Louvre - Back draught Shutters

Louvre shutters or Back draught shutters are blown open by a ventilation fan when it starts and closes by gravity when it stops. The shutters only open in one direction,  so when the fan is switched off, the louvres prevent any back draught from the wind outside entering the building. This helps to preserve heat inside the building. Commonly used on the wall mounted panel fans with the addition of a wind hood / cowl