Inspect your humidifier's evaporative elements once a month during the heating season and replace them at least yearly. The evaporative elements will pick up minerals from the water, and their constant exposure to hot air will dry them, reducing their capacity to absorb and hold water.
Drip-style humidifiers require less cleaning because the flow of water over their surfaces helps prevent mineral deposits and mold from forming. Drum-style units need more attention because the drum is more likely to develop mold. If the evaporative element is serviceable and not caked with minerals, you can wash it in a mild dish-soap solution. Rinse it well and replace it.
About a half-hour or less to replace the evaporative unit, more if scale cleaning is required
Wrenches, screwdriver, old kitchen knife
Removing access plate, replacing simple evaporative units
Turn off furnace power and humidifier water supply
Replacement evaporator units, pipe cleaner
Using the tabs as indicators, lower the disk wheel into the V-guides on the inlet and motor plates. Make sure that the inlet end of the axle is seated in the bearing at the bottom of the V-guide and that the gear on the other end of the axle is engaged with the motor gear.
To remove an evaporator element, slide your fingers under the unit and lift it out. If it's heavily scaled, pry it out gently with an old kitchen knife. Be careful, as hardened mineral scales can be sharp. Remove the distribution tray if present.