For homeowners trying to control water use, the Aprilaire Model 400 (AM 400) Whole-House Humidifier provides you the ability to maximize humidity control with minimal water use. In 2009, Aprilaire consolidated the Models 400M and 400A to the Model 400. The AM 400 can be mounted on the return or supply duct and like higher Aprilaire model humidifiers, the AM 400 comes equipped with digital control and can even be installed in manual mode if more control is preferred. It also features a built-in bypass damper. This drain-less humidifier utilizes new evaporative technology where gravity is used to pull water down while the wicking action of the water panel draws it back to the top, using 100% of the water delivered to the unit. This helps eliminate standing water, making the AM 400 a wise choice for homes with septic systems or locations where a floor drain is unavailable. This new evaporative technology gives the AM 400 an evaporative capacity of .70 gallons per hour, or about seventeen gallons per day.

The AM 400 is a recirculating bypass humidifier and is efficient for humidifying homes up to 4,000 square feet in size. The AM 400 can be mounted on the return or supply duct and the air flow can run in either direction. Although the AM 400 uses a different drain less technology with the help of the built-in bypass damper, it replaces the Models 225, 445, 445-A and 448. In addition to the digital humidistat and bypass damper, the AM 500 features an outdoor temperature sensor, two humidifier water panels, a saddle valve and a 24 Volt transformer. Similar to the AM 500, the 400 instead comes equipped with two water panels instead of one. Different than other conventional water panels, the 400 series water panel is an absorbent paper mesh that can wick up the water from the reservoir. The outside temperature sensor is separately installed and works with the humidistat to automatically dial back the humidity when the temperature drops.

The automatic digital control panel, or humidistat, that is present in many of the new Aprilaire model humidifiers has a number of components that present numerous advantages. The panel digitally displays the relative humidity level and shows that the unit is operating so that you know what the unit is doing and how much humidity is present in your home. In addition, it gives service alerts and notifications when it is time to replace the water panel. Like higher Aprilaire model humidifiers, the AM 400 connects to the furnace thermostat terminals allowing the humidistat to sense when the furnace is providing hot air and adjust accordingly. The AM 400 comes with a five year warranty like other Aprilaire humidifier units and it is recommended to have the water panels replaced about every year. Homeowners have the option of purchasing the new Aprilaire 400 Humidifier Annual Maintenance Kit to help guide you through the proper maintenance practices for this unit. This kit also provides AM 400 parts and tips on how to maximize your humidifier unit to keep it running at the optimum level that it has proven to perform at.