The Aprilaire 600 Humidifier is thebest bypasshumidifier on the market today. Capable of evaporating up to 4,000 square feet, this 24V whole house humidifier with automatic digital control uses a Water Panel evaporator to deliver 3 gallons an hour Easy to use, this Aprilaire whole house humidifier offers the best regulation for home humidity levels while sporting one of the highest evaporation rates in the industry at .70 gallons per hour In addition, it operates quietly and maintenance is a cinch The Aprilaire 600 humidifierfeatures a builtin damper which means you can avoid the need for an addional part and it gives you additional control. A small damper handles allows you to adjust the damper. This Apirlaire bypass humidifier features a water panel indicator light so you'll know exactly when to change the humidifier filter. The Water Panel evaporator shoud be changed at least once per year. Get the peace of mind with an increased comfort with consistent humidity levels in your home. NOTE: Aprilaire 600 humidifierMust be PROFESSIONALLY INSTALLED by a licensed HVAC professional to be eligible for the Aprilaire 5year warranty. Warranty is void unless humidifier is installed by qualified heating amp; air conditioning contractor due to possible misapplication of product.