If you’ve ever sat around a campfire, you’ve likely noticed sparks and embers rising up from the flames. This is common with fires — even the ones that you build in your fireplace.
The problem, though, is that these floating sparks don’t often die out very quickly. In fact, sparks can float out from a chimney, catch on some dry grass or wood, and ignite a fire that can get out of control very quickly.
A spark arrestor is designed to help prevent these accidental fires, ensuring safety for your home, your neighborhood, and even your region.
But what is a spark arrestor? How does it work? And how do you find the right one for your chimney?
At HY-C, we’ve been manufacturing spark-arresting chimney caps for over 75 years. And in this guide, we’re going to tell you all about them in depth.
We’ll cover what spark arrestors are, the kinds of appliances and machines that use them, how to pick the right one to maximize a balance of airflow and safety, and much more. By the time you’re finished here, you’ll know everything you need to know about choosing the right spark arrestor chimney cap.
What Is a Spark Arrestor?
A spark arrestor is a physical barrier (usually made from metal mesh) that stops stray sparks from leaving an emissions system. The mesh is designed to let the emission system function properly, allowing airflow to pass through while keeping sparks from getting past.
What Does a Spark Arrestor Do?
In an emission system, a spark arrestor is installed at a junction within the system. Stray sparks come into contact with the spark arrestor’s mesh, fizzling out on contact.
In an engine like those on a car, dirt bike, boat, or truck, spark arrestors keep sparks from coming into contact with flammable materials like oil or gasoline.
In a chimney system like those in a fireplace or a wood stove, the spark arrestor mesh is part of the chimney cap itself. The metal mesh of the chimney cap catches stray, floating sparks, preventing them from coming into contact with flammable material on or around your property.
Chimney Spark Arrestor
So, if you want to stop sparks from coming out of your chimney, all you have to do is install some wire mesh on the flue, right? Well, it’s not quite that easy. A simple mesh sheet will still allow rainwater inside the chimney. Instead, you need a chimney cap.
Chimney caps serve three vital purposes:
- They keep precipitation out of your chimney flue
- They keep nuisance wildlife out of your chimney flue
- They arrest sparks that float up your chimney flue
The size of the cap’s spark-arresting mesh is very important. Chimney caps need to prevent sparks from escaping while also allowing smoke and other flue gasses to vent out.
If the mesh is too big, the chimney will vent properly, but it won’t catch many sparks.
If the mesh is too small, it will catch plenty of sparks, but the ventilation will be compromised, increasing the likelihood of smoke and carbon monoxide backing up into your home.
That’s why manufacturers pay special attention to the net free area (NFA) of a chimney cap’s mesh — the size of the open area between the metal. This is why we manufacture two different types of chimney caps: those with ¾” mesh and those with ⅝” mesh.
¾” Mesh Chimney Caps
At HY-C, we’ve been manufacturing chimney caps with spark-arresting capabilities since 1947. During that time, we’ve come to learn quite a bit about venting, mesh, and spark arresting. It’s allowed us to develop and tweak our caps to keep all of these necessary variables in balance.
We’ve determined that ¾” diamond-shaped chimney cap mesh provides the necessary net free area to arrest sparks while ensuring a good draft in the chimney.
In the image above, the cap’s mesh is represented by the blue lines. The red area is the unblocked negative space between the metal mesh.
This image represents the percentage of the total area covered by the mesh (in blue) and the total net free area (in red) left unblocked by the mesh.
On a cap with ¾” mesh, about 84% of the sides of the chimney cap is left open to provide proper ventilation. The remaining 16% is dedicated to arresting sparks. This 84/16 balance is just the right amount to ensure a good draft while also blocking sparks.
⅝” Mesh Chimney Caps
While the ¾” diamond-shaped mesh is what we would recommend in nearly all cases, some areas of the United States have strict regulations around spark arrestor chimney caps.
In many of these areas, year-round rainfall and general moisture levels are relatively low. Because of how dry they are, these locations are much more prone to wildfires caused by stray sparks.
Local codes in these areas require a tighter ⅝” diamond-shaped mesh to catch more sparks than the standard mesh.
In the image above, the tighter ⅝” mesh is represented by the blue lines. The red area represents the unblocked negative space between the metal mesh.
This image represents the percentage of the total area covered by the mesh (in blue) and the total net free area (in red) left unblocked by the mesh. That leaves about 79% of the sides of the chimney cap open to provide proper ventilation and about 21% dedicated to arresting sparks.
The ⅝” mesh’s 79/21 split is great for spark arresting, but its lower net free area can potentially interfere with the chimney’s draft. This lower NFA, combined with other factors, can cause harmful flue gasses to roll back into your home.
This is why we recommend only using chimney with ⅝” mesh in areas where local codes require them. California is one of the most common states to require this tighter chimney cap mesh. For this reason, caps with ⅝” mesh are often called California Chimney Caps.
How Do You Choose the Right Chimney Cap?
Spark arresting is a very important capability of a chimney cap — but it’s not the only one. When looking for a chimney cap, there are four factors to consider:
- The metal the chimney cap is made of
- The chimney cap’s mesh size
- The dimensions of the cap
- The cap’s installation method
To find the right cap, take all four of these aspects into consideration. When you find the right one, it will not only arrest sparks, but it will also keep nuisance wildlife out, prevent rain from getting inside your chimney, and improve the overall health and lifespan of your chimney and fireplace.
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