controller 32 commands fan motor 19 to run at a third speed slower than the second speed this third speed corresponds to a ventilation air flow mode which may be 130 cubic feet per minute cfm in exemplary installations the third speed of fan motor 19 will vary depending upon the ventilation demand of the space supplied by supply air duct 24 for example the third speed of the fan motor 19 may be set based on regulations from industry entities e g ashrea 90 1 to meet certain minimum ventilation levels or ventilation demands of the space supplied by supply air duct 24 the installer may program the third speed of fan motor 19 as a fraction of the first speed or second speed further the third speed of fan motor 19 may be programmed into controller 32 by an installer when the system is installed this allows the ventilation demands of the space to be determined before the third speed is set at 114 controller 32 adjusts positions of the inlet air damper 30 and a return air damper 35 in ventilation mode controller 32 opens inlet air damper 30 and closes return air damper 30 such that so that the airflow that is being circulated through the space is close to being 100 outdoor air return air from return duct 31 is drawn through exhaust air vent 27 and by exhaust fan 28 at 116 controller 32 monitors temperature of the space e g via thermostat 40 to determine if the space has become too warm or cold in response to the influx of outdoor air in exemplary embodiments fan motor 19 is a three speed motor that operates at the first speed.