There are a variety of chimney cowls featuring a broad spectrum of applications and uses. Chimney cowls are also known as chimney caps and are referred to as cowls due to their overall shape being reminiscent of a monk's robe, or cowl. Cowls serve to prevent strong winds driving the smoke escaping up the flue back down into the room of the heating appliance, filling the room with toxic gasses and soot. Cowls also prevent birds and small animals from nesting in the chimney. Many cowls are multipurpose and can help to address all of these issues. Some cowls are specifically made for one particular purpose. Check the product information on the cowl before you buy to make sure it is suitable for the needs of your particular home, weather conditions common in your area, and fuel that will be used. Below you will find descriptions of different types of cowls and their uses.
In windy areas flues that prevent downdrafts are a good option as they do just what their name suggests. Most are suitable regardless of the fuel type, and many also combine other features, such as preventing the entry of rain into the flue. They also prevent birds and animals from setting up residence in the chimney.
Chimney cowls designed to prevent rain from entering the flue are not always effective at helping with downdrafts or sluggish pull on the chimney flue. Check the product description and packaging to see if the cowl is suitable for these other functions.
Wind-driven cowls can help draw the smoke and fumes up and out. Extreme wind can actually help the function of wind-driven cowls and are the ideal solution for both a poor drawing flue and being in a windy area. Some of these types of cowls spin, facilitating the function of the flue. Others are designed to rotate based on the direction of the wind, ensuring they are in the optimal position to work properly and avoid downdrafts.
Spark arresting cowls were originally designed to be used on roofs that use thatch as opposed to tile or shingles. Many of these are becoming discouraged in Europe as they have to be properly maintained (removed and cleaned twice a year). If not properly maintained, they can pose a bigger hazard than a stray spark on a thatched roof, as tar builds up around the mesh, becoming highly combustible.
Occasionally, there is simply the need to keep critters out of the chimney. There are many varieties designed exclusively for this purpose and can be attractive and decorative.