Spiral duct is a type of ductwork used in heating, ventilation, and air conditioning (HVAC) systems. It is made from a continuous strip of metal, such as galvanized steel or aluminum, that is formed into a spiral shape with a series of interlocking seams. Spiral duct is flexible and can be easily bent or shaped to fit the contours of a building, making it a popular choice for HVAC systems in commercial and industrial buildings.

One of the main advantages of spiral duct is its ability to convey air efficiently over long distances. The spiral shape of the duct allows air to flow smoothly through the duct without experiencing much resistance, which can reduce the size of the duct needed to convey a given volume of air. This can save space in the building and make the HVAC system more energy efficient.