Editing Humidifier (section)

=== Drums ===
Drum style (bypass) uses a pipe to bring water directly to a reservoir (a pan) attached to the furnace. The water level in the pan is controlled by a [[float valve]], similar to a small [[toilet]] tank float. The wick is typically a foam pad mounted on a drum and attached to a small motor; hot air enters the drum at one end and is forced to leave through the sides of the drum. When the [[hygrostat]] calls for humidity, the motor is turned on causing the drum to rotate slowly through the pan of water and preventing the foam pad from drying out.
:Advantages include:
:* Low cost
:* Inexpensive maintenance (drum-style pads are cheap and readily available){{Citation needed|date=November 2007}}
:Disadvantages include:
:* Requirement for frequent (approximately monthly) inspections of cleanliness and pad condition
:* Water evaporation even when humidification is not required (due to the pan of water which remains exposed to a high [[velocity]] air stream)
:* [[Mold (fungus)|Mold]] growth in the pan full of water (this problem is exacerbated by the large quantity of air, inevitably carrying mold spores, passing through the humidifier whether in use or not).

For the latter reason especially, drum-style humidifiers should always be turned off at the water supply during summer (air conditioning) months, and should always be used with high quality furnace [[air filter]]s ([[MERV]] ratings as high as possible to ensure small numbers of mold spores reaching the humidifier pan) when the water supply is turned on.