Parts

• A traditional drum humidifier includes a rotating wheel and a water reservoir housed in a metal drum. A removable sponge or pad attaches to the wheel, while a humidistat controls the amount of humidity the drum humidifier produces.
  
  

Operation

• A drum humidifier works on the principle of evaporation. As the rotating wheel turns, the sponge or pad receives constant moisture from the water reservoir. As the furnace sends warmed air into the drum unit, the air moves through the moistened sponge or pad. The humidified air then travels throughout the home's ducts.
  
  

Pros and Cons

• While drum humidifiers can effectively humidify a home, they create their share of annoyances in terms of maintenance. As the evaporator sponge or pad grows hard and non-permeable through repeated use it can block the passage of air through the unit. The water in the reservoir can then stagnate and host mold or bacteria.
  
  

Innovations

• Changes in drum humidifier technology have eliminated much of the downside previously associated with these units. These designs use rotating plastic discs instead of sponges or pads, which reduced the maintenance issues of the past.