Should the chimney cap be the same dimensions as the chimney base?

The chimney cap should indeed overhang the chimney base. This overhang serves multiple important purposes. Firstly, it prevents rain and snow from entering the chimney, which can lead to water-related damage and the deterioration of the chimney structure over time. Secondly, it helps to protect the masonry or other materials used in the chimney construction by directing water away from the chimney sides. Lastly, an overhanging cap can also help to reduce the risk of chimney fires by preventing embers from escaping into surrounding areas, as they are more likely to be contained by a larger cap.

The dimensions of the chimney cap are designed in such a way that it extends beyond the edges of the chimney base. This design consideration ensures adequate protection and drainage, which enhances the longevity and safety of the chimney system.