Aprilaire 4640 Scale Control Insert 323613-751 20" WC Calibration: Ensures the

20" WC Calibration: Ensures the system only ignites when the correct negative pressure is achieved

Always verify the status chart on the blower door after installation

This model features dual SPDT switch outputs that operate in sequence

streamlining installation in tight plenum spaces

Aprilaire 4640 Scale Control Insert 323613-751 20" WC Calibration: Ensures theMaintaining your whole home humidification system requires precision engineered components like the Aprilaire 4640 Scale Control Insert. This genuine Aprilaire replacement part is specifically designed to encase the humidifier water panel, serving as a structural U shaped insert that guides water flow and manages mineral accumulation. Constructed from durable, heat resistant polypropylene, the 4640 insert effectively captures heavy scale buildup and