PRODUCT DESCRIPTION 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 the home. INCLUDED IN THE BOX: Installation instructions and template, humidifier with built-in fan, 24 VAC transformer, manual humidifier control with sensor, saddle valve, solenoid valve, and Model # 35 Water Panel. FROM THE MANUFACTURER The Aprilaire Model 700M Whole-House Humidifier features a built-in bypass damper. The bypass damper is conveniently labeled for both summer and winter settings, allowing you to set it for the entire season with no guesswork involved. The Aprilaire Model 700 Whole-House Humidifier is simply the best performing bypass humidifier on the market.