IAQSource.com > Articles > Whole house humidifier maintenance tips

Whole house humidifier maintenance tips

Although the steam humidifier may be making a comeback - the "flow through" variety of whole house humidifier is the most pervasive throughout homes in the United States.  This article offers a quick overview of flow-through humidifier operation and some easy-to-follow maintenance tips.

How whole house humidifiers are supposed to work . . .

When the humidistat is calling for humidity (and the furnace is running) a solenoid valve will open and allow fresh water to flow across a porous evaporator pad.  The water supply starts from a saddle valve attached to a water pipe.  Water flows through 1/4" copper tube to a solenoid valve equipped with an inline water strainer.  The valve electrically opens and closes to control the supply of water, and the strainer filters particles from the water.   Filtered water  then goes through the orifice which meters the water through a 1/4" feed tube (usually plastic) to the water distribution tray.  From the distribution tray,  water flows by gravity into the water panel evaporator (sometimes called a "filter pad") where part of the water is evaporated and enters the home's air supply ducts.  Once the pad is saturated, the overflow water flushes the majority of minerals left after evaporation off the water panel pad.  The water drains via a 1/2" drain tube through a drain spud at the bottom of the humidifier.


A flow-through humidifier is a relatively simple piece of equipment.  The only real "moving part" is the solenoid valve, which opens to allow water flow to the humidifier.  Still, flow-through humidifiers do need occasional maintenance.   More often then not - our customers contact us after their humidifier has been neglected for several years and is leaking

Maintenance Tips:

Change your water panel.  The typical water panel (or evaporator pad, or filter) in the humidifier is constructed of an expanded aluminum honeycombed mesh dipped in a ceramic slip (liquid clay).  The large surface area of the clay material is perfect for absorbing water.  When openings in the water panel become clogged with scale and mineral deposits, they will restrict airflow through the pad and should be replaced.  The life of the water panel evaporator will vary with the hardness of the water, the amount of use, and the application.  Is ins recommended that the water panel be changed at least once every year (twice a year for the Aprilaire model 400).  The water panel with be most efficient when installed with the spot at the top.  Make sure the entire water panel is enclosed in the scale control insert (frame).

Make sure unit is level.  The unit or distribution tray must be level so that water will be evenly distributed over the entire width of the water panel evaporator.  If the full width of the water panel is not wetted, the capacity will be reduced.

Clean the orifice.  The orifice is a metering device that regulates the amount of water flowing through the feed tube to the water distribution tray.  The orifice typically nests into the waterline directly after the solenoid valve.  If the orifice is blocked with scale - gently insert a fine needle through the small opening.  Aprilaire orifices are color-coded and made especially for certain model humidifiers.

The blue orifice is used on models 350, 360, 440, 700, 760, 760A and 768
The red orifice is used on models 112 & 224
The yellow orifice on models 400, 500,  550, 550A, 558, 560, 560A, 568 & 600
The white orifice used on models 110 & 220

Purchase a maintenance kit.  If it has been many years since a humidifier has been maintained - it may be the path of least resistance to replace several of the humidifier parts that are likely to be worn out or covered with scale.  A maintenance kit will often contain water panels, a feed tube assembly (with strainer and orifice), a scale control insert, a water distribution tray and a drain spud.

Lastly  - Close the seasonal damper in the summer months!!