Masonry Magazine December 2009 Page. 20
CHIMNEYS & FIREPLACES
Installing the Correct Chimney Cap
BY JOSEPH BURNS
A chimney cap is the least-expensive preventative measure one can take to protect a chimney from deterioration and keep it operating properly. The benefits of a properly sized and installed cap include keeping out weather, such as rain and snow, and animals, such as raccoons and birds. A devious raccoon entering through an open chimney can cause immeasurable damage to the interior of a home.
The uncovered chimney that allows rain and snow to enter eventually will deteriorate and, ultimately, will deem the chimney unsafe to use until costly repairs are made. Additionally, a cap can prevent downdrafts while the fireplace is in use, making the fire burn more safely and efficiently.
There are many options to choose from when deciding which type of professional grade chimney cap to install, from both a performance standpoint and an aesthetic preference. Codes dictate the screen or mesh opening dimensions, depending on where in the country it is installed.
For example, a cap with a screen opening of 5/8-inch is required in most of California and parts of Nevada, because it will serve as a better spark arrestor in these areas where wild fires are a major concern. In most other areas of the country, a 3/4-inch mesh is used, because it is less likely to become clogged up with soot or ice. Another performance factor to keep in mind is that codes dictate a minimum of eight inches of clearance height between termination of the chimney and the bottom of the chimney cap lid to prevent restriction of the flue gasses.
Chimney caps can be mounted in different ways. A "crown mounted" chimney cap is used when covering multiple flues with a single cap, or when no flue tile extends from the crown of the chimney to mount a cap. The caps are designed to mount directly to the crown or brick portion of the chimney, and masonry screws are used to fasten directly to the crown.
Alternatively, a "single flue" mounted cap is installed when there is extending clay flue tile protruding from the crown of the chimney. The cap is made with a frame that fits directly over the flue tile and is fastened with friction screws to the side of the flue tile. An important thing to consider in this situation is the distance between flue tiles, in the event multiple caps are being installed. There are typically at least 3.5 inches of overhang on each lid, so at least seven inches of space needs to exist between flues. If there is less space, a crown mount cap will be needed.
Aesthetically, homeowners can choose from caps made from stainless steel, which usually carry a lifetime warranty, or galvanized steel, which are typically painted black but only carry a limited warranty. Copper is another common material used to dress up the appearance of the chimney, but it comes at a premium price point.