A chimney cap’s job is a balancing act. If a cap provides too much coverage, it will restrict airflow in your fireplace and cause a downdraft, resulting in smoke in your home. If a cap provides too little coverage, unwelcome rain and critters could get past it and into your fireplace.
The key to maintaining this balance is through the chimney cap’s metal mesh. Chimney cap mesh sizes are intentional and carefully measured. They allow chimneys to draft properly while sealing out pests and precipitation alike.
At HY-C, we make chimney caps with ¾” mesh and ⅝” mesh. So, why are there two sizes available? Is one size better than the other? And in which cases should you use which size?
In this guide, we’ll answer those questions and more. By the time you’re finished here, you’ll understand the differences between chimney caps with ¾” mesh and ⅝” mesh. You’ll also know which sizes to use in which scenarios, and, most importantly, which size to use on your home.
Chimney Cap Mesh: Spark Arrestor
Ideally, fire and sparks should never come out of your chimney. Embers escaping from a flue tile is a sure sign of a chimney full of debris or creosote. Chimney fires are dangerous, and you should have a chimney sweep out once or twice a year to make sure your chimney is clean.
Many homeowners with wood burning fireplaces don’t keep up with regular chimney maintenance, though. As a result, chimneys throughout the country carry the potential to omit sparks when the fireplace is in use.
In wetter, humid environments, this isn’t as big of a problem. In dry environments, however, a single floating ember or spark from a wood burning chimney could lead to a house fire or even statewide forest fire.
Since most locations in the United States aren’t dry and arid, chimney caps with ¾” mesh are the industry standard. This mesh is tight enough to prevent many critters from getting into a chimney yet open enough to facilitate a proper draft.
Some states with dryer climates, though — particularly California and Oregon — require a tighter, ⅝” chimney cap mesh by law. ⅝ of an inch is about as tight as chimney cap mesh can get while still allowing for a good draft. At the same time, the tighter mesh provides more surface area, preventing sparks and embers from escaping, floating down, and causing a wildfire.
Chimney Cap Mesh: Height
In general, chimney caps are essentially made from three components:
- The metal base (or band)
- The mesh sides
- The hood
Chimney caps (particularly the hood) need to be high up enough above a flue tile to allow air to draft properly inside a chimney. If the hood is too low, a proper draft will be prohibited, causing smoke and other gasses in the chimney to back up and pour from the firebox out into your home. Best practice is to allow for around 6 inches between the top of the flue and the hood of the cap.
Homeowners and installers don’t have to worry about mesh heights with single-flue chimney caps, because the mesh bends inward at a 90-degree angle inside the cap, resting directly on top of the flue tile. In other words, the hood of the cap will be the same distance from the top of any flue it’s installed on.
Multi-flue chimney caps are a little more complicated. They aren’t installed directly on top of a chimney’s flue tile. Instead, they’re installed on the chimney’s crown — the concrete portion from which the flue tile protrudes.
Because of this, you have to be cognizant of the flue tile’s height when choosing your multi-flue chimney cap’s mesh to allow for the recommended six inches of space between the top of the flue tile and the chimney cap’s hood.
For example, if a flue tile sticks out only two inches from the chimney crown, a cap with an eight-inch mesh height will leave six inches of space. If the tile sticks out eight inches from the crown, you’ll need a multi-flue cap with a fourteen-inch mesh height to provide six inches of space.
Chimney Cap Mesh: Animal Exclusion
If you’re at all familiar with the concept of animal exclusion, you know that mesh size is vital to wildlife control operators. When installing a soffit vent cover or a foundation vent cover, the mesh on the screen needs to be tight enough to exclude certain critters, but open enough to allow proper ventilation.
When it comes to chimney cap mesh, the truth is that size doesn’t make much of a difference for excluding wildlife from a chimney. There’s only a 0.125” difference between ¾” and ⅝” mesh, and the standard ¾” mesh is already small enough to keep out chimney-dwelling critters like raccoons and chimney swifts.
Still, you never know what curious critters may get up to, and there may be some cases where that extra ⅛ of an inch may be the difference between keeping a small bird out and winding up with a nest in your chimney. If you want to err on the side of caution, ⅝” mesh is the way to go.
Which Size Chimney Cap Mesh Should You Get?
There’s a lot to consider when buying a chimney cap. Material and dimensions tend to be the first aspects people consider, but mesh size shouldn’t be overlooked. And by now, you know all the ins and outs of ¾” and ⅝” chimney cap mesh.
But which size should you buy for your chimney cap?
In most cases, the standard ¾” mesh is your best bet. It’s open enough to facilitate a good draft, but it’s also tight enough to keep out wildlife and effectively arrest sparks.
If the law in your area requires it, though, a cap with ⅝” mesh may be your only choice. Even if they’re not required by law, these smaller-meshed caps are great spark arrestors and have a slight edge in the animal exclusion department. Just be sure your chimney still drafts properly if you opt for ⅝” mesh.
After mesh size, the next thing to consider is the size of your chimney cap itself. Which sizes are available, and which one will fit your chimney? Our chimney cap size guide covers everything you need to know to find the right size and ensure a perfect fit on your crown or flue.
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