It stands to reason that, if a structure is going to encounter fire, smoke, and extreme heat on a regular basis, then it needs to be built from materials that can stand up to these threats and come out relatively unscathed. This is definitely true for chimneys; if you tried to make one entirely out of wood or plastic, it probably wouldn’t last very long.
We talk a lot about chimney care and maintenance on this blog, but have you ever wondered what chimneys are made of? The answer is actually pretty interesting—and more complicated than you might expect:
We’ll start out by explaining that there are two main types of fireplaces. Masonry fireplaces are what most people think of when they imagine fireplace construction; these hearths are hand-assembled from brick and mortar and are usually installed while a house is being built. They’re literally part of a home’s structure, and—with proper maintenance—can last a lifetime. Meanwhile, prefabricated (or “prefab”) fireplaces are produced in factories and made out of metal. They can be installed in a pre-existing house with relative ease, but their maximum “lifespan” is only about 15 years. Masonry fireplaces are more common in older houses, while houses built in the last few decades tend to have prefab fireplaces.
Let’s be clear: one type of fireplace isn’t necessarily better than the other. Both have their advantages and disadvantages, and both should be inspected and cleaned by a professional at least once a year (or whenever you have reason to believe that something is amiss). But the type of fireplace you have in your home will affect the structure (and appearance) of your chimney. If you’re not sure whether you’re “Team Masonry” or “Team Prefabricated,” you’ll hopefully be able to figure it out by the time you finish reading this post!
The Chimney Itself
If you go outside and look at your home’s chimney, you’ll likely see one of two different setups. The first is an exterior structure that seems to be stuck on one side of the house; the chimney may “cut into” the roof, but it will have a visible body that reaches the ground. If this is the case, then you probably have a masonry chimney. The second possibility is a chimney that seems to simply jut out from the roof of the house without an external body. If that’s what you’re dealing with, then you probably have a prefab chimney.
(Please note our usage of the word “probably” in the previous paragraph. These are not hard-and-fast rules when it comes to chimney construction, so you’ll probably need to consult a specialist to verify the exact type of chimney that you have.)
In masonry chimneys, the structure consists primarily of brick and mortar. They typically—but not always, especially in older houses—have some kind internal liner to protect the chimney flue from damage. This liner can be made out of clay tiles, aluminum / stainless steel tubing, or a cast-in-place material similar to cement or concrete. If your chimney lacks a liner, we strongly recommend you have one professionally installed!
In prefab chimneys, the flue is made completely out of metal and resembles a pipe or a tube. Some folks genuinely like (or are just indifferent to) its somewhat industrial appearance and leave their chimneys looking this way. Other folks choose to encase the visible parts of the chimney in a structure called a “chase.” Chases are essentially façades; they can be made out of brick-and-mortar to give the chimney a more classic look, or they can simulate wood or vinyl siding so that they match the rest of your home’s exterior. Chases also serve to help insulate the chimney and protect it from damage; they’re nearly always aided in this task by a chase cover, which fits on top of the chase like a lid.
Caps and Covers
Regardless of whether a chimney is a masonry or prefab, it should always be fitted with a chimney cap made from stainless steel, painted steel, or copper. A properly fitted and maintained cap will significantly decrease the chimney’s risk of damage from debris, rainwater, and animal activity. Caps can be simple structures or elaborate art pieces. The kind you select for your chimney is a matter of personal taste.
It’s worth mentioning that prefab chimneys often come pre-equipped with a small, round chimney cap that somewhat resembles a bug zapper (or a zoetrope). If the chimney is encased in a chase, then the chase cover will have a hole cut in the center so that the cap is the only part of the “actual” chimney that’s left exposed. Unfortunately, these caps tend to be significantly less effective and more prone to wear than larger, separately-installed caps. A professional technician can help you find a supplementary cap that will work with the existing one (and beautify the structure overall).
Masonry chimneys are valued for their craftsmanship and durability, while prefab chimneys are admired for their convenience and (relative) low cost. Some people have a strong preference for one or the other, and many homeowners don’t care as long as they can use their fireplace. Either way, a chimney is a complex structure that must be installed and taken care of properly if it’s going to be safe to use. You might not be an expert on your chimney (after all, that’s our job!), but knowing the kinds of materials that make up its body and inner workings may help you understand it a bit better.