Have you taken a look up at that big, brick chimney since you purchased your home? When going through the home buying process, it is a necessity in some buyers eyes. The main focus tends to lean towards the fire safety aspects but homeowners will find just as much harm can be found allowing mother nature a pathway into their home.
A Chimney Cap is a prefabricated lid attached to the top of the flue system. There are many types of caps and some have more functions than others. Standard chimney caps for masonry chimney's can be found to fit your specific flue tile size and screw tightly to the flue preventing separation during windy conditions. The screen prevents animals and debris from blowing into the flue system. Depending on the type of metal used the longevity of a cap can be quite long. Rusting will eventually create pinholes in the metal, destroying its integrity. A Lock Top Damper, is a cap with an extra function. It also replaces the firebox's damper. The spring loaded mechanism is attached to a stainless steel wire which gives the ability to open and close the flue system from the top of the flue. This can be operated from the comfort of your own home in the firebox. This prevents virtually anything from entering the flue while it is closed. Some chimneys do not have a flue with standard flue tile or have multiple flues using one chimney. With these chimneys, the cap must be made to custom fit the top of the entire chimney.
Nowadays, most homes with a fireplace have prefabricated units installed. These units are installed in wooden frames with a metal top covering the space between the outside of the frame and the flue. This is called a chase cover and the pipe/flue will extend through it and will have a storm collar to further prevent any windblown rain into the frame. These systems have very specific caps to the make and model. As with the masonry chimney caps, the chase cover, cap and storm collars must replaced over time due to rust. There are rust proof options out there but they will increase the cost significantly.