The main structure of the air duct electric heater is a frame type wall panel structure with an over-temperature protection device. If the heating temperature is higher than >120 °C, a heat insulation zone or a heat dissipation zone must be provided between the junction box and the heater, and electric heating is required. The surface of the component should be provided with a finned heat dissipation structure. The low and medium temperature air duct electric heaters do not need to be provided with a heat insulation zone or a radiator zone, and the surface of the electric heater component is naturally dissipated. The electrical control and the fan must be linked, and then the fan is started and the electric heating is started. The first time the electric heater is turned off, the time difference must be greater than 2 minutes. Control aspect. A linkage device is arranged between the fan and the heater to ensure that the heater is started after the fan is operated. After the heater stops working, the fan must be delayed for more than 2 minutes to prevent the heater from overheating and being damaged.