Metal chimneys are used for a variety of reasons, including wood stoves, pre-fab fireplace installations and gas venting. With metal chimneys, a chimney cap needs to be placed on the top. Since there is nowhere for the rain to go with these types of applications, a chimney cap sends rain water away from the chimney. This protects the stove, fireplace or heater from rain water, which will in turn damage the walls and ceilings.
Another reason why chimney caps are necessary is because mammals, including birds and squirrels, are capable of nesting in the chimney. A chimney cap prevents the nests from forming and clogging up the space.
Finally, because metal chimneys are made with layers of metal with no insulation, water and moisture can get in between these layers and cause early damage. With a cap, this problem is avoided and allows water and moisture to escape.
Not all chimney caps are the same. If you have draft problems, you’ll want to choose “draft increasing” caps that cause winds to create upward drafts through the chimney cap. If you don’t have draft problems, any replacement cap is suitable. Try to find a cap that matches the brand of your chimney, as this ensures that both pieces will work together efficiently.
If you cannot find a cap in the same brand, a generic brand is also acceptable. Just be sure that you speak with the store or manufacturer to ensure that the cap can be used with your chimney. Also consider the material of the chimney cap, as standard caps can be made from steel, stainless steel, aluminum and copper.
Copper is often the material of choice, as it’s decorative, elegant and ages well. Instead of rusting, the patina turns a greyish color and prevents the metal from erosion. Low maintenance and a low cost also make copper chimney caps an excellent choice. With the wide variety of copper selections available through manufacturers, there are many options for homeowners that will turn their home into something spectacular.
Reference: Heart.com Articles