney deals with fire and smoke, a damaged or broken chimney part can cause problems or even prove to be dangerous.
Most American homeowners have a fireplace that provides sweet warmth in the living room and ties the whole place together. A fireplace is considered the heart of any home yet most people are unaware of the inner workings or even the basic parts of a fireplace chimney.
The following article discusses the basic parts of a chimney and fireplace and their role in the functionality of a fireplace chimney. We’ll also share with you certain signs that let you know what part might need repairing or in certain situations, a replacement.
But first: why is it important to know about your chimney? Let’s find out.
Why Should You Know About the Basic Parts of a Fireplace and Chimney?
Having an idea about the basic parts of a chimney and their functionality can help you diagnose problems earlier and save you and your family from dangerous situations. It also helps to know a thing or two about chimneys when you’re out in the market looking for one.
If left unaddressed, issues and faulty parts tend to become harder to repair. It increases the cost of the repair and the sheer hassle of having it fixed. Sometimes, a part is in such a condition that repairing is not an option, and you’ll have to get it replaced. So, it’s better to avoid such situations by learning about the anatomy of a chimney and its basic parts.
Before breaking down your fireplace chimney into its basic constituents, let’s talk about the different chimney types.
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Types of Chimneys
Essentially, there are two types of chimneys that people have in their homes these days:
- Masonry Chimneys (Traditional)
- Prefabricated Chimneys (Factory-made)
Masonry chimneys are those old age-old chimneys made from brick and mortar. Unlike the traditional setting where the fireplace and chimney are separate, the factory-made chimney is a one-piece entity with the chimney attached to the fireplace.
Our focus today would be on the anatomy of a masonry chimney and the basic parts that award it such high functionality and durability (We’ll only consider parts that are paramount to the efficient working and safety of the fireplace chimney).
Chimney Diagram: The Anatomy of a Chimney
Here is a detailed description of all the masonry chimney parts that’ll help you understand your chimney better and help you diagnose potential issues in your chimney before it’s too late:
Bricks are the foundation of a masonry chimney. Most masonry chimneys are made up of clay bricks (red bricks). And if they’re not in good condition, your chimney’s structural integrity is at stake.
If left without care and maintenance, cracks can form on bricks and in the masonry joints between them. These cracks enlarge over time and cause severe problems if not properly patched early.
Moisture from rain, snow, and the outside atmosphere can seep in through the cracks of the outer brick layer. And if there’s one thing you should know about chimneys, it’s that moisture is their worst enemy.
Patching these cracks early on can save you thousands of dollars and ensure your safety and that of your family. Thankfully, it’s pretty easy to spot cracks and patch them up. Here’s an easy-to-follow guide on how to patch a chimney. However, you can also get professional assistance.
A flue is essentially a vertical duct that starts from the firebox (where the fire is ignited) and ends at the top. The purpose of a chimney flue is to take exhaust combustion gasses from the fireplace out of your home.
Without a flue, the smoke will have nowhere to go, and combined with heat, it can cause a house fire. Fire can also break loose if cracks inside your flue allow it to get to combustible materials inside your home, e.g., drywall.
A wythe is a vertical, single-brick masonry wall used to separate chimney flues.
Often, houses have a single chimney for various appliances such as furnaces, water heaters, fireplaces, etc. However, all these appliances should have designated flues. A single flue for various appliances is dangerous as harmful gasses from one appliance can be conducted to another via the shared flue.
While multiple flues in a single chimney are allowed, they should be divided by a wythe wall. Also, the partitions should be bonded or tied securely to the chimney, according to NFPA 211-2019.
Chimney flues and liners go hand in hand. While a flue is tasked to remove the exhaust gasses from the house, it is still close to drywall and other materials that can catch fire. A chimney liner is, therefore, placed inside the flue to limit heat transfer and prevent fires.
The liner also keeps the flue bricks safe from harmful byproducts of combustion that would otherwise disintegrate the mortar in between the bricks, creating cracks. These cracks are dangerous because of two main reasons:
- Heat can pass through them, and the nearby combustibles can catch fire.
- CO gas can leak into your home.
There are three main types of chimney liners:
Metal Liners are used to repair an existing chimney and are known for their durability.
Clay Tile Liners are common, especially in older homes, and are pretty cheap.
Cast-in-place Liners are permanent liners that improve the structural strength of the chimney flue.
