Underfloor air distribution (UFAD) is an air distribution strategy for providing ventilation and space conditioning in buildings as part of the design of a HVAC system. UFAD systems use an underfloor supply plenum located between the structural concrete slab and a raised floor system to supply conditioned air to supply outlets (usually floor diffusers), located at or near floor level within the occupied space. Air returns from the room at ceiling level or the maximum allowable height above the occupied zone.