Chimney Anatomy 101 – How to Tell Which Type of Chimney & Fireplace You Have

Different heating appliances and chimney systems are prone to different issues and require different types of maintenance. So, knowing how to properly use and maintain your heating appliance starts with knowing which kind you have.

Let’s start with prefabricated chimneys vs. masonry chimneys. What’s the difference?

Prefabricated vs. Masonry Fireplaces: How to Tell the Difference

Fireplaces come in two general types: masonry fireplaces and factory-built (or prefab). Figuring out which you have will only take a moment of detective work on your part. So, grab a flashlight, and let’s get started.

• • • A masonry fireplace has a firebox built of individual firebrick (typically yellowish in color), and if you shine a light inside and look up past the damper, you will see a roughly pyramid-shaped affair also built of brick. A masonry fireplace will also have a brick chimney above the roofline.

• • • A prefab fireplace generally has a firebox made of cast refractory panels. Usually, some metal is visible in the space all around the firebox, and if you look up past the damper, you should see a round metal chimney. Above the roofline, you’ll see more of that round metal chimney, sometimes surrounded by a simulated brick or siding chase housing.

Basic Anatomy of a Prefabricated or factory-built Fireplace

Although similar, there are some important differences to know about when it comes to care and things to look out for. Let’s go a little deeper into the prefab and masonry chimneys before we talk about the differences between stoves, fireplaces, and inserts…

Masonry Fireplaces – What You Need to Know

Masonry fireplaces, built of brick, block, or stone and mortar, are massive structures, often weighing between six and seven tons. They are aesthetically pleasing, long-lasting, and they add real value to your home.

Unlike prefabricated fireplaces, masonry fireplaces are built on-site, brick by brick. The result is that the mason has ultimate control of the final product.

What does that mean for you as the homeowner? It means there is a wide range of masonry fireplaces available – you can have one custom built to meet your needs. And with a little care and periodic maintenance, your masonry fireplace can give you a lifetime of enjoyment.

What common problems do masonry fireplaces have and how can you prevent them?

#1 Settling

Masonry fireplaces require extensive footing for support, or they can shift and crack, allowing the fire to escape to nearby combustibles. If you have a masonry fireplace, you should always keep an eye out for any signs of settling or movement. One weak spot where settling often first appears is where the facing meets the firebrick inside the firebox.

How do you prevent settling?

You can keep settling problems to a minimum by directing downspouts away from the fireplace area and by sloping the ground around the fireplace, so that water runs away from the structure.

#2 Masonry Damage/Water Damage

Although masonry is quite durable, it’s not indestructible – especially not the masonry on a chimney. While the rest of the brick on the house receives some protection from the eaves, the chimney is exposed to every raindrop and freeze/thaw cycle.

How do you prevent masonry damage?

Choosing a quality chimney cover, keeping your crown in good shape, and investing in a chimney waterproofing treatment are the top ways to protect your chimney against water damage and avoid expensive repairs and the need for a chimney rebuild.

#3 Firebox Damage

The firebox (the area of the fireplace that holds the fire) takes the brunt of the fire’s heat, which is why it requires special attention. Over time, the joints between the firebrick will fail from the constant expansion and contraction that comes with heating and cooling temperatures.

The mortar joints (made of refractory mortar) will decay even faster if the fireplace lacks a chimney cover. This is because rainwater will come down into the chimney, pool on the smoke shelf, mix with the soot behind the damper, and form an acidic slurry that can eat away at those mortar joints.

How do you prevent firebox damage?

The key is to keep joints in good repair by ensuring a high-temperature refractory mortar is used and that you’re doing everything you can to keep rainwater out of the chimney and fireplace.

#4 Flue Liner Damage

Most masonry fireplaces have tile chimney liners, which can last a long time if they’re properly maintained and not exposed to chimney fires. One good chimney fire will usually crack flue tiles, rendering them ineffective.

How do you prevent flue liner damage?

You can prevent flue liner damage by keeping up with sweepings and inspections. The general rule of thumb is that a masonry fireplace should be swept before 1/8” inch of soot accumulates. Chimney sweepings will remove corrosive byproducts that could damage tile liners, and inspections will reveal other possible contributors to damage, like chimney leaks.

Note: If you experience a chimney fire, it’s very important that you have the chimney swept and inspected before you use it again.

