Square duct lines are a type of ventilation system used to distribute air throughout a building or structure. They consist of a series of square or rectangular metal ducts that are connected together to form a network of air channels. The ducts are typically made of sheet metal and are joined together using fasteners, seals, or adhesives. Square duct lines are often used in commercial and industrial buildings, as they offer a number of benefits over round ducts. They are more efficient at moving air, as they have a larger cross-sectional area and are less prone to air leakage. They also take up less space and are easier to install than round ducts, making them a cost-effective choice for many applications. Square duct lines are an essential component in any ventilation system, as they help to ensure a healthy and comfortable indoor environment.