Forced-air humidifier
Date: 12-05-2013
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. [ citation needed ] 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.
The humidifier should usually be disabled during the summer months if air conditioning is used; air conditioners partially function by reducing indoor humidity.
Drum [ edit ]
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 ]
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 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 filters ( MERV ratings as high as possible to ensure small numbers of mold spores reaching the humidifier pan) when the water supply is turned on.
The humidifier should usually be disabled during the summer months if air conditioning is used; air conditioners partially function by reducing indoor humidity.
Drum [ edit ]
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 ]
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 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 filters ( MERV ratings as high as possible to ensure small numbers of mold spores reaching the humidifier pan) when the water supply is turned on.