In-line centrifugal fan. Low high casing rectangular in section manufactured from galvanised steel with rigid circular spigots fitted to both ends of the case. Fan assembly incorporates a high efficiency; backward curved impeller and a IP44 rated motor with integral 'Heatseeker' thermal overload protection. Fan assembly can be removed to reverse air flow direction. Unit supplied with unique, one bolt mounting bracket for ease of installation. The unit includes integral control of fully variable fan speed. The control optimises the parameters in response to the output of the matched range of S.E.L.V. sensors.