How many sheet metal screws or rivets are required to mechanically fasten round metallic ducts?

Under the International Mechanical Code (IMC), the requirement for fastening round metallic ducts is established to ensure structural integrity and prevent mechanical failures or leaks in the duct system. The code specifies that a minimum of three sheet metal screws or rivets should be used to securely fasten the joints of round metallic ducts.

Using three fasteners provides adequate support and helps distribute the loads across the joints, reducing the risk of failure due to pressure changes or thermal expansion that may occur within the ductwork. The number three is significant as it ensures that the connection is stable; if one connection were to fail, the duct would still be secured by the other two connections, thus maintaining its integrity during operation. This approach helps in promoting durability and reliability in HVAC systems.

The other options, while they represent lower numbers of fasteners, do not comply with the minimum requirement set forth by the IMC for effective fastening in order to maintain the performance and safety of the ductwork.