Inline Duct fans are exhaust fans mounted in-between ducting, hence the name inline duct fan. For instance, if you wanted to ventilate an area that did not have clearance or space for a ceiling mount fan, you would make use of inline exhaust fans to ventilate the area. The exhaust fan would be placed in between the ductwork and the stale air would travel through the ducts and ultimately be removed from your home. Since inline fans are not mounted directly to the ceiling, they are very quiet. When installing an inline fan, to reduce noise, an insulated flex duct at least eight feet long from the intake port on the ceiling to the inline fan is recommend.