The EXP Expander Box Weather Louvre unit is used with AFP’s DUX range of pressure relief vents in halocarbon installations. It has been specifically designed to provide a Free Vent Area (FVA) matching that of DUX while providing the weather protection essential for two-way vents in exterior walls.

The weather sealing must be maintained while supporting two-directional flow, a sealed external unit cannot be used, making an open louvre design essential.

The louvre blades are assembled into a custom-designed ‘Expander Box’ – hence EXP – which increases the effective FVA to match the 85% FVA of the DUX. The result is a fixed blade louvre larger than the internal vent, offering no restriction and adding zero to the Vent Dynamic Coefficient (vDc). (Other fixed louvres on the market typically provide at most only 50% FVA)

The EXP 300 & 500 are fitted with a new storm shield which is a carefully designed mesh that prevents storm blown rain entering behind the unit whilst having zero effect on any blast protection.


  • NEXT DAY DELIVERY on 300 & 500 units if order is processed before 12pm
  • The EXP comes in powder coated steel construction RAL9006 Grey as standard, special colours available upon request
  • Manufactured to ISO9001
  • The products carry a 5-year guarantee
  • The EXP is surface mounted unit
  • Can be retrofitted
  • The EXP comes with fitting kit