Chimney cowls are used to expel hot gases or smoke from kitchen stoves, fireplaces or furnaces. Usually with a hood-shaped cover, chimney cowls are commonly made out of galvanized iron. Other materials are also used in making cowls but galvanized iron is the most practical choice. Centuries ago, chimneys were made out of brick but as mankind progressed, it was changed to wood and then to pieces of metal. A >chimney cowl is not only used to get rid of smoke inside a room, it can also prevent backflows.

Named after monks' cowls because of its shape, chimney cowls have been used for centuries to keep wind from blowing back smoke and soot into the home. In the 17th century, this was a necessity because coal was still used. This means there were a lot of ashes coming from the chimney if there was a backflow. As the years pass, the chimney cowl has evolved into a chimney cover that prevents small animals from entering or nesting on the chimney hole to a decorative part of a house.

There are different styles of cowls for chimneys. One example is the H-style cap. This design looks like a letter H and has been used for centuries to normalize draft when there is turbulence that may cause back puffing. Although the said design is highly advantageous for homes and homeowners, it did not become as popular as the cowls we know today. Due to its bulkiness and rather weird structure, not many people liked the idea of installing it in their homes. Now that energy efficiency in homes is gaining its popularity, the H-shaped cowl is back in business since it is famous for its energy efficiency.

Other designs are founded upon the Venturi effect where updraft is increased to prevent back puffing. This results to higher consumption in energy though making them less appealing to today's homeowners.

Chimneys are still found in many buildings and homes. In the US, chimneys are called stacks in colloquial terms. Chimneys on ships however are referred to as funnels.

Chimneys pack a lot of history and this includes their cowls. Romans utilized chimney-like structures to draw out gases inside a building but the chimneys we know today only appeared in the 12th century in the northern part of Europe. By the 18th century, as the world started developing, industrial chimneys were introduced. The earliest chimney that can still be seen today is in Yorkshire. The said chimney was constructed in 1185 AD.