The Fan Return or Exhaust Volume Match Control module controls a variable speed fan and maintains a volume differential between the supply and return or exhaust ducts in an air handler application. This module accepts return or exhaust and supply flows, a low limit temperature, and setpoints. The module has outputs for controlling a variable speed return or exhaust fan. In addition to the volume matching capabilities, this module also has a low limit function where the differential flow setpoint is decreased when the low limit temperature is below the low limit setpoint.