The HY-C Guide to Multi-Flue Chimney Caps

For all their nuances and complexities, chimney caps have a pretty simple function: to keep wildlife and weather out of your chimney flue. Most chimney caps — the vast majority, in fact — attach directly to the chimney’s flue tile.

But what if you have two or more flues on the same chimney?

One solution is to put a standard single-flue chimney cap on each individual flue pipe. But for a cleaner, more efficient result, it’s possible to cover multiple chimney flues with one big cap. These caps are, fittingly, called multi-flue chimney caps.

But what sizes do these multi-flue caps come in? How do you install one? And what are they made of?

At HY-C, we manufacture dozens of styles of both single-flue and multi-flue chimney caps. In this guide, we’re going to focus on the multi-flue caps.

By the time you’re finished here, you’ll understand what materials these chimney caps are made from, which sizes they come in, how to install one, and whether or not getting one is right for you.

Table of Contents (click to jump to a section):

• Multi-Flue Chimney Cap Materials
• Multi-Flue Chimney Cap Sizes
• Multi-Flue Chimney Cap Installation

Multi-Flue Chimney Cap Materials

In order to stand up to weather and nuisance wildlife, chimney caps must be fabricated from metal. And while there are several types and alloys of metals out in the world, we use four kinds of metals in our multi-flue chimney caps:

• Aluminum
• Galvanized steel
• Stainless steel
• Copper

Aluminum is lightweight and relatively inexpensive. And while it may be a little lighter on your wallet, it's a bit light in the wildlife protection department, too. Critters like squirrels and raccoons can chew right through aluminum and get access to your flue.

If you’re looking for something a little bit stronger, steel is a good option. Galvanized steel is cost-effective while still maintaining a great level of wildlife-resistance. Stainless steel, on the other hand, is about as strong a chimney cap material as you’ll find. It carries a higher price tag as a result.

Finally, the least-common multi-flue chimney cap material is copper. It offers a level of weather and wildlife protection somewhere between aluminum and galvanized steel. Its relative rarity and eye-catching finish mean copper chimney caps command a sky-high price.

Multi-Flue Chimney Cap Sizes

Single-flue chimney cap sizing is easy. All you have to do is measure the outside dimensions of your flue pipe (e.g., 13” x 13”) and find a cap with the same dimensions. Because a single-flue chimney cap attaches directly to the flue, the size of the flue determines the size of the cap.

Multi-flue chimney caps, on the other hand, attach directly to your chimney’s crown — the concrete top that the flue pipe protrudes from. This means the dimensions of the crown determine the dimensions of the chimney cap you’ll need.

It’s helpful to keep two measurements in mind when looking for a multi-flue chimney cap:

• The screen-to-screen measurement
• The height of the chimney cap

Screen-to-Screen Measurements

Screen-to-screen measurements are easy enough to understand. Essentially, they’re the length and width of a multi-flue chimney cap. Our stock selection of multi-flue chimney caps come in 17 unique screen-to-screen dimensions:

• 10” x 10”
• 10” x 14”
• 13” x 19”
• 14” x 14”
• 17” x 17”
• 14” x 21”
• 14” x 26”
• 14” x 30”
• 14” x 34”
• 15” x 37”
• 17” x 29”
• 17” x 35”
• 17” x 41”
• 17” x 49”
• 17” x 53”
• 17” x 58”
• 17” x 64”

There’s another factor to consider, though: the flange. A multi-flue chimney cap’s flange extends 1-¼” perpendicularly from the bottom of the screen.

The flange adds 2-½” to the screen-to-screen length and width of a multi-flue chimney cap (because there’s a 1-¼” flange on each side of the cap). So, a multi-flue cap with a screen-to-screen measurement of 17” x 41” has an actual length and width of 19-½” x 43-½”. This is true for all of our stock multi-flue caps:

This distinction between screen-to-screen and flange-to-flange dimensions will come in handy in a bit when we talk about installation.

Height

In order for a chimney to draft correctly, your chimney cap needs to be high enough above the flue not to interfere with the airflow. If a chimney cap is too close to a flue opening, your flue will draw slowly, potentially causing smoke to back up into your home.

For this reason, it’s vital that the hood of your chimney cap be at least 5” above your flue. To ensure these safe distances are met, we make our multi-flue chimney caps in different heights: 8 inches, 10 inches, and 14 inches.

Say your flue protrudes 5 inches from your chimney crown. If you were to add an 8-inch-high multi-flue chimney cap, you’d only be left with 3 inches of clearance — not enough to ensure a proper draw. In this instance, you’d need a 10-inch-high cap instead (for 5” of total clearance).

Multi-Flue Chimney Cap Installation

Multi-flue chimney caps install differently from single-flue caps. While single-flue caps attach directly to the chimney flue tile itself, multi-flue caps attach directly to the chimney crown. That means you need to know the length and width of your chimney crown to find the right-sized cap.

Let’s imagine we have a chimney cap with a screen-to-screen measurement of 17” x 41”. As you know, the flanges on the cap add 2-½” to the total length and width. That means this cap — from flange to flange — measures 19-½” x 43-½”.

So, this particular cap can fit a 19-½” x 43-½” chimney crown, right? Not quite. One of the most important parts of ensuring your chimney crown remains undamaged is leaving at least 1” of room around the edge of the chimney cap’s flanges. So the crown in our example needs to be at least 20-½” in width and 44-½” in length.

Let’s go through this the opposite way. Say you measure your chimney’s crown, and it comes out to 17-½” x 33-½”. You need to leave at least 1” around the edge of the crown, so you need a cap with flange-to-flange dimensions of 16-½” x 32-½” (or screen-to-screen dimensions of 14” x 30”). As it happens, we make a chimney cap with those dimensions.

You can find our multi-flue chimney cap sizes and the crown sizes they fit on our multi-flue chimney cap product pages.

Should You Get a Multi-Flue Chimney Cap?

Multi-flue chimney caps are complicated. Their sizing can be a bit confusing, they’re hard to get up onto a roof, and they can potentially make access for chimney cleaning difficult, too.

But if you have two or more flues on your chimney, you’ll be hard pressed to find a more all-inclusive, aesthetically pleasing chimney solution than a multi-flue cap.

If you need assistance finding the right one, don’t hesitate to get in touch with our customer service team. They’ll be happy to assist you with sizing, material selection, installation tips, and more. And, if you’re ready to find a multi-flue chimney cap of your own, use the product locator below!