How to Repair a Furnace Humidifier With Not Enough Humidity

Turn up the humidifier's humidistat if it is not set high enough. For some units, the humidistat will be separate from the humidifier, located on a central wall in your home or integrated with the furnace's thermostat. For others, the humidity level can be adjusted with a knob on the humidifier itself. Turn up the humidity level if possible and wait to see if that corrects the dry air problem.

Power off the furnace and humidifier and disconnect both from their power sources. Inspect the humidifier and its power wire to ensure all components were properly reassembled after the previous winter. If it was unplugged, try plugging the unit in and testing it. If the unit's power wire is cut or fraying, contact a heating and cooling specialist to replace the wire.

Check the humidifier's water inlet valve. Furnace-mounted humidifiers have water sources that can be shut off like a hose, and the valve might be sticking out from the wall behind the furnace or attached to the unit near the water inlet. Open the humidifier's water valve if it is closed.

Check the unit's water reservoir to see if the level is too low. If the water is too low, fill the reservoir with cool, clean water.

Open the humidifier's bypass damper if it is closed. This is a large valve that allows air and humidity to pass out to the home from the furnace. Over the summer, this damper could be intentionally or accidentally closed, preventing airflow once winter arrives. In addition, some machines have internal controls for the bypass damper that could malfunction and stick closed.

Remove the unit's evaporator panel or pad and check for debris, residue and other materials that could clog it. This piece of the humidifier is typically located near the top of the unit, and air is blown through it while it is damp to humidify the air. If the panel or pad is clogged, clean or replace it.

Plug the humidifier and furnace back in, power the units on and test to see if the unit is now working properly. If it does, monitor it during the season in case the problem reoccurs. If not, contact a heating and cooling specialist for assistance.