Chimney Cap Sizes (Measurement Guide)

Picture this: wintertime, the snow is falling, you have the fire crackling, and there is an orange glow around your living room, but then suddenly, there is a sound coming from your fireplace, and then a loud, falling sound as debris and twigs and snow come cascading out your fireplace. You need a chimney cap to avoid that problem in the future.

Brick chimney with metal chimney cap on a black metal roof with skylight window and dormer window

Read on and find out more.

Are Chimney-Caps A Standard Size?

Chimney caps come in different shapes and sizes, so there is no definite size, although there are the “usuals” or more common sizes to use.

For masonry chimneys made of bricks or stones, the common dimensions are 8 by 8 inches or 8 by 13 centimeters for smaller chimneys. There are 13 by 13, 8 by 17, or 13 by 17 inches for bigger fireplaces’ chimneys. 

It’s essential to measure your caps because if they don’t fit perfectly, they might not be effective in doing the work. 

Standard Chimney Cap Size

13x13 inches chimney cap

The sole purpose of a chimney cap is to act as a covering on your flue to protect the fireplace. Aside from protecting your chimney from water from rain or snow, it also keeps the embers and sparks in the fireplace. Caps are usually made of weatherproof materials like steel or copper mesh. 

A corresponding chimney size will make the cap a perfect fit for every standard size. For typical 8 by 8 inches caps, it would fit a 6.25 by 8.5 inches flue size perfectly. There are also 8 by 13 inches caps that would fit flues 6.25 by 11.5 inches and 8.5 by 13.5 inches in dimensions. 

Bigger chimneys 11.5 by 11.5 inches or 13.5 by 13.5 inches in dimensions would require a cap with a size of 13×13 inches. Another is chimneys with sizes that range from 11 by 16.5 inches to 13.5 by 18.5 inches, which would need caps 13×17 inches in size. 

How Thick Should a Chimney-Cap Be?

Asphalt roof with masonry brick chimney

A cap should be 2 inches or 5 centimeters thick all over to work perfectly and be durable enough no matter the weather and wear and tear.

Aside from protecting the chimney from any water damage, caps also keep out twigs, leaves, and whatever trash the wind carries.

If dirt accumulates in the stack, it could lead to a blocked flue that could cause harm not only to your stack but also to your health. There could be an accumulation of carbon monoxide that could cause respiratory distress when breathing. 

How Tall Should a Chimney-Cap Be?

Chimney height

For a chimney cap to be effective it needs to be at least 8 inches or 20 centimeters above your chimney’s flue tiles that it will be covering.

You can even go longer than this but don’t go lower than 8 inches or 20 centimeters. Going lower might interfere with the workings of a chimney’s draft. The draft directs smoke out of the stack. 

What Size Chimney-Cap Do I Need?

The perfect cap is the one that has a close size to both the inside and outside measurements of your flue. Also, remember that your cap should be higher than the flue in order for the chimney to work as it should. 

How To Measure For A Chimney-Cap?

Various methods measure the perfect cap to fit your smoke stack. It all depends on what your chimney style is. The easiest by far is measuring a cap for a single-flue chimney. You only need to gauge your chimney’s outside length and width. 

Step. 1 The first step is measuring the length of your flue from top to bottom. You do that by measuring from the chimney crown to the flue on top. 

Step. 2 After that, measure the flue pipe diameter from the inside from one edge to the other. 

Step. 3 After measuring the inside, measure the outside of the flue pipe just like you did on the inside. 

Step. 4 Use the measurement to choose the best cap. The best cap will have a similar or relative size to the inside measurement of your flue pipe.

The cap will be close to the size of your flue, especially if you have an industrial flue that is usually made of a thinner material. 

If you have an oval flue extending to an oval chimney, you will need a top-mount-style cap. Measure for a cap by assessing the size of the length and width of the flue. 

If you have a flue that is not extended and is not high enough for a flue mount cap, you need to acquire a cap leg kit that will still allow you to use a flue mount cap for your chimney.

This leg kit will be attached to the insides of the flue. Although it requires more work, this type of cap will work best in windy places. 

Brick house with stone coated metal roof tile plastic windows rain gutter and modular chimneys with rain cap

There are chimneys with multiple flues; no matter how short or extended the vents are, it will require a top-mounted cap.

The tallest flue height is measured because your cap should be at least 5 inches or 13 centimeters higher than the tallest flue. 

Step 1. First, you need to measure the width and length from the top and bottom of all the flues. 

Step 2. Once everything is measured, measure the height of your biggest and tallest flue. 

Step 3. Now, measure the chimney’s top, its length, and width. 

Step. 4. After that, you can choose one for your flue. Remember to choose one a little bit taller than the tallest flue. 

Remember these things for a chimney cap size, and stay on the right track when considering a cap design. See more related content in our article about the types of chimney caps on this page.


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