The aprilaire 600 unit works by taking air that has been heated by your furnace and passes it through a panel that has a small quantity of water running across it. The water panel looks a little like a radiator. The water around the panel evaporates into the hot air and gets distributed via your existing ductwork. That’s it, nothing fancy. Note that, just like any humidifier, the unit is more effective if you connect it to hot water rather than cold.