I'm installing an Aprilaire 700M Humidifier in a Bryant 340MAV Furnace.

I looked up the furnace manual and it states:

A quick-connect terminal (HUM) and screw terminal (COM24-v) are provided for 24-v humidifier connection. HUM terminal is energized with 24v (0.5-amp maxi-mum) when gas valve is energized.

With that in mind, I assume I should wire it like this:

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My Question

  1. Is the wiring correct?
  2. The humidifier came with a 120v to 24v transformer. Do I need that since my "HUM" line is 24v?
  • I would say you got it right, no you do not need the extra transformer
    – Traveler
    Oct 10, 2022 at 18:56

1 Answer 1


Yes that connection is logically correct. Technically a person should also check the humidifier and determine how much current it'll draw for its solenoid valve and/or relay, then confirm that current is less than the 0.5A maximum your furnace control is designed to support.

If you happen to have a smart thermostat such as Ecobee or Nest and would want to let it control humidity for you as well (rather than use the stand-alone humidistat) that's also possible. In this case your red line would go to the thermostat's humidifier control terminal rather than the furnace HUM terminal. The blue wire would stay as-is.

  • Thank you for replying, in the "Specifications" listed in my humidifier manual, it says: Electrical Data: 24 VAC, 60 Hz, .8 Amp Do you think that .8 amp is close enough or cause for concern? Oct 10, 2022 at 19:37
  • I went ahead and hooked it up per the diagram in my question. All seems well Oct 10, 2022 at 21:45

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