About the Aprilaire 4010 humidifier transformer the Aprilaire 4010 humidifier transformer provides the ability to convert 110Volt to 24 volt for installation. The leads connect to your 110 volt supply and the screw terminals then provide the 24 volt output to the humidifier. The Aprilaire 4010 humidifier transformer is designed for use with Aprilaire humidifiers 400, 550, 550a, 558, 560, 560a, 568 amp; 600.