What distinguishes a chimney cap from a rain cap?

A chimney cap is designed primarily to protect the structure of the chimney by preventing water from entering and causing damage to the masonry and flue. It's a broader term that includes various protective features, such as preventing downdrafts and assisting with ventilation. In contrast, a rain cap is a specific attachment that fits over the flue to prevent rain from entering while also serving to shield the internal flue components from moisture and debris.

The distinction between the two lies in their purposes: the chimney cap serves a more general protective role for the entire chimney and its structure, while the rain cap focuses specifically on the flue's interior protection against rain and other elements. Thus, option B accurately reflects this specific role of each component.