The Helios Silent Box (SB) range of Quiet in-line Centrifugal fans, offer a very quiet way to ventilate noise sensitive areas, using ducting up to 400 mm diameter. These Quiet in-line Centrifugal fans combine the high-pressure benefits of a centrifugal fan with the reduced sound levels using sound reducing insulation to provide quiet air movement. Because they are powerful these fans ensure that the system will move air even when the system resistance is much higher than expected. Thus the Silent box range is able to quietly cope with moderate runs of flexible duct as well as spiral ducting. Installation is easy with simple mounting feet included with the fan. Can be mounted in any position including bottom access for false ceilings.