Semi-circular ducting (or flat duct) is used where installation height is limited, allowing ventilation ducts to be concealed within shallow ceiling or floor cavities while maintaining efficient airflow where standard circular ducts cannot fit.
Ubbink Air Excellent AE35SC is the smallest semi-circular semi-rigid duct in our Air Excellent range, with a 50 x 100 mm outer diameter, designed for high-performance centralised HRV and ERV systems.
For optimal system design, recommended practice is to keep air velocity below 3 m/s to minimise airflow noise. The AE35SC is sized specifically to meet this requirement, delivering up to 33 m³/h at 3 m/s.
Compared with larger 50 x 140 mm ducts, the 50 x 100 mm AE35SC is easier to route and conceal within ceiling cavities, walls, and floors, making it well suited to space-constrained installations. However, the smaller diameter results in higher air resistance, so in applications requiring higher airflow rates or longer duct runs, two 50 x 100 mm ducts may be required where a single 50 x 140 mm duct would otherwise suffice. This approach maintains low air velocities and noise levels while offering greater flexibility in duct layout and installation.
The result is a cleaner installation, reduced pressure loss, and improved acoustic performance in well-designed ventilation systems.
