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. It not only recycles water cleanly into the air, but can help eliminate water where draining is not available. The Aprilaire 400 humidifier does not require much maintenance at all. You should visually inspect the unit every 500 hours, more frequently during heavy use. Inspect the Plumbing and water lines for cracks or leaks and replace as needed. The one item that does require to be replaced is the water panel. The water panel should be replaced annually during regular use and every six months during heavy use. Are you tired of dry skin, splitting or cracking on your hard wood floors or trouble breathing in your home these can all be signs of a lack of moisture within your airflow, meaning that you and your family will benefit greatly from the Aprilaire 400. Note: heat pumps: Aprilaire 400 model can be installed in heat pump applications. However, due to the fact that heat pumps deliver lower temperature air to the home than gas furnaces, evaporation will be approximately 60 of rated capacity. (With other Aprilaire models hot water can be used instead of cold to maximize evaporation. However, due to the nature of the wicking water panel in the 400 model hot water provides no extra benefit.