I have Honeywell Humidifier HE225A, Honeywell Thermostat TH6110D and Honeywell Humidistat H8908B all installed already. Now my Humidifier runs 24/7 wasting water because it is connected with the furnace blower fan cycle which is on 24/7. How can I wire it so that it only runs during the heat cycle.


There should be a terminal on the board of the furnace supplying either 24v or 120v. Usually marked hum. That's where you pick up power for the humidifier.

For like 20 years I've been wiring the humidifier from W to C without a single issue. On a call for heat W is energized if the humidistat is calling the humidifier energizes and compleats to common.

  • Post a picture of the board if you're not sure which terminals to use. – Platinum Goose Mar 18 at 22:08

Why are you running the fan 24/7? If you switch the thermostat fan switch to auto you will get the result you are looking for. I sometimes recommend constant fan for cooling or air filtration but not for heating. If you are on 24/7 because some rooms get too cold when using auto, balance the airflow. My method is open all dampers then close outlets starting at 1/4 closed in the too hot rooms. You might need one setting for cooling and another for heating. Common problem in 2 story colonials. With a magic marker mark each damper coming off the main ducts with an H and C. Aprilaire has a stat with an intermittent fan setting. If you think you have a wiring problem see: https://www.manualslib.com/manual/69853/Honeywell-H8908b-Humidistat.html?page=3 It shows the 3 methods of integrating the humidistat. In lieu of the seasonal changes you could also add a zone damper system to eliminate the hassle.

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