Prefab Fireplaces – What You Need to Know

Factory-built or prefabricated (prefab) fireplaces are relative newcomers to the fireplace scene. Unlike traditional masonry fireplaces, most factory-built fireplaces are metal and come from the factory as complete units – with a firebox, a specific chimney system, and all necessary parts.

With proper installation and maintenance, your prefab fireplace can give you years of great service. That said, they are prone to their own issues.

What do you need to consider and look out for with prefab fireplaces?

#1 Be cautious about making changes.

The factory-built fireplace and chimney are engineered to work together as a complete system. Both units (fireplace and chimney) undergo testing together, then are listed specifically for use with each other. That means, you have to be very cautious about making any changes to either the fireplace or the chimney.

#2 Installation must be precise.

Because of the specifications and testing around factory-built fireplaces, the installation instructions must be followed exactly, especially the specified clearances from combustibles. Most manufacturers require no less than 2” of air space between the chimney components and all wood framing. If you are installing a new unit, be sure to strictly adhere to these clearance instructions.

If you already have a unit installed, it is very important that you check these clearances whenever possible. Any wood that is too close to the chimney will undergo a process called pyrolysis, and even catch fire at temperatures as low as 200 degrees. (Fireplaces can generate temps of 1000+ degrees and chimney fires can burn at around 2100 degrees Fahrenheit.)

A trip to the attic to check clearances is time well spent, considering that most of the prefab units inspected by chimney professionals are improperly installed. But inspecting the firebox clearances is much more challenging.

#3 Prefab fireplaces aren’t made for excessively heavy use.

Most factory-built fireplaces are tested and listed as decorative heating appliances and will not withstand excessively heavy use. Although they are tested to UL standards, severe over-firing and chimney fires will often badly damage these units.

The best way to ensure you can enjoy your prefab fireplace for years to come is to schedule regular yearly maintenance and carefully monitor for any issues or signs of overuse.

#4 Nesting birds love prefab chimneys.

Many prefab chimneys – especially older units with imitation brick housing above the roof – seem to be preferred nesting sites for birds in many areas. It’s not unusual for chimney sweeps to remove buckets of nesting material from these chimneys. If it’s not removed, nesting material can catch fire or block critical air passageways between layers of metal chimney pipe, causing the chimney to overheat. Both scenarios routinely cause house fires.

Unfortunately, most aftermarket chimney covers are insufficient at keeping birds out and can often make the problem worse. So, what can you do to prevent birds from nesting in your prefab chimney and creating a fire hazard? Schedule annual chimney inspections and invest in a properly sized chase cover and a chimney cap with screening.

#5 Prefab fireplace systems aren’t forever.

The reality is that prefab fireplace systems eventually wear out. Models go out of production and manufacturers go out of business. So, keep a close eye on an aging unit, and be prepared to send old faithful to the great recycling plant in the sky before she fails completely.

Fireplaces, Inserts & Stoves: Which Do I Have?

Alright, onto fireplaces, stoves, and inserts. How do you know which you have? Let’s talk about the differences…

• • • Fireplace – A fireplace is a heating appliance that is built into the home and vented out through a chimney or venting system. Typically, the firebox of a fireplace is made of refractory brick or refractory panels.
    • Fireplace Insert – An insert is a metal heating appliance that is essentially retrofitted into an existing masonry fireplace and vented out through the existing chimney or venting system.
    • Stove – A stove is a freestanding heating appliance that is vented through the wall or roof using stove pipe. Stoves are typically made of soapstone, cast iron, or other metals.

[Show image of each type – fireplace, stove, insert]

Fireplaces, stoves, and inserts are available as wood-burning, pellet, or gas-fired, and each can be a great, long-lasting, and comforting heat source for your home.

Do This One Thing Every Year, No Matter Which Type of Heating Appliance or Chimney You Have…

No matter which type of chimney system or heating appliance you have, follow the National Fire Protection Association (NFPA) Standard 211’s recommendations and have your system professionally inspected by a CSIA-Certified Chimney Sweep® each and every year. That way, you can keep your home in great condition and enjoy the warmth and comfort your fireplace, stove, or insert provides for years to come.

Finding a qualified pro near you is easy – just click here and enter your zip code to get started.

And don’t forget to head over to our Ultimate Guide to Using Your Fireplace for more tips!

If you’re wondering about Chimney Sweeping Logs, we have answers for you! Find that as well as other helpful information as part of the Homeowner Resources page.