Methods and apparatus for an exhaust demand control system for measuring one or more contaminants at one or more exhaust locations within one or a plurality of exhaust ducts or plenums served by an exhaust fan system. Example systems and methods can include sensing the one or more contaminants within the one or more exhaust duct locations using a multipoint air sampling system having one or more sensors and flow control elements, comparing contaminant concentration measurements from the one or more of said exhaust duct or plenum locations against an action level to create a fan setback signal, and ensuring sensor accuracy and reliability by implementing a sensor protective mode when the contaminant concentration measurements from the one or more exhaust locations exceeds an action level.