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Custom Chimney Caps: Do You Need One?

September 25th, 2023 | 6 min. read

By Louis Greubel

HY-C employees on the factory floor working on building a custom chimney cap.

A chimney cap serves a humble role. It sits securely atop your chimney, keeping out rain, hail, snow, and even critters. It does its job passively but unceasingly, its sturdy metal frame bolted tightly onto your chimney, braving the elements season after season.

Most people don’t think or know much about their chimney cap. After all, they can last well over 50 years, and homeowners generally only have to consider them in a select few circumstances:

  1. When building a new home
  2. After a problem is discovered with their existing cap
  3. When replacing a cap purely for aesthetic reasons

Because they’re the type of thing you don’t buy often, people tend to have a lot of questions about chimney caps when they actually do have to think about them. One of the most important ones to consider while shopping around is, “Can I buy a standard chimney cap, or do I need a custom-made chimney cap?

Well, we’ve been making chimney caps at HY-C for over 75 years. In fact, our factory floor is no more than a few yards from where this very article is being written. We make a few dependable lines of standard caps, and we also take custom chimney cap orders all the time. We know how to make them, who needs them, and everything in between. And we want to teach you all about it.

In this guide, we’ll cover everything you need to know about chimney cap sizes. Whether you’re looking for a 5” x 9” rectangular single-flue cap or a multi-flue custom-skirt copper cap, by the time you’re done, you’ll know how chimney cap sizing works, and you’ll understand whether or not you need a custom chimney cap on your home.

Which Standard Sizes Do Chimney Caps Come In?

Think about chimney cap sizes like shoe sizes: when you shop for shoes, do you expect to have to special order them? Probably not — shoes are made in specific, incremental sizes, and unless you have especially small or big feet, the standard sizes will probably work for you.

Chimney caps basically work the same way. Manufacturers make chimney caps in very particular sizes, and we do that because those standard sizes fit most chimney flues around the country. In fact, one of our company owners estimates that 90% to 95% of the chimney caps we sell are standard-sized caps.

Put simply, the only situation in which you’ll need a custom-made chimney cap (outside of aesthetic reasons) is when your chimney flue or crown doesn’t fit within the standard flue or crown size ranges. So in order to understand whether you need a custom cap or not, learning about the standard sizes is a great place to start.

Chimney caps fall into one of four categories:

  1. Single-flue square/rectangular bolt-on
  2. Single-flue round bolt-on
  3. Single-flue round slip-in
  4. Multi-flue

Each type of chimney cap has its own size range, and it’s very likely that your chimney flue (or crown, in the case of a multi-flue cap) falls within the standard size ranges.

Single-Flue Square or Rectangular Bolt-On Chimney Cap Sizes

HY-C Square Bolt-on Chimney Cap

The bulk of the chimney caps on the market connect directly to your flue tile (the brown pipe that protrudes from the concrete chimney crown). They make this connection one of two ways: they bolt onto the tile or they slip into the tile.

Square or rectangular chimney caps designed to bolt onto a single, square- or rectangular-shaped flue come in a range of sizes. The following table contains standard chimney cap dimensions and the flue sizes on which they fit.

If you have a square or rectangular flue whose dimensions are within the following range, you don’t need a custom chimney cap:

Flues with dimensions between… Need a cap with dimensions of…
3.5″ x 7.5″ to 5.5″ x 9.5″ 5″ x 9″
7.5″ x 7.5″ to 9.5″ x 9.5″ 9″ x 9″
7.5″ x 11.5″ to 9.5″ x 13.5″ 9″ x 13″
7.5″ x 16.5″ to 9.25″ x 18.25″ 9″ x 18″
9.75″ x 9.75″ to 12″ x 12″ 11″ x 11″
10″ x 14″ to 12.5″ x 16.25″ 12″ x 16″
11.5″ x 11.5″ to 13.5″ x 13.5″ 13″ x 13″
11.5″ x 16.5″ to 13.25″ x 18.25″ 13″ x 18″
13.75″ x 13.75″ to 16″ x 16″ 15″ x 15″
16.5″ x 16.5″ to 18″ x 18″ 18″ x 18″
18.5″ x 18.5″ to 20.25″ x 20.25″ 20″ x 20″

Single-Flue Round Bolt-On Chimney Cap Sizes

HY-C Round Bolt-on Chimney Cap

If your chimney flue is round instead of square or rectangular, don’t worry — there are standard chimney caps for you as well. Instead of length and width measurements, though, the cap you need will depend on the diameter of your chimney flue.

The table below will help you to find the chimney cap diameter you need based on the diameter of your round chimney flue. If your flue is within this range, you don’t need a custom chimney cap:

Flues with diameters between… Need a cap with a diameter of…
9.5″ to 10.5″ 10″
11.5″ to 12.5″ 12″
13.5″ to 14.5″ 14″
15.5″ to 16.5″ 16″
17.5″ to 18.5″ 18″

Single-Flue Round Slip-In Chimney Cap Sizes

HY-C Square Bolt-on Chimney Cap

Not all customers want or need a bolt-on chimney cap. For this reason, manufacturers design round caps that slip into the chimney flue instead of being bolted on. The installation process is much easier; you just slide the legs of the cap into the flue, and they’re held in place by tension.

