Espada duct fans are typically found as boost fans within long duct runs and trickle extract fans due to the nature of them moving the air in-line with the axis of the impeller. The Espada is often used as bathroom extract and in hydroponic applications where humidity is high. The lightweight yet durable plastic casing is designed to fit directly into spiral ductwork for a quick installation. Due to the lower flow rates and pressure, tube fans have very low noise levels making them ideal for installation into ceiling voids.
You may also be interested in the Ropera Duct Fan which offers a more robust metal case and an EC option.