The ÆP and pseudo-ÆP systems, due to their simplicity will typically cost less than a ÆV system for the same laboratory. How much less depends upon the size and complexity of the laboratory ventilation system and the type of fume hood controls. As the number of measured and controlled devices increases so will the differential cost. If exhaust and supply volumes are measured at only one position each, the cost differential will decrease. However, if you have chosen VAV fume hood controls and general exhaust controls that have flow measurement capability built into each, then only a supply air flow measuring device and controller are needed to complete the system. In this case the cost of the two systems may be negligible. It is difficult to divorce the cost of the space pressure controls from the cost of the fume hood controls since they are often integrated.