How to Measure and Install a Chimney Cap Correctly

Last Updated on by Jay Green

It’s not very difficult to choose exactly the right chimney cap for your home, especially if you take it one step at a time.  There are just four things to consider:

  1. shape
  2. type
  3. metal
  4. and size.

First, what shape should your chimney cap be?

Look at your chimney and find the flue, the pipe that lets the smoke out.  It’s either round, square or rectangular.
If you have more than one flue in your chimney, the arrangement of flues is rectangular.

So if your flue is rectangular, or if you have more than one flue, consider the shape you need to be rectangular. (For now, we’re just talking about masonry or brick chimneys with tile flues. We’ll talk about metal chimneys later.)

Round Flue

Round Flue without a Chimney Cap.

Square Flue without a Chimney Cap

This is a Rectangular arrangement.
Rectangular arrangement of flues requiring a Rectangular Shape for your Chimney Cap.


OK, now let’s figure out which type of chimney cap you need.
If your flue sticks up above your
chimney crown (the concrete pad
surrounding the flue) and is a square or
a small rectangular one, you can
use a single flue chimney cap that
attaches to the outside of the flue
with set screws.You can use an outside mount chimney
cap to cover your entire chimney.  These
are usually custom made due to variation
in chimney dimensions.
If your flue sticks up above the chimney
crown less than one inch, you need a
top mount cap. Top mount chimney caps
are installed with screws through a flange
that rests on the chimney crown.If you have more than one flue, you have a choice. One option is to use an single flue chimney cap on each individual flue.  This only works if you have adequate space between the flues. The usual choice
is to use a single top mount chimney cap that covers all of the flues, as in the illustration to the right.Round outside mount chimney caps fit around the outside of a round flue, whereas sleeve fit chimney caps fit inside round flues.You can see examples of each type below:
Below are Examples of Outside Mount Chimney Caps:
Click on any photo to find out more.
Round, single-flue clamp shimney cap.
Gelco single-flue, stainless steel outside mount chimney cap. Masonry round chimney cap by Chim Cap
Copper single-flue clamp chimney cap.
Below are Examples of Top Mount Chimney Caps:
Click on any photo to find out more.
Copper top mount chimney cap from Whitecaps with large lid
Gelco Model C galvanized top mount chimney cap Gelco Model C copper top mount chimney cap
Below are Examples of Sleeve Fit Chimney Caps:
Click on any photo to find out more.
sleeve fit galvanized chimney cap Weatherseal solid pack chimney cap
Vacu Stack chimney cap, sleeve fit
Now that you know what shape and what type of chimney cap you need, it’s time to consider which metal would be best for your chimney cap.
Chimney caps are manufactured from stainless steel, copper, and 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 usually come with a lifetime warranty. Some companies can have stainless steel caps coated with black or colored heat resistant coatings. Galvanized steel is the least expensive and the least durable.   Galvanized steel chimney caps are usually painted black.

Copper is not recommended for light colored chimneys.  Stainless steel is the preferred metal for salt water climates.

Click on any photo
to learn more.
Stainless Steel
Gelco copper chimney caps
Copper single-flue clamp chimney cap.
HomeSaver Pro round stainless steel chimney cap
HomeSaver Pro stainless steel outside mount chimney cap
Gelco single flue galvanized outside mount chimney cap
HomeSaver Pro galvanized round chimney cap
Finally, what size should your chimney cap be?
To answer this question you or a contractor will have to get up on the roof and take careful measurements. Be sure to take a pencil and paper, as well as a metal yardstick or metal tape measure.  Take a metal square to insure you are measuring with square, 90 degree, corners.

If you have a square or rectangular clay flue pipe that sticks up above the chimney crown more than an inch, measure and write down the length and the width of the flue.

If you have a round clay flue, measure its outside diameter.

If your flue doesn’t stick up at least an inch, or if you have multiple flues, measure each side of the area you want the chimney cap to cover.   Start with the longest side and, going clockwise, measure each side of the flue or array of flues. Be sure you are using 90 degree corners.  Record your measurements in inches.

If you plan to use a top mount chimney cap, there must be at least 5 inches of clearance between the top of your flue and the lid (or roof) of the chimney cap. The distance from the chimney crown to a point 5 inches above the tallest flue is called “screen height.”

