Does your chimney need a cap?
Metal Chimneys - Masonry Chimneys - Caps with integral dampers - Custom Caps - Electric Draft Increasing caps
The various claims made by chimney sweeps, cap manufacturers and fireplace retailers can often confuse the issue. In this article we'll take an in-depth look at the different types of chimney caps and answer this burning question once and for all.
Metal chimneys are used for many wood stove and pre-fab fireplace installations, as well as in gas venting. Most all metal chimneys need to have a cap or termination. This is for a number of reasons including:
1. There is nowhere for rain to go in these chimneys. Without a cap, the rain will run into your stove, fireplace or heater and/or ruin your walls and ceilings.
2. Birds and other animals will enjoy the warmth of your chimney and possibly clog it with nests. The cap helps keep them out.
3. Metal chimneys are made of two or three layers of metal with air or insulation between them. Without a cap, water and moisture can get into these layers and cause premature failure of the chimney and other problems.
Most metal chimneys are sold and installed with a termination cap that is manufactured by the maker of the chimney parts. This is often the best and safest cap to use because it is designed specifically for the exact brand. There are times when you may need to install a generic retrofit onto a metal chimney, such as when:
1. You have draft or wind problems.
2. Your cap has worn out and you cannot locate the manufacturer of your chimney.
If you have draft problems you can use "draft increasing" or vacuum chimney caps which are designed to use the wind to create a stronger updraft.
Manufacturers of these caps include:
Artis at: http://www.artiscaps.com/chimney.html
Please check with the manufacturers and your chimney professional to determine if these devices will work on your metal chimney.
If you don't have draft problems and just need a replacement cap, first try to find the same brand as the existing termination. If that fails, you can often use a cap from a similar brand, but make certain you confirm this with the store where you are purchasing. Another option is a "generic" metal chimney termination such as the WeatherShield at:
Note: Some metal chimneys are "air cooled" by venting that is on the top. If your chimney is of this type, be certain not to close off the venting slots on the top. A HOUSE FIRE COULD RESULT FROM CLOSING THESE VENTILATION SLOTS!
Special caps are available for these chimneys to assure proper cooling. Check the WeatherShield link above for information about a model (WSA TDW) with this feature.
Masonry Chimneys and Fireplaces
There are advantages and disadvantages of capping a masonry chimney or fireplace. Let's list negative and positive points and then we'll discuss the different models that are available.
1. Draft Restriction - An improperly designed or installed chimney cap can possibly reduce the draft of a chimney.
2. Clogging of Screen in Cap - Some chimney caps have small screening which can become clogged with soot and creosote after heavy use. This will cause draft reductions and poor performance of your stove/fireplace.
3. Discoloration of chimney exterior - In some cases, creosote and tar can collect on the chimney cap and then run down the outside of the chimney structure. This can discolor the stucco or brick. This is usually a problem only with older woodstoves and/or the use of green (unseasoned) wood.
4. Replacement/Reinstallation - Chimney caps can blow off in high winds. This can destroy the cap or at the very least require another trip on top of the home to reinstall it.
1. Keeps Animals, especially Raccoons and Birds, from setting up home in your chimney or fireplace.
2. Keeps Rain and moisture from building up inside chimney. This can help reduce the chimney smell that often invades homes in the warmer weather.
3. Sheds ice and rain from the chimney crown, which is the cement cover on the top of the chimney structure. This will extend the life of the crown and eliminate some causes of cracking of the flue tile.
4. Increase draft of chimney, especially in areas with constant wind.
Note about chimney sizes - The three most popular sizes for masonry chimneys are 8" x 8", 8" x 12" and 12" x 12". Many other stock sizes are available. Custom sizes and styles are also produced by many manufacturers.
Cap Types for Masonry Flues
Standard Cap with screen - Black or Stainless Steel Draft Increasing Caps Caps with integral Damper Mechanisms Custom Caps - Metal and Masonry
Standard caps are made from a number of materials including steel, stainless steel, copper or aluminum. The most popular styles are stainless steel and black painted steel. Most models feature side screening which keeps most birds and small animals out of the chimney and also keeps larger sparks from existing the chimney.
These caps are mounted onto the chimney in various ways, the most popular being screws which are spaced around the base angle of the cap and tightened against the flue tile. If the chimney is unlined or the flue does not protrude far enough out the top, inside mounting models can be used. If neither of these methods work, manufacturers also provide mounting angles or other fasteners which can be lag bolted or cemented down to theta of the chimney structure.
Standard Stainless Cap
Stainless Steel is a preferable material since it can better handle constant exposure to rain, wind, smoke and the other nasty conditions on top of your chimney. It also is less susceptible to rust, which will reduce the chance of getting stains on your chimney from cap runoff. Example caps at:
According to wind tunnel studies, standard caps have good properties for increasing draft in windy situations. In fact, standard caps can often function as well as, if not better than, certain models marketed as "draft increasing".
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