Installing a standalone humidifier typically only requires that the user plug it in, while installing a furnace humidifier requires connecting it to the furnace's return duct by cutting out space for the humidifier's template. Furnace humidifiers also have their own ducting and plumbing components that must be attached.
Humidifiers are fairly small devices compared to other HVAC equipment, and humidity spreads evenly through rooms and homes without needing fans and ductwork. This, combined with their safety, means that there are plenty of standalone humidifiers on the market than have no special installation demands and easy maintenance. However, these systems draw a bit of power, and those using central heating may find a furnace humidifier provides better efficiency and lower operating costs.
A bit of plumbing knowledge is necessary to install a furnace humidifier. Automatic humidifiers need a connection to the water line, and water valves need to be put into position in a manner that doesn't cause leaking. Small mistakes can result in future problems, including water leaks into components of the furnace, so caution is due. After the drum is installed, it must be set to the correct water level to provide efficient water flow to the system. Manufacturer recommendations can help users optimize their newly installed system.