Found at the base of a chimney stack (a portion of the chimney above the roof), a chimney flashing is essentially there to waterproof your chimney. Depending upon the structure of your roof and your environment, a chimney flashing can be made up of vinyl, copper, steel, or aluminum.
While various types and methods are used for flashing, it all comes down to the kind of chimney and roof you’ve got.
Some of the more common flashing types, used together with caulk, are:
Step flashing – present under the roofing shingles and, along with the chimney bricks, is a piece of L-shaped metal.
Counter flashing – also called cap flashing, is fixed parallel to the chimney and covers the step flashing.
Base flashing – used at the chimney base to keep moisture from entering.
A leaking flashing can be disastrous to your chimney and even your rooms. A leak in the chimney flashing lets the moisture which penetrates into the mortar joints become brittle and break down.
The top of a chimney is called a chimney crown and is usually slanted so that rainwater can be directed away from the chimney. The chimney crown is covered with cement or mortar to insulate the chimney from water and environmental elements that may corrode the chimney.
Since the chimney crown is placed at the top, it’s common sense that it takes a lot of damage which, over time, results in cracks. These cracks are harmful since they allow water to seep in and damage the chimney. Thus, regular checkups and maintenance of a chimney crown are essential for its durability.
While a chimney crown protects the better part of the chimney, the flue is still exposed. Open chimneys are exposed to outside debris and small animals (that can get inside for shelter) and clog the chimney flue. A clogged chimney flue is dangerous as it traps hazardous gasses and exposes you and your family to smoke and CO.
So, a chimney cap, a mesh of stainless steel, is installed. The cage-like structure allows the smoke to escape while keeping rainwater, birds, and small animals from getting inside.
Chimney Chase Covers
Commonly known as chase tops or chase pans, chimney chase covers are rectangular covers that seal the chimney tops. Chase covers are only used for factory-built fireplaces.
A chimney top is open, which means anything from water and dust to small animals and birds can get inside and corrode or clog the chimney. A chase cover ensures your chimney is free of moisture, dust, and anything harmful.
A damper is a mechanism inside the flue that lets you control ventilation. By controlling the airflow inside the flue, you can control the intensity of the fire. But when the chimney is not used, the damper is closed to keep the cold outside air from entering.
Depending on the installed type, there are various ways to open or close your chimney damper. The most common fireplace chimney damper types are:
- Throat Damper ((located just above the fireplace)
- Top-Sealing damper (creates a tighter seal)
If your damper is not functioning properly, there’s a high chance it has been clogged due to debris. You might want to call a certified professional to clean it up.
Shaped like a reverse funnel, a smoke chamber sits just above the damper, connecting the firebox to the chimney flue.
The smoke chamber is designed such that the smoke escapes quickly and efficiently through the flue. However, most smoke chambers are made from corbeled masonry with gaps and steps that trap smoke and soot, creating a buildup.
It is important to parge your smoke chambers so that they are smooth and smoke-tight allowing for an efficient exhaust of smoke.
Sitting right between the smoke chamber and the firebox is a smoke shelf designed to prevent downward drafts and to keep smoke and other toxins from entering your living space.
Parts of a Fireplace
To understand how a fireplace works, knowing the different parts that make up this classic feature is essential.
Often a square or a rectangular box, a firebox is the main part of a fireplace. It’s the place where the fire is ignited.
Fireboxes are made from non-combustible materials (e.g., cement or bricks) to withstand the heat coming from open fires, etc.
Over time, your firebox can form cracks or gaps between the bricks or cement for various reasons such as poor quality construction materials, moisture, frequent expansion (thermal), and contraction.
Before igniting a fire, ensure no spaces or gaps exist. Excessive heat can get concentrated in such areas, which can seriously damage your firebox.
A fireplace hearth is the flooring on which the fire is ignited. It is essentially the base of a fireplace and is made from non-combustible materials such as granite, stone, ceramic tiles, marble, etc.
The hearth ensures that the floor is safe from the heat from the fireplace, which is why it extends into the room. Hearths also serve aesthetic purposes, so you’ll find them in electric fireplaces, even though they’re not mandatory.
But you can’t do without a hearth if you’ve got a wood-burning fireplace or stove.
