Whole House Humidifier System

HVAC humidifier system

The humidifier system of a whole house furnace requires periodic cleaning and maintenance to stay running properly.  In the winter time, during the driest time of year, a furnace’s humidifying system becomes one of the most important parts of the overall HVAC system.  Water from the house’s water supply injects into the dry air produced by the furnace, resulting in healthier, less dry air in the home.

In order to transfer the moisture to the air without wasting excess water, the humidifier must work properly.  A clean humidifier system also promotes healthier air quality.  Since a humidifier system typically bypasses the HVAC filter, any contaminant, such as mold in the humidifier transfers throughout the home.

Humidistat controller

Steps for Inspection and Repair of a Whole House Humidifier

Step 1:  Locate the humidistat controls on the humidifier system.  The humidistat controller monitors the relative humidity in the air.  It is typically located at the cold air return of the furnace box.  Some humidifier systems are installed in an interior wall of your home separate from the furnace.  Turn up the humidity setting all the way up to 100%.  This forces the humidifier to release water into the system.

Step 2:  Turn the heating system on at the thermostat.

Step 3:  Go back to the furnace and listen for water running through the humidifier.  Let the system run for a few minutes, but do not allow it to overflow.  The excess water exits to a drain in the floor.  Make sure the water is draining correctly and not leaking on the floor.

Step 4:  Shut off the furnace at the thermostat and turn off power at the fuse panel.  When working around water that is near an electrical device, safety is important.

Humidifier with removed cover

Step 5:  Remove the humidifier cover.  The humidifier is typically a bypass duct line located in the front or side of the furnace in the cold air return.  Interior wall humidifiers are separate from the furnace.

humidifier bypass valve

Step 6:  Inspect the bypass duct.  The humidifier system generally has a shut off lever.  In the summer time, close off the humidifier bypass line so no addition moisture contributes to the output air.  In the winter, open the bypass line to allow air flow through the humidifier system.  For interior wall humidity systems, there is no connection to the furnace.  These systems use their own fan instead of the air from the furnace blower fan.

humidifer evaporator pad removed

Step 7:  Inspect for water inside of the humidifier.  After running for several minutes, water is typically present on the evaporator pad media and the water distribution tray in a system in good working condition.  If there is no moisture present, there is a problem with the water supply.  Either the low voltage water solenoid valve is not working properly or the water supply line is damage, clogged, or shut off.  Alternatively, if the water is still running after the system is shut off, the solenoid valve is in need of repair or replacement.

Humidifier water distribution tray

Step 8:  Inspect the evaporator pad media.  The evaporator pad provides a greater surface area of water so more water transfers to the air.  The materials in the evaporator pad can deteriorate over time.  You may see calcium or lime build-up collect on the evaporator pad.  If it falls apart easily or is heavily corroded, then it is time for replacement.  Replace the evaporator pad media once per year.  In between replacements, use a mixture of 50% water and 50% white vinegar to clean the media with a scrub brush.  Wash the evaporator media thoroughly with clean water after scrubbing.   The top of the water distribution tray typically has a distribution separator for the flow of water from the supply line.  Make sure that the separator tray is clean so the water can fully flow though on the evaporator media.

Humidifier water supply line
humidifier water solenoid valve

Step 9:  Check the water line.  Step 7 verified the water flow through the system.  To increase the moisture in the air of the home a proper amount of water must flow through the humidifier system.  Verify that a consistent amount of moisture is present on the evaporator pad.  Typically some amount of extra water will flow through to the drain.  Additional water is needed, but too much water is wasteful.  Adjust the water flow until the right amount of water is flowing through the system.  In generally most standard size systems use about 4 gallons of water per hour at a supply pressure of 60 P.S.I., when running.   This amount varies, based on the size of the furnace and the size of the humidifier system.