The duct fans in this category feature circular duct connections and are available as non insulated and insulated versions. They have impellers with backward or forward curved blades.

• Airflows up to 18,000 m³/h (5.0 m³/s).
• This category comprises the following product groups: CK, LPKB, LPKB Silent, RKC, BFC, IRB, IRE and IFK.