Furnace

FIG. 1 is a front, left and top perspective view of a furnace showing my new design;

FIG. 2 is a rear, right and bottom perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a right side view thereof;

FIG. 7 is a top view thereof;

FIG. 8 is a bottom view thereof; and,

FIG. 9 is a front, left and top perspective view of the furnace in a state of use.

The broken lines depict portions of the furnace that form no part of the claimed design.