AprilAire introduced the first evaporative humidifier for forced air furnace systems back in 1954. Since that time, AprilAire continues to lead the industry in whole home humidification systems. Our evaporative humidifiers work by piping water into the distribution tray located at the top of the humidifier. The water is uniformly distributed across the width of the tray and through a scientifically designed system of outlets. It flows by gravity over the Water Panel evaporator. Dry, hot air from the HVAC system is moved through the moisture-laden Water Panel evaporator. Natural evaporation takes place, the water is turned to vapor, and the humidified air is circulated throughout your home. This unit is uniquely designed to evaporate 100% of the water going into the humidifier. It incorporates a special two-stage float system to maintain the optimal amount of water and protect against overflow. In the unlikely event the float system fails, it is recommended an overflow tube (1/2 inch inside diameter) be installed to the base of the humidifier and run to a condensate pump, a sink, or a floor drain. Follow the required maintenance instructions. INCLUDED IN THE BOX: Installation instructions and template, humidifier with built-in bypass damper, 24 VAC transformer, manual humidifier control with sensor, saddle valve, solenoid valve, and Model # 45 Water Panel