Despite the installation method varying, round slip-in caps essentially fit the same flue sizes as round bolt-on caps (with one additional smaller size available). If your flue has a diameter within this range, you don’t need a custom chimney cap:

Flues with diameters between… Need a cap with a diameter of…
7.5″ to 8.5″ 8″
9.5″ to 10.5″ 10″
11.5″ to 12.5″ 12″
13.5″ to 14.5″ 14″
15.5″ to 16.5″ 16″
17.5″ to 18.5″ 18″

Multi-Flue Chimney Cap Sizes

A Draft King Big Top Black Galvanized Steel Multi-Flue Chimney Cap installed on a multi-flue chimney. The home's yard can be seen in the background.

Multi-flue chimney caps are quite a bit different than single-flue caps. Installers screw these caps directly into the chimney’s crown — the concrete slab poured on top of the masonry and around the flue tiles.

These caps are measured in screen-to-screen dimensions, but it’s important to note that they come with flanges on all four sides of them — metal edges that are perpendicular to the chimney cap’s mesh screen.

The flanges on our multi-flue chimney caps come with pre-drilled holes to make them easier to install. The flanges themselves measure 1.25 inches, meaning they add a total of 2.5 inches to the screen-to-screen length and screen-to-screen width of the cap (since there are two on each side).


Close-up of a multi-flue chimney cap flange

The following table lays out both the screen-to-screen and flange-to-flange dimensions of our multi-flue chimney caps. If the dimensions of your multi-flue chimney’s crown fall within any of the ranges on the table, you don’t need a custom chimney cap:

Crowns with dimensions between… Need a cap with flange-to-flange dimensions of… Cap’s screen-to-screen measurement (for reference)
14.5″ x 14.5″ to 15″ x 15″ 12.5″ x 12.5″ 10″ x 10″
14.5″ x 18.5″ to 15″ x 19″ 12.5″ x 16.5″ 10″ x 14″
17.5″ x 23.5″ to 18″ x 24″ 15.5″ x 21.5″ 13″ x 19″
18.5″ x 18.5″ to 19″ x 19″ 16.5″ x 16.5″ 14″ x 14″
21.5″ x 21.5″ to 22″ x 22″ 19.5″ x 19.5″ 17″ x 17″
18.5″ x 25.5″ to 19″ x 26″ 16.5″ x 23.5″ 14″ x 21″
18.5″ x 30.5″ to 19″ x 31″ 16.5″ x 28.5″ 14″ x 26″
18.5″ x 34.5″ to 19″ x 35″ 16.5″ x 32.5″ 14″ x 30″
18.5″ x 38.5″ to 19″ x 39″ 16.5″ x 36.5″ 14″ x 34″
19.5″ x 41.5″ to 20″ x 42″ 17.5″ x 39.5″ 15″ x 37″
21.5″ x 34.5″ to 22″ x 35″ 19.5″ x 32.5″ 17″ x 29″
21.5″ x 39.5″ to 22″ x 40″ 19.5″ x 37.5″ 17″ x 35″
21.5″ x 45.5″ to 22″ x 46″ 19.5″ x 43.5″ 17″ x 41″
21.5″ x 53.5″ to 22″ x 54″ 19.5″ x 51.5″ 17″ x 49″
21.5″ x 57.5″ to 22″ x 58″ 19.5″ x 55.5″ 17″ x 53″
21.5″ x 62.5″ to 22″ x 63″ 19.5″ x 60.5″ 17″ x 58″
21.5″ x 68.5″ to 22″ x 69″ 19.5″ x 66.5″ 17″ x 64″

What if Your Chimney Falls Outside the Standard Size Ranges?

Before now, you probably knew very little about chimney caps, let alone how to measure one. As you can tell, though, it’s pretty easy: just figure out which one of the four categories your chimney falls into, and check to see whether or not its dimensions can accommodate a standard chimney cap. If you’re like 90% to 95% of people out there, a standard cap will work for you.

If your flue or crown falls outside of the standard dimensions, though, you’ll probably need to purchase a custom chimney cap. If that’s the case, you’re in luck: we make custom-sized chimney caps all the time.

Wondering how to get started? Our customer service team can help you figure out what style, color, and dimensions you’ll need for your custom chimney cap based on your current chimney flue or crown. Reach out today to find the perfect chimney cap for your home.

Louis Greubel

Louis earned a bachelor's degree in English with a focus in rhetoric and composition from St. Louis University in 2017. He has worked in marketing as a content writer for over 5 years. Currently, he oversees the HY-C Learning Center, helping HY-C subject matter experts to share their decades of home solution products experience with homeowners and sales partners across the country.


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