Type FDE swirl diffusers as supply or extract air units are particularly suitable for comfort areas like office and sales rooms. The swirling rotational and horizontal type of discharge of supply air ensures a high level of induction and a rapid reduction of jet air velocities and temperature differentials. Swirl diffusers type FDE consist of the square face plate with continuous sealing band, fixed radially arranged air control blades and the rear frame. The supply air construction contains also a perforated plate mounted at the rear frame to optimise the air distribution. To obtain low sound power levels especially at high volume flow rates, the triangular shaped, graduated air control blades extend into the corners of the square diffuser. The plenum box is supplied with side entry air connection spigot. Volume control damper and/or lip seal are available on request