The ornamental design for a ceilingfandownrodsheath, as shown and described.
FIG. 1 is a bottom perspective view of a ceiling fan downrod sheath showing an embodiment in accordance with my design;
FIG. 2 is an enlarged top plan view of the ceiling fan downrod sheath in accordance with my design;
FIG. 3 is an enlarged top perspective view of the ceiling fan downrod sheath in accordance with my design;
FIG. 4 is an enlarged front elevation view of the ceiling fan downrod sheath in accordance with my design, the opposite side view being a mirror image of that shown;
FIG. 5 is an enlarged side elevation view of the ceiling fan downrod sheath in accordance with my design, the opposite side view being a mirror image of that shown; and,
FIG. 6 is an enlarged bottom plan view of the ceiling fan downrod sheath in accordance with my design.
The broken lines showing the environmental structure are for illustrative purposes and form no part of the claimed design.