A heating element includes a flexible substrate, a layer of adhesive disposed on a surface of the substrate, and a continuous strand of electrically conductive wire disposed on the adhesive in a pattern of coil structures. Each coil structure includes a first coiled part and a second coiled part. The wire in the first coiled part forms a counterclockwise pattern from an outermost turn to an innermost turn of the first coiled part, and the second coiled part has an innermost turn beginning at an end of the innermost turn of the first coiled part. The wire in the second coiled part forms a clockwise pattern from the innermost turn of the second coiled part to an outermost turn. A connector segment of wire connects outermost turns of adjacent ones of the coil structures.