I have an Aprilaire 700 whole house humidifier with a manual mode humidistat on the return. I noticed that the unit was draining water even when the heater/fan was off. Is this expected? I just hear it constantly draining, which I'm guessing is due to low humidity in the return? What's the point of draining when the fan is off?

Additional details: If I lower the threshold on the humidistat, I hear the solenoid engage (or disengage?) and the unit stops draining. There are no noticeable leaks. The only water I see is what comes out of the drain pipe.

  • what do you mean by draining?
    – jsotola
    Dec 5, 2019 at 3:31

1 Answer 1


Sometimes the moisture drains when the fans and or compressor is no longer running, we would to know more about your system, it could be a bad valve in the supply to the humidifier causing the water but more information is really needed to provide a positive answer.

  • What additional information do you need? Dec 8, 2019 at 17:26
  • Is it draining at the air handler? AC? Is there a flow or vane switch , if your ac coils are icing it may take several hours for the ice to melt, the humidifier should be controlled by a pressure switch or a vane switch that turns off the flow when the fan is not running, it sounds like a bad pressure/vane switch because it quits after turning it down, however I have seen icing blamed in the past when the humidifier was working correctly.
    – Ed Beal
    Dec 8, 2019 at 17:44

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