the reservoir. However, boiling water requires significantly more energy than other techniques. The heat source in poorly designed humidifiers can overheat, causing the product to melt, leak, and start fires. Ultraviolet germicidal irradiation (UVGI) Some humidifiers have an integrated ultraviolet germicidal irradiation (UVGI) feature. Water ionizer Some humidifiers have an integrated water ionizer. Maintenance A torx screwdriver is often needed to open consumer electronics. Humidifiers with a centrifugal fan may become noisy due to build up which cannot effectively be removed with vinegar for example. However, the fan can be replaced, and the model name of the fan and its specifications can be figured out by disassembling the humidifier and detaching it. Fixed-installation humidifiers For buildings with a forced-air furnace, a humidifier may be installed into the furnace. They can also protect wooden objects, antiques and other furnishings which may be sensitive to damage from overly dry air. In colder months, they may provide modest energy savings, since as humidity increases, occupants may feel warm at a lower temperature. Bypass humidifiers are connected between the heated and cold air return ducts, using the pressure difference between these ducts to cause some heated air to make a bypass through the humidifier and return to the furnace. Any humidifiers should usually be disabled during the summer months if air conditioning is used; air conditioners partially function to reducing indoor humidity, and having a humidifier continue to operate will waste significant amounts of energy. 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) 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 growth in the pan