Abstract: A dual fitting chimney cap adapted to be connected to chimney stacks of differing sizes, the chimney cap including a cylindrical housing having an upper housing portion formed with a plurality of apertures, and a lower housing portion for attachment to an upper open end of a chimney stack of conforming cylindrical contour, the lower housing portion having a cylindrical cross-section of a presecribed diameter, and an annular transition portion integrally interposed between and interconnecting the upper and lower housing portions, the annular transition portion including a first annular region and a second annular region integral with and interconnected to the first annular region, the first annular region having a prescribed diameter larger in dimension than the diameter of the second annular region and also larger in dimension than the diameter of the lower housing portion, the second annular region having a prescribed diameter smaller in dimension than the diameter of the lower housing portion.