FIG. 1 is a perspective view of a first embodiment of a heating device showing our new design;
FIG. 2 is a front elevational view showing the design for the heating device of FIG. 1;
FIG. 3 is a rear elevational view showing the design for the heating device of FIGS. 1, 8, 10, 12, 14, and 16;
FIG. 4 is a left side elevational view showing the design for the heating device of FIGS. 1, 8, 10, 12, 14, and 16;
FIG. 5 is a right side elevational view showing the design for the heating device of FIGS. 1, 8, 10, 12, 14, and 16;
FIG. 6 is a top plan view showing the design for the heating device of FIGS. 1, 8, 10, 12, 14, and 16; and
FIG. 7 is a bottom plan view showing the design for the heating device of FIGS. 1, 8, 10, 12, 14, and 16;
FIG. 8 is a perspective view of a second embodiment of a heating device showing our new design; and
FIG. 9 is a front elevational view showing the design for the heating device of FIG. 8;
FIG. 10 is a perspective view of a third embodiment of a heating device showing our new design; and
FIG. 11 is a front elevational view showing the design for the heating device of FIG. 10;
FIG. 12 is a perspective view of a fourth embodiment of a heating device showing our new design; and
FIG. 13 is a front elevational view showing the design for the heating device of FIG. 12;
FIG. 14 is a perspective view of a fifth embodiment of a heating device showing our new design; and
FIG. 15 is a front elevational view showing the design for the heating device of FIG. 14;
FIG. 16 is a perspective view of a sixth embodiment of a heating device showing our new design; and,
FIG. 17 is a front elevational view showing the design for the heating device of FIG. 16.
The broken lines shown in the drawings illustrate portions of the heating device that form no part of the claimed design.