Furnace Humidifier Control

I am thinking of controlling the humidifier mounted on my furnace. There is a humidistat in the cold air return duct that controls a 24VAC furnace signal to the humidifier. Basically, I want to replace the humidistat with a zwave or zigbee switch that would turn the humidifier on/off based on readings from a zwave humidity sensor in the living space. I am envisioning a battery operated open/closed (normally open) switch. The switch would be carrying the 24VAC signal. Is there a sensor ouot there that I can repurpose for this? Has anyone done this?

You could use an esp micro with STAnything.

I was planning on doing that but just haven’t gotten around to implementing it.

My Ecobee 3 thermostat does this perfectly without any extra effort. The only requirement is having the 2 wires from the humidifier running to the thermostat location. It also integrates with SmartThings, Alexa, etc.


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No way to get wires to the thermostat wothout tearing out the drywall ceiling in the basement. I was hoping to be able to read the thermostat state (Honeywell RTH6500) with the ST app, and use it to control a smart plug. I can turn the thermostat on/off, etc. with the ST app, but it doesn’t report if it is in heating, cooling, etc.

So, my current throught is to use a Centralite humidity sensor and a NuTone Isolated Fixture Controller to control the humidifier. The way I envision it working is:

  1. Humifier power provided by the furnace (24VAC).
  2. The NuTone controller will turn on/off the controller, replacing the humidistat that is on the cold air return.
  3. The Centralite humidity sensor will drive a WebCore piston that turns on/off the humidifer (via the NuTone controller) based on the outside temperature (Accuweather smart app), furnace operating mode (heating only), and interior temperature.

The parts I am planning on buying are:

Humidity Sensor: https://www.amazon.com/dp/B07BSXX5TD/?coliid=I1HZENQGUQMEPP&colid=2K8ZHAHTU9RAA&psc=0&ref_=lv_ov_lig_dp_it

NuTone Relay: https://www.amazon.com/dp/B00WXLRF2U/?coliid=I3D9159EXCH5PQ&colid=2K8ZHAHTU9RAA&psc=0&ref_=lv_ov_lig_dp_it

Anyone ever tried anything like this?