by Tom


by Tom


Top Mount Chimney Cap Measure Guide

How to Measure for a Top Mounted Chimney Cap:
Top Mount Chimney Cap Measure Guide for Chimney Caps that Attach to the Crown


Top Mount Chimney Caps (typically used with multiple flues but also used with chimneys with a single flue) mount on the concrete crown of the chimney.  They can also be used if you have only one flue on the chimney.

You can attach a top mount chimney cap either with 1/4” Tapcon screws (using a 3/16″ Tapcon drill bit) that go through pre-drilled holes in the chimney cap flanges and then into the crown, or you can attach it with Construction Adhesive that affixes the chimney cap flanges to the cement crown.

Top mount chimney caps attach to the chimney crown with flanges.

Whether you are using a top mount chimney cap for one or more flues, here’s how to measure for and select the right chimney cap to fit:

What to Measure for a Top Mount Chimney Cap

You need to take three measurements in order to choose the correct top mount chimney cap.

•     First, measure the length and width of your entire chimney, as shown by the red dotted line in the diagram below.

•     Next, measure the length and width of a rectangle just big enough to include all the flues on your chimney, as shown by the black dotted line. This is the minimum screen size.

Multi Flue Chimney Caps - Measure for Size

•     Last, measure the height of the tallest flue above the top of the chimney, as shown by the blue dotted line .

Multi Flue Chimney Caps - Measure for Height

Your chimney cap can be any screen size between the dotted red rectangle and the dotted black rectangle.

Most chimney caps have mounting flanges that add 1 1/2 inches to each side of the screen. So, for example, a top mounting chimney cap with a screen size of 13 by 17 inches will cover 16 by 20 inches of the top of your chimney. Some top-mount chimney caps can be installed with the mounting flanges inside the screen (facing toward the flues) or outside of it (facing toward the edges of the chimney.)

•     If your goal is to protect the top of your chimney from deterioration caused by weather and acid rain, choose the largest screen size that will fit within the red dotted line.

•     If your goal is to be as economical as possible, select a chimney cap the size of the black dotted line.

•     If your goal is to get the maximum protection for the top of your chimney for the minimum price, select a chimney cap size midway between the red and black dotted lines.

Some chimney caps are taller than others. The height of the screen part of a chimney cap is the screen height. There must be at least 5 inches of clearance between the top of your tallest flue and the lid (or roof) of the chimney cap. Select a chimney cap with a screen height 5 inches above your tallest flue (at least 5 inches taller than the blue dotted line.)


Which Metal is Best for a Top Mount or Multi-Flue Chimney Cap?

Multi-flue chimney caps are manufactured from stainless steel, copper, and black galvanized steel. Stainless steel is the best value for the dollar. Copper is the most elegant, especially for historic or upscale homes. Stainless steel and copper chimney caps come with a lifetime warranty. Some stainless steel top mount chimney caps can be powder coated with black or colored heat resistant finish. Galvanized steel is the least expensive and the least durable. Galvanized steel chimney caps are painted black.

A copper top mount chimney cap is not recommended for light colored chimneys. Stainless steel is the preferred metal for salt water climates due to its rust resistance.

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  1. […] least one inch and you want a chimney cap that mounts to the top crown on your chimney, follow the measuring directions for top mount chimney caps (also known as multi-flue chimney […]

  2. Tom Hahn November 18, 2016 at 8:35 PM - Reply

    I am trying to find out how high my chimney cap should be above the top of the chimney for proper draft. The top of my chimney measures five foot by seven foot and has six flues in it. I have six brick/mortar posts supporting a one inch thick stone cap. That stone cap is about ten inches above the highest flue. It looks nice and is well proportioned when looking from the ground up. The chimney is about 29 foot high and is 2 foot above the peak of the roof. Yes, below is a walk in fireplace. My problem is when I have a fire in the fireplace, we generally, at times, have smoke in the room. I was told I have to raise the top stone cap higher for proper draft. But no one can tell me how high??? Any Ideas. Looking for some type of formula.
    Thanks for any suggestions.

    • Tom September 4, 2017 at 1:08 PM - Reply

      It sounds, Tom, like your stone cap, being 10 inches above your tallest flue, is greater than the 5-inches minimum required. We suspect the problem is due to a mismatch between the size of your flue(s) and the fireplace opening (given that it is a walk in fireplace.) An Enervex chimney fan is your best solution. They are guaranteed to work; the fan adjusts to compensate for the lack of sufficient chimney draft.

  3. Mike T. September 25, 2018 at 1:18 PM - Reply

    Will it be bad to have a taller cap? The tallest of 2 flues on my chimney is 4″. So a 10″ cap would work for me, but would a 12″ or 14″ be better?

    • Tom October 12, 2018 at 6:27 PM - Reply

      Six inches taller than the tallest flue is a minimum for good draft. A taller chimney cap will cost more, but not necessarily give you a better draft for your flue.

  4. Tom P November 26, 2018 at 7:41 PM - Reply

    What happens if there is less than 5” of clearance between the cap and top of flue?

    • Tom December 31, 2022 at 5:39 PM - Reply

      Your flue may not properly draft, causing smoke gather in your home instead of exiting through the flue.

    • Tom January 4, 2023 at 10:34 PM - Reply

      Tom, if there is less than five inches of clearance between the top of the flue and the top of the chimney cap, your fireplace and chimney may not draft properly. Smoke can back-puff into your home instead of exiting up your flue.

  5. Carl April 5, 2019 at 8:39 AM - Reply

    What is the minimum height that the chimney cap should be from the roof

    • Tom January 4, 2023 at 10:32 PM - Reply

      There is no relevant minimum height that the chimney cap should be from your home’s roof. The height to measure is from the top of the cement pad atop the chimney to the top of the tallest extending flue. Add 5 inches to that height, and select a chimney cap with a screen that total height.

  6. roman olijnyk June 13, 2019 at 10:38 AM - Reply

    Is there an advantage to having a 14 inch cap rather than a 10 in cap? I am mostly concerned about rain.

    • Tom January 4, 2023 at 10:28 PM - Reply

      Roman, chimney caps come with different screen heights because some flues just barely rise above the top of the cement pad on top of the chimney; other flues may be several inches tall. You want to select a top-mount chimney cap 5 inches taller that the height of your tallest existing flue. More than five inches doesn’t gain you anything. And as you mentioned, if the screen is significantly taller than the flue, you increase the risk of wind-blown rain entering your flue.

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