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Furnace Humidifier not Working? Replace it

Updated: Sep. 30, 2019

Replacing old furnace humidifiers with energy efficient ones is better than repairing them

FH12FEB_REPHUM_03-2Family Handyman
If the humidifier on your furnace is not working, you can easily fix or replace it yourself. Simply follow our step-by-step photos and instructions.

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Remove the furnace humidifier that’s not working

Photo 1: Disconnect and remove the furnace humidifier that doesn’t work

Remove the screws from the bottom of the old humidifier. Then unscrew the fasteners at the top. Tilt the top out and lift it off the duct or plenum.

Furnace humidifiers are pretty simple gadgets. When they Stop working, the cause is usually a clogged or burned-out solenoid water valve or a bad drum motor. You can replace those parts yourself—if you can find them at an affordable price. The price of the parts for a humidifier that’s 20 years old or older can be shocking. In that case, you may be better off replacing the entire unit with a newer and more efficient model. Many of the newer models come with a digital humidistat and automatic outdoor temperature compensation (such as the Honeywell No. HE 225 DG 115; about $153 from The compensation feature automatically dials down humidifier output as outdoor temps drop. That reduces any condensation on your windows.

If you can operate tin snips and read a wiring diagram, you can do the entire job yourself in about two hours.

Turn off the power to the furnace and humidifier. Next, disconnect the round bypass duct (if equipped) coming into the old unit. Then turn off the water valve and disconnect the old water line. Disconnect the wiring to the solenoid valve and humidistat and remove the old furnace humidifier (photo 1).

Add humidifier to furnace by installing the new furnace humidifier

Photo 2: Cut the new opening

Slice an opening into the new metal by hammering the narrow edge of a screwdriver into it. Then jam tin snips into the “slice” and cut out and along the edges of the trace. Leave the corners for last.

Photo 3: Install the bypass

Install the summer/winter damper (provided with the new furnace humidifier) and insert the bypass duct. Secure it with sheet metal screws.

Photo 4: Install the outdoor temperature sensor

Connect the thermostat cable to the outdoor sensor. Then push the extra wire back into the hold and caulk the hole. Mount the sensor to your house.

Refer to the installation manual and compare the new opening size to the old opening. If the new humidifier requires a smaller opening (most do), you’ll have to make an adapter plate. Cut a piece of sheet metal to completely cover the old opening. Attach it with No. 6 x 1/2-in. self-drilling sheet metal screws. Then trace the new opening onto the plate, making sure your lines are level. Cut the new opening (photo 2). Use caution to avoid damaging the A/C coil. Hook the bottom edge of the new humidifier onto the opening and tilt the top toward the duct. Level the unit and secure with self-drilling sheet metal screws. Then attach the bypass duct (photo 3).

Locate the new humidistat on the return air duct. Then run 18-2 thermostat cable to a shady non-south-facing side of the house for the outdoor temperature sensor. Mount the outdoor sensor (photo 4).

Connect the water line to the solenoid valve and hook up the humidistat wiring. Turn the power back on and test the entire system.

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • 4-in-1 screwdriver
  • Caulk gun
  • Cordless drill
  • Drill bit set
  • Hammer
  • Nut driver
  • Tin snips
You’ll also need gloves.