Aluminium gravity grilles — passive backdraught prevention on exterior walls and exhaust openings

Gravity grilles operate on the simple principle of their own blade weight: when the fan operates and exhaust air pressure exceeds external pressure, blades are pushed open allowing air discharge. When the fan stops, blades fall back to closed position under gravity, preventing backflow of cold or warm exterior air. Advantage over spring-loaded backdraught shutters: gravity grilles have no spring to wear or jam. Reliable operation for decades with zero maintenance. Opening pressure is determined solely by blade weight — lower than spring shutters, so installation pressure drop is minimal. Applications: bathroom, kitchen, basement and plant room exhaust — wherever an intermittent exhaust fan must prevent cold air circulation during off periods.