Constant Air Volume fume hoods, also know as by-pass air fume hoods, are designed to operate in a building where the HVAC supply air and exhaust air volumes do not vary.

These fume hoods maintain a relatively constant air volume regardless of the sash position. They do this by incorporating an automatic by-pass which limits the increase in face velocity as the vertical rising sash is lowered below 18” open. Room air is drawn between the top of the sash and the roof of the fume hood diverting the incoming air away from the open sash.