Can Fan RK-S All models have a multi position 4 speed control switch. The four distinct graduations are approximately 25% 50% 75% 100% of normal RK performance. Better temperature control Better airflow Better odour control Consistent negative room pressure Better economy The fan is equipped with a thermal switch that turns off the motor if it reaches a dangerous working temperature (for instance in a case where a large amount of debris blocked the working mechanism). The Swiss made motor combined with the German engineered propeller design enables this model to deliver the strong airflow you need while 4 speeds enable adjustment as needed depending on seasonal growth requirements. The low noise levels will impress you.