How Do Heated Seats Work?

Heated seats are often thought of as a luxury item and are most often included in high-end cars. The actual technology behind heated seats, however, is no different than that used in electric blankets, hair dryers, water heaters and anything else that uses electricity to produce heat. Heated seats are powered by a heating element, a long strip of material that functions as a resistor. A resistor resists the flow of electricity. When electric current flows through it, the energy is turned into heat, which flows through the seat, warming the rider.

As with the lights in your car, the heated seats are controlled by a type of switch called a relay. A relay allows a small electric current to control a much larger one. When you flip the switch to turn on the seat heater, a small current flows through a coil in the relay. Near this coil is an open switch. When current flows through the coil, it creates a magnetic field, which pulls the switch closed. This completes a circuit, sending electricity from the battery to the seat cushion heating element. The audible click you can hear in some cars when you turn on the seat heater is the relay closing.

The longer the seat cushion stays on, the hotter it gets. If it were to stay on for too long, it would get hot enough to become uncomfortable or even dangerous to sit in. It could even start a fire in the cushion. To prevent this, most car seat heaters have a thermostat. The thermostat measures the temperature in the cushion. When it reaches a certain temperature, the thermostat sends a signal, automatically turning off the relay until the seat cools down a bit. At that point, the thermostat turns the relay back on again. Many seat cushions also have "high" and "low" settings that let the driver control the temperature of the seat cushions.