A heater includes a resistance coil, a first conducting pin and a second conducting pin. The resistance coil includes a first end connected to the first conducting pin, and a second end connected to the second conducting pin. The resistance coil defines a first portion adjacent the first end, a second portion adjacent the second end, and a third portion disposed between the first portion and the second portion. At least one of the first, second, and third portions has a continuously variable pitch along its length.