The Herrmidifier 500 atomizing humidifier is a self contained cold steam humidifier unit. It is typically hung from the bottom of the return air ductwork so it injects cold steam into the duct system. It can also be set on a table or shelf in the conditioned space. This second applicaton is common for humidors across the planet. The Herrmidifier 500 was replaced by the Herrmidifier 707U recently. If you are replacing the model 500 with the model 707U you will need to reuse the dome cover (part #12A1) and spring clips (part #41) from your old unit OR purchase new ones since the model 707U does NOT include them. Periodic maintenance on this device consists of taking it apart and cleaning it.