The RW Simon Vent-A-Matic circular window vent is a non-electric window ventilator designed for kitchens, bathrooms, and bedrooms. It is sized to fit holes measuring 162mm (6.5 inch) in sealed double-glazed windows measuring 12-32mm thick. The vent is equipped with a diffusing rotor to prevent draught and improve fresh air distribution, helping to prevent condensation in most sized rooms. It includes an integrated storm guard to help reduce drafts. The rotor is designed to operate on its own inertia even when air pressure is equalized.