In many ways, round metal duct work is more economical than rectangular metal duct work as a means of conveying air.
1) Size: For a given pressure loss, the surface area of rectangular duct can be double the comparable round duct surface area. Round duct, therefore, requires less metal than rectangular equivalents. Rectangular duct work often requires heavier gauges, additional reinforcement, and heavier, shorter sections.
2) Installation: The reduced area of round duct makes it easier to handle, lift and install. Because it is available in longer lengths, round duct requires fewer costly joints in the field and less sealing. And, rectangular joints are more expensive in themselves.
3) Efficiency: Using round duct achieves a better-sealed system. With lower pressure drops, less fan horsepower is required to move the air, and as a result smaller equipment can be used. All of which results in lower operating costs.
4) Design: Many architects and designers are using the aesthetically pleasing shape of the round metal ductwork as unique elements in their designs.
5) Healthier: Finally, round duct can help to create healthier indoor environments. With less surface area, no corners, and better airflow, round metal duct work eliminates the chances of dirt and bacteria accumulating in the duct.