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