CAPS
Having a chimney cap is one of the best things that you can do for the long term life of your chimney. Chimney caps keep rain water, sticks, leaves, and debris out of the chimney. Squirrels, raccoons, and birds can become trapped in your chimney or build a nest blocking the chimney's exhaust. Over time, rain and water can do thousands of dollars damage to the masonry work.
Additionally, chimney caps act as spark arrestor: the same lid that prevents rain from falling into the flue also acts to catch any burning embers or sparks that are caught in the draft of the fireplace. This floating, flaming debris can damage nearby structures like the roof, leading to house fires in the worst cases. This risk is greatly increased in the event of a chimney fire, as the flaming creosote and extremely high flue temperatures represent a significant threat to the home. While the best protection against chimney fires is regular sweeping and inspection, chimney caps can help to contain and minimize the damage done by chimney fires.