Roof systems are elements of the ventilation system mounted directly on the roof, chimney or ventilation duct. They are available in a variety of forms and are used to extract unwanted gases, prevent the entry of rain into a chimney or prevent downdraughts. Sometimes a roof fan is the most efficient way to rid a building or facility of overheated air issues. Since hot air rises to the ceiling or the highest point of a structure, it makes sense that having exhaust fans mounted on the roof will work best. Not all facilities can utilize a roof exhauster due to weight issues, pitch of roof, access to the roof and so on.