Abstract: A chimney cap assembly for use in the installation of non-masonry chimneys including a chimney chase and a centrally extending chimney pipe. The chimney cap assembly includes a one-piece chimney cap for positioning upon the chimney chase. The chimney cap includes a central opening shaped and dimensioned for positioning about the chimney pipe, wherein the central opening includes an upwardly extending flange. The chimney cap assembly further includes a collar member having an inner edge positioned at the top of the collar member and an outer edge positioned at the bottom of the collar member. The collar member is positioned above the chimney cap such that the bottom of the collar member substantially overlaps the upwardly extending flange along a longitudinal axis extending along the chimney pipe. In addition, the inner edge of the collar member is secured to the chimney pipe creating a seal therebetween.