I claim the ornamental design for a heating element, as shown and described.
FIG. 1 is a perspective view of a heating element.
FIG. 2 is a side elevation view of the heating element shown in FIG. 1.
FIG. 3 is an opposite side elevation view of the heating element.
FIG. 4 is a front elevation view of the heating element.
FIG. 5 is a rear elevation view of the heating element.
FIG. 6 is bottom elevation view of the heating element.
FIG. 7 is a top elevation view of the heating element; and,
FIG. 8 is a side elevation view of the heating element shown in FIG. 2 from an opposite side of that shown in FIG. 2.
The broken lines shown in the figures are for the purpose of illustrating environmental structure of the heating element, and form no part of the claimed design.