Now is the time to consider whether you want a chimney cap or if what you really need is a combination damper and chimney cap. We recommend the Lyemance brand of dampers because they save you up to 90 percent of the energy that is lost with a traditional damper. The Lyemance dampers are available in combination with a quality chimney cap.
Chimney caps for unusual conditions.
Some chimneys whistle or sing in high winds; some don’t draw well when the wind is coming from certain directions; and some don’t draw at all.Please email us to let us know if you need a chimney cap that rotates so that its open side is always down wind. We can arrange that for you.Other chimney caps are made to cure ‘back-puffing’ from down currents caused by mountains or tall buildings. These are available both for round flues and for masonry flues.  For the most difficult cases, there are chimney caps with integral electric fans that pull the smoke out of the chimney.  Likewise, these Exhausto Fans are available for round fluesand for other flues.
A special note about metal chimneys for gas fireplaces and woodstoves.
Metal chimneys come in three types:  just plain pipe, air insulated, and solid pack (also called ‘Class A’ chimneys).
Plain pipe is just that: it’s typically found on woodstoves.Chim Cap round chimney capJust measure the inside diameter of the pipe and order a chimney cap of the same diameter. (A chimney cap labeled ‘8 inch’ will fit tightly inside an 8 inch flue.)

Air insulated flWeathershield air insulated chimney capues have an air jacket surrounding the flue, a pipe within a pipe.  Some have a larger third jacket that’s just for appearance.  Choose a chimney cap designated for air insulated chimneys, one that fits inside the flue and has a bottom plate large enough to cover the air jacket and decorative jacket, if one is present.

Solid pack flues have a flue surrounded by packed insulation and an outer pipe.  A third decorative pipe may or may not be present. ChooseHomeSaverPro Guardian chimney cap  a chimney cap designated for solid pack chimneys, one that fits inside the flue and has a bottom plate large enough to cover the outer jacket and decorative jacket, if one is present.

A special note about custom chimney caps.

Sometimes, the chimney cap you want just doesn’t exist as a stock item.

Gelco copper Custom Chimney Cap with hip ridge top.Gelco stainless steel Custom Chimney Cap with Cone lid.Gelco galvanized custom order cross-shaped chimney cap.Gelco galvanized custom order T-shaped chimney cap.
Maybe you want something special, such as a chimney cap with a hip, conical, or other interesting top.  Maybe you want a non-standard shape, such as a
T-shaped chimney cap.  A custom chimney cap may best serve your needs. We specialize in custom chimney caps and are always available to be of assistance to you if you need help with this.  Email us or call us at
703-795-2401, and we will be glad to assist you with your custom chimney cap.Because custom made caps are one-of-a-kind, they cannot be returned for a refund.  For this reason, and because they are more expensive than standard caps, it is essential to measure carefully.  Write down the longest side first, then each successive side going clockwise.  Be sure to measure for screen height (from chimney crown to the top of the tallest flue, plus five inches.)
A special note about chimney caps for California and other areas requiring 5/8″ mesh

“Mesh” refers to the screened area of chimney caps.

Many localities–primarily California, but also some other areas around the country–have codes calling for 1/2″ spark arrestors. Some localities call for such spark arrestors in “wooded areas” or “within 200 feet of wooded areas.” According to the National Fire Protection Association, chimney caps with 5/8″ mesh will not allow a 1/2″ sphere through them, and thus are considered the industry standard for California-sized chimney caps. If you live in such an area, local laws may require such specially sized mesh to conform to these spark arrestor codes.  We have a wide selection of chimney caps with 5/8″ mesh for round, top mount, outside mount, single and multi-flues.

Chimney Caps with 3/4 Inch Mesh or
Chimney Caps with 5/8 Inch Mesh:
What’s the Difference?
© 2006 PennVentures LLC

Is there a difference between chimney caps with 3/4″ mesh and chimney caps with 5/8″ mesh?  Is it a difference I need to know about before I select a chimney cap?

Yes, there is a difference between 3/4″ and 5/8″ mesh chimney caps, and, depending on where you live or other special circumstances, it might be a difference you need to take into account when buying your chimney cap.

