A dryer exhaust duct power ventilator which is free of any dedicated internal air flow contacting devices for sensing air pressure or measuring fan RPMs and free of any hall effect sensor, but instead utilizes the auxiliary winding of a PSC motor on a centrifugal duct fan to measure the rotation of the motor and fan and thereby determine the pressure in the duct. A clip-on current sensor is located in the dryer power connection compartment and is used to detect operation of the dryer.