Horizontal discharge roof fan with efficiency-optimized aluminum housing and a newly developed high-performance centrifugal impeller. The housing is made of seawater-resistant aluminum with integrated intrusion protection. The motor support plate and base plate with inlet nozzle are made of galvanized steel. The base plate features threaded screws for attaching suction-side accessories. A protective grille is standard on the outlet side in accordance with safety standards. The high-performance centrifugal impeller has backward curved blades made of plastic and is dynamically balanced in accordance with industry standards. It includes a speed-controllable three-phase external rotor motor in an enclosed design with moisture protection. The ball bearings have moisture protection insulation and are maintenance-free and interference-free. An external inspection switch is standard, with a protection class of IP 65.