Auditorium Step Swirl Diffuser

Smartemp CSS-FD

Step swirl diffuser for high induction discharge from steps in tiered auditoria and lecture theatres.

The SMARTEMP Auditorium Step Swirl Diffuser, type CSS-FD, discharges supply air in a fixed radial discharge pattern. The diffuser is mounted in the vertical face of auditorium steps. Highly inductive swirl discharge directed away from the sensitive ankle regions of seated occupants strongly dilutes the supply air stream with room air and rapidly breaks down the discharge velocity. This ensures draught-free air supply for displacement airflow in tiered auditoria, providing occupants with enhanced levels of thermal comfort and increased indoor air quality.

The CSS-FD diffuser is well suited to steeply raked auditoria, such as sports arenas. The radial discharge supply air pattern attaches to each vertical step face, stabalising the lake of cool displacement air at ankle height above the floor tiers. This prevents the cool displacement air from cascading down the steps, thereby preventing draughts at ankle height, and ensuring that the displacement cooling effect is also retained at higher tier levels rather than accumulating in a waterfall effect that overcools the front tiers


Displacement airflow
Thermal displacement airflow, with low level swirl supply from steps beneath seats. Heat and contaminants rise from occupants in convective plumes to stratify at a high level. Enhanced levels of thermal comfort and indoor air quality are attained in the occupancy micro-climate.

Wall location
Air supply from vertical step face.

VAV dependent throw
Suitable for VAV applications. Horizontal coverage dependent upon airflow rate.

Fixed direction
Highly inductive swirl pattern parallel to vertical step face.

Circular face shape
Round face flange. Radial face pattern: Visible swirl vanes.

Plastic face
Visible parts made of V0 fire retardent ABS, dyed grey or black. Bespoke colours available depending on quantity.

Airflow rate

  • ≤ 16 L/s (58 m³/h)

Nominal neck sizes

  • DN100
  • DN125

Sound power level

  • ≤ 18 dB(A)


  • For tiered auditoria and lecture theatres
  • Location independent of seating
  • Built into step front at apptroimately 100 mm height
  • High induction swirl discharge breaks down discharge velocity and equalises temperature.
  • Installation in wooden or concrete steps
  • Connection to pressurised plenum


The SMARTEMP Auditorium Step Swirl Diffuser, type CSS-FD, produces high induction swirl discharge from the vertical step face beneath tiered auditorium seating. Intense mixing of room air into the supply air stream directly at the diffuser face breaks down the discharge velocity and raises the supply air stream temperature by dilution to ensure draught-free airflow in the ankle regions of seated occupants, producing a zone of cool, high quality air at the base of the tiered seats. The discharge pattern is parallel to the vertical step face, creating a vertical barrier to stabalise the pools of cool ankle level air from cascading down the tiered steps. This is especially beneficial in steeply raked applications, such as lecture theatres and sports arenas.

Velocities in the ankle regions of seated occupants are low, preventing the sensation of draughts. A low level occupancy microclimate of enhanced indoor air quality is created, in which thermal plumes from occupants and other heat sources rise upwards by convection. This draws in high quality air from the occupancy microclimate, enveloping occupants in cooler, high quality replenishment air. Heat and contaminants stratify at a high level in concentrated form, to be removed from the space.

Due to stratification of heat, relatively large supply-to-return temperature differentials are achievable – dependent on ceiling height – despite the relatively high supply air temperature (typically 18°C), thereby minimising fan energy requirements. Energy savings also accrue from the extended free cooling range often achieved by the elevated supply air temperature, as well as from the potential to reduce outdoor airflow rates due to the improved ventilation effectiveness of the low level displacement supply.

Product Type




Face Material

Face Pattern

Face Shape

Airflow Direction

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