The Aprilaire 4640 is the correct replacement for the following humidifiers:

• Aprilaire 500
• Aprilaire 500A
• Aprilaire 500M

The Aprilaire 4640 Humidifier Scale Control Insert is for use in your 500 series model humidifier. This Aprilaire humidifier scale control is a U-shaped piece that encases your humidifiers water panel evaporator.

The Aprilaire 4640 Specifications:

• Contains 1 humidifier scale control insert
• Works with your 500 series model humidifier
• Item Weight: 4.8 ounces

The Aprilaire humidifier scale control will direct mineral build up back into your humidifiers evaporative pad, keeping it out of your clean, humidified air. This humidifier scale control is a key feature to keeping your Aprilaire 500 series model humidifier working at its best.