Please read the description Greenwood CV3 Extractor Fan 100mm White Mains (Very Silent). Condition is New. Dispatched with Evri Tracked. Your fan has already been commissioned for you. When first 'powered up' your fan will automatically set up its required airflow rates for trickle and boost. Trickle: A quiet, continuously running extract ventilation at a low speed Boost: A higher speed, activated via a 2 minute delay-on-timer, when turning on the bathroom light Your fan has been designed to ventilate the room continuously (i.e. 24/7) to improve the indoor air quality and enhance your comfort.