A positive-temperature-coefficient heating element (PTC heating element), or self-regulating heater, is an electrical resistance heater whose resistance increases significantly with temperature. The name self-regulating heater comes from the tendency of such heating elements to maintain a constant temperature when supplied by a given voltage.

PTC heating elements are a type of thermistor.

PTC heating elements have large positive temperature coefficients of resistance, which means if a constant voltage is applied, the element produces a large amount of heat when its temperature is low, and a smaller amount of heat when its temperature is high. In comparison, most electrical heating elements also have positive temperature coefficients, but those coefficients are so small that the elements produce approximately the same amount of heat regardless of temperature.

Some PTC heating elements are designed to have a sharp change in resistance at a particular temperature. These elements are called self-regulating because they tend to maintain that temperature even if the applied voltage or heat load changes. Below that temperature, the element produces a large amount of heating power, which tends to raise the temperature of the heating element. Above that temperature, the element produces little heating power, which tends to allow it to cool.

In some applications, this self-regulating characteristic allows PTC heaters to be used without thermostats or overtemperature protection circuits. One very important use of self-regulating heating elements is to assure the heating element will not become so hot as to damage itself or other parts of the heater. In some applications where the heating element is directly connected to the item being heated a self-regulating heater may also provide adequate temperature control of the item to be heated.

However, many applications require control of two temperatures. For example, space heaters use heating elements much hotter than the room being heated. In these applications, a thermostat may be better able to sense and control the temperature of the item being heated. Nevertheless, a self-regulating heating element may still be used to keep the heating element from damaging itself or other parts of the heater.

If the heat required to hold the desired temperature is known, a PTC heating element can be selected to provide the correct amount of heat at the desired temperature. Such a heating element will warm up quickly because it produces more heat at low temperatures. In contrast, a conventional heating element that produces the correct amount of heat at the desired temperature will produce the same amount of heat at low temperature, resulting in long warm-up times.

In some applications it is desirable to regulate the heat output (typically measured in watts) as opposed to regulating the temperature. The heat output of any electrical heating element can be regulated by regulating the electrical power input. PTC heating elements also can be regulated indirectly. For example, a PTC heating element with a sharp change in resistance at a particular temperature can be fitted with a constant voltage source and a variable-speed fan. With the fan at a low setting, the heating element draws only a small amount of current, resulting in a low heat output. With the fan at a high setting, the air draws away more heat, and the heating element responds by producing more heat.^{[citation needed]}