HVAC Ductwork - Square vs Round

Have you ever wondered why some have a square shaped ductwork for their central air conditioning system, while others have circular shaped? Some may guess that it's the preference of the HVAC contractor or maybe there's a technical reason?


Central air conditioning ductwork is chosen based on size, shape, and material. Square or rectangular ductwork is often preferred because it fits easily into tight ceiling and wall cavities. Square ductwork will carry more cfm at the same velocity compared to the round version of the same vertical dimension. This means it will fit in smaller spaces without reducing flow. Also square ductwork is easier to fabricate on-site. It's often more cost effective to transport flat sheets to the building site and it's fairly easy to put them together.

However a lot of ductwork is round. Round ducts are considered to be the most efficient, allowing a greater volume of air movement per unit of duct.

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