Certain embodiments provide a heater. The heater includes an inner electrical conductor. A heater section at least partially surrounds the inner electrical conductor. The heater section is configured to generate an electrically resistive heat output during application of time-varying electrical current to the heater section. The heater section includes ferromagnetic material. An outer electrical conductor at least partially surrounds the heater section. An applied time-varying electrical current is configured to propagate through the inner electrical conductor and the outer electrical conductor in substantially the same direction. The applied time-varying electrical current is configured to propagate through the heater section in a substantially opposite direction. The heater provides a first heat output when time-varying electrical current is applied to the heater below a selected temperature, and a second heat output approximately at and above the selected temperature during use. The second heat output is reduced compared to the first heat output.