FIG. 1 is a perspective view of an ornamental design for a heater.
FIG. 2 is a front elevation view of the heater of FIG. 1.
FIG. 3 is a rear elevation view of the heater of FIG. 1.
FIG. 4 is a left side elevation view of the heater of FIG. 1.
FIG. 5 is a right side elevation view of the heater of FIG. 1.
FIG. 6 is a top plan view of the heater of FIG. 1; and,
FIG. 7 is a bottom plan view of the heater of FIG. 1.
The broken line illustration of feet, symbols included on the display or buttons, screw inserts, seams, top and bottom parts connecting the louvers to the air outlet frame, recessed horizontal bar behind the louvers, recessed inlet vent structure, and flanges is shown for the purpose of illustrating optional structure of the article and forms no part of the claimed design.