The “mesh” is the screen part of the chimney cap.  It is the section below the “lid” or roof that lets the gases out of your chimney but keeps leaves and birds, insects, and other animals from getting into your home. The two mesh sizes for chimney caps are 3/4″ or 5/8″, with the 3/4″ mesh having slightly larger holes in the screen than the 5/8″ mesh has.

The vast majority of American chimney caps have 3/4″ mesh.  But many localities — primarily California, but also some in other areas around the country — have building codes that call for chimney caps with “1/2 inch spark arrestors.” Some localities call for such chimney caps in wooded areas or within 200 feet of wooded areas. The purpose of chimney caps with “1/2 inchspark arrestors” is to prevent sparks and burning detritus that are a half inch or larger from escaping from chimney caps and starting wild fires.

So what are chimney caps with “1/2 inch spark arrestors”? According to the National Fire Protection Association, chimney caps with 5/8″ mesh will not allow a half-inch sphere through them. Chimney caps with 5/8″ mesh, therefore, are considered the industry standard for all localities that require chimney caps with “1/2 inch spark arrestors.”

Since so many of the chimney caps with the smaller, 5/8″ mesh are used in California, chimney caps with the 5/8″ mesh are also often called California-style chimney caps.

How will I know if I need a California style, 5/8″ mesh chimney cap? If you are buying a home, ask the realtor.  If you already own the home, you can call the local government department that deals with building codes such as the department that issues building permits. You local chimney sweep will also know.

Would I ever want California style, 5/8″ mesh chimney caps if my local building codes don’t require them? Yes, some people select chimney caps with 5/8″ mesh even though they are not required by their locality.  People who have wooden roofs on their home or outbuildings, those with woods near their homes, and others who live in dry areas that are susceptible to wild fires have chosen to buy chimney caps with 5/8″ mesh to reduce the likelihood that a spark escaping from their chimney cap could start an outside fire.

There’s one other reason people might select chimney caps with 5/8″ mesh.  If you have an oval flue and want a chimney cap that mounts to the flue instead of to the crown of your chimney, consider a 5/8″ mesh chimney cap.  It is not unusual for homes in California, Arizona, Nevada, and Oregon to have oval flues, so some chimney cap manufacturers make 5/8″ mesh chimney caps with a special base that can fit either a rectangular flue or an oval flue.

Chimney caps with 5/8″ mesh are manufactured to meet local building codes designed to reduce wild fires. But you might have a special circumstance, such as a roof or exterior environment susceptible to fire, which might lead you to select such a chimney cap even if your local codes do not require 5/8″ mesh chimney caps.

Quick and Easy Selection Guide Table for
Chimney Caps for Round Flues
© 2004, 2005 PennVentures LLC
Types of
Chimney Caps for Round Flues
Stainless Steel
Chimney Cap
Chimney Cap
Chimney Cap for Air-Insulated Flues Chimney Cap for Solid-Packed Flues Clay Flues Cap for Metal Liners Cap for Stove Pipes Chimney Cap for Flexible Relining Systems  Chimney Cap for Wood-burning Stoves & Inserts Chimney
Cap for Draft Problems
Large selection of chimney caps including this HomeSaver Pro Stainless Steel round Guardian Cap.

HomeSaver Pro Guardian

Large selection of chimney caps including this HomeSaver Pro Stainless Steel Round Chimney Cap.

HomeSaver Pro

Large selection of chimney caps including this HomeSaver Pro Galvanized Round Chimney Cap.

HomeSaver Pro


Chim Cap
Forever Round™

Large selection of chimney caps including this Chim Cap Stainless Steel Forever Round Chimney Cap.

Chim Cap
Forever Round™

Large selection of chimney caps including this Vacu-Stack Stainless Steel Round Cap.


Not UL Listed

Not UL Listed

Large selection of chimney caps including this Exhausto Fans, a combination exhaust fan and chimney cap.
Exhausto Fans
(combination exhaust fan and chimney cap)

and cast aluminum
Not UL Listed

Not UL Listed


double or triple walled


double or triple walled

with exposed insulation



Not UL Listed

Not UL Listed

European Copper Chimney Pots

Use this quick and easy Selection Guide Table to help you pick the Chimney Cap best suited to the type of round flue you have and any special conditions, such as drafting problems,
your fireplace or chimney has.

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