The Aprilaire 400 humidifiers a 24 volt drainless whole house humidifier with automatic digital control. The Aprilaire state of the art humidifier utilizes gravity to pull water in and disperse it into the air, utilizing 100 percent of water to add moisture to your air. By evaporating up to 0.7 gallons of water per hour, yours never have to experience the discomfort of dry air again best of all, the wide ranging effects of this device can reach all rooms in a tightly constructed home of up to 4,000 square feet if you are all about water conservation or live in an area where standing water can become a problem, donrs wait another day to get the Aprilaire 400 whole house humidifier.