Chimney Caps

Chimney Caps - by Craig Issod [email protected]

Does your chimney need a cap?

Article Index
Metal Chimneys - Masonry Chimneys
Caps with integral dampers - Custom Caps - Electric Draft Increasing caps - Extendaflue (flue Extensions w 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

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 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
Vacu-Stak: http://www.woodheat.com/icp/vacu-stack.html
Aerocowl - http://www.u-nova.com/zflex/aerocowl/aero1.htm

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: http://www.woodheat.com/icp/weather.html

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.

Possible Disadvantages:
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 screen 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.

Possible Advantages:
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

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.

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:
http://www.chimcapcorp.com/meshsingleflue.html

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".

Draft Increasing Caps

These are the same caps mentioned earlier in this article for use with metal chimneys. The manufacturers also make adapters which allow use on masonry chimneys. When considering a draft increasing cap for bout chimney, keep the following point in mind:

Some draft increasing caps cut down on the effective cross sectional area of the chimney. This may have less importance if you have a stove hooked up to the fireplace, but might cause problems with an open fire.
Do not use mechanical caps which rely on spinning turbines or windvanes. The smoke and creosote from your stoves or fireplace will quickly gum up the workings of such caps.

Caps with integral Damper Mechanisms

Older fireplaces often have missing or loose-fitting damper mechanisms. This can result in wasted energy as well as a cold draft in the home when the fireplace is not in use. In these cases, the answer is often a top-sealing damper, which can easily be retrofitted to the chimney top. These dampers are avaialble with an integral cap. The damper is controlled by means of a cable which runs down inside the flue and is activated with a lever on the fireplace wall. Two well known manufacturers of these damper/cap combinations are:
CHIM-A-LATOR
LYEMANCE

Custom Caps

Many cap manufacturers also produce custom caps to fit odd-sized flues or multiple flues. You can also find custom caps in copper, brass, aluminum and other finishes which compliment the style of your chimney structure.
Some fine examples of such caps can be found at:
http://www.steadmancustomsheetmetal.com/caps.html (metal tops)
http://www.rumford.com/chimneys/chimney.html#tops (masonry tops)

Electric Draft Increasing Caps

Another category of caps contains units which function as a cap AND as an electric draft inducer. If you have draft problems that are not able to be solved by other methods, this may be the ticket. These caps have electric fans built into them which are variable speed, thereby allowing you to effectively "dial a draft" on problem chimneys. Expect to spend $900 to $1500+ installed for one of these caps.
http://www.fieldcontrols.com/chimney.top.co.html
http://www.exhausto.com/US_Home/prod01.htm

Extendaflue (flue entensions)
A new product category has recently been invented, which consists of flue extensions with integral caps. These devices solve numerous chimney problems by adding to the height, providing caps and spark arrestors and other features. Although these will not provide the same amount of boost that an electric cap can, the added height of 2-4 feet can make a difference in your chimney performance.
http://www.extendaflue.com

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