A fireplace mantel is a shelf on top of a fireplace used for aesthetic purposes. Traditionally, fireplace mantels were used to catch smoke from the fire before it entered the room. But now, the only need for a mantel is to tie the room together with a visually pleasing design and to place various items on top of it.
Fireplace mantels are installed in either of the following two ways:
- As a standalone floating mantel, like a shelf on top of a fireplace.
- As a part of a fireplace surround.
A fireplace lintel is a bar that lends structural support to the chimney and protects it from intense heat and successive fires. Traditionally, wood was the material choice, but nowadays, stone, concrete, steel, or brick lintels are common.
Since bricks and mortar joints become weaker over time, there’s a risk of the chimney falling into the firebox. A fireplace lintel keeps it from happening while also increasing the chimney’s life by protecting it from excess heat.
A fireplace face, made of non-combustible materials, surrounds the outer front of a fireplace. While a fireplace face is there to protect the surrounding walls and materials from the heat coming from the fireplace, it also serves aesthetic purposes.
Often confused with a fireplace face is a fireplace surround. A fireplace surround doesn’t serve any purpose apart from being an aesthetic bridge between the fireplace and the room. Fireplace surrounds can be attached to traditional masonry fireplaces and prefabricated ones.
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When thinking of fireplace dangers, we often think of the ‘worst-case scenarios’ like burning houses or chimney fires. However, we often disregard scenarios that might be less dangerous than chimney fires but are much more common. Fireplace glass doors help keep you and your family safe from such dangers.
From burning logs tumbling to red hot coals jumping out of the fireplace, glass doors keep us safe.
Apart from protection, glass doors contain ash and other fireplace residues, allowing for a cleaner room. These doors are also great for conserving energy as they keep the cold air out (in winter) and the cool air within the room (in summer).
Fireplaces are not as efficient as one might think. That’s because a traditional fireplace drafts the hot air up the chimney while cooler air from outside is dragged into the room. Due to this, a lot of heat is wasted.
To improve the efficiency of a fireplace, fireplace inserts are used. Covered by cast iron or steel, fireplace inserts are fireproof boxes that create a closed combustion system. Some of them even come with blowers to pump in the hot air.
While there are three main types of inserts: wood, gas, and electric, gas and electric inserts are much more efficient and easier to operate.
The ash dump is located directly below the ash door (usually made out of cast iron or aluminum and vented). It is the space where the ash falls whenever the ash dump door is opened as per need. A typical ash dump has an opening area of about 4 inches by 8 inches.
This opening provides the space for the ash to fall directly onto the ash pit, from where the ash can later be cleaned.
Under the ash dump is an ash pit surrounded by concrete or cinder blocks. Accessed through the cleanout door, the ash pit collects all the ash from the fireplace. It would be best to clean the ash pit frequently as it may clog the cleanout door. Ash pits range from small to large areas usually based on the type of fireplace installed in the house.
The cleanout door is often located in the house’s basement and is usually made of cast iron (for minimal warping). The purpose of a cleanout door is to access the ash pit. Old ash collected in the pit is shoveled through the cleanout door. The door opening is about 8 by 8 inches.
The footing is a horizontal surface directly under the ashpit and the chimney’s foundation. The footer of a fireplace chimney is a 1-foot thick concrete layer that supports the chimney. It is usually located in the basement.
The foundation of a chimney, made out of reinforced concrete, would be around 12 to 24 inches thick, often connected to a small number of grade beams. The foundation is located below the ash pit section of the chimney. Its sole purpose is to provide stability from the ground to the chimney by distributing the weight of its whole structure over a large area of ground.
Fireplace mortar is the type of mortar usually used in chimneys. Firebrick joints should be around a quarter-inch thick. And the best mortar for this purpose is the ASTM refractory mortar. This type of mortar should be protected from water (which may cause it to deteriorate).
A fireplace chimney is at the heart of your home and like the heart, is quite critical. Understanding the various fireplace chimney parts such as the chimney flue, liner, smoke chamber, glass doors, fireplace inserts, etc. is crucial to a safe and efficient fireplace.
Therefore, we have discussed the various fireplace chimney parts in detail, how they operate, and what purpose they serve for you to understand their importance. And finally, we talked about different warning signs to look out for before lighting that fire.
Hopefully, you are better positioned to diagnose any issues and call professionals before it’s too late. But if you still have questions about fireplace chimneys, let us know, and we’ll be glad to help.