Smart Furnace Humidifier Control

I finally did something my wife finds useful with the smart house. I have automated the furnace humidifier. It seems that every winter we were constantly adjusting the humidistat based on the outside temperature. Not any longer. It is now automatic.

Sensors Needed:

  1. Humidity. I used a Xiaomi Aqara humidity sensor coupled with bspranger’s device handler. It reports status every time the humidity changes 1%, or the temperature changes 1deg.
  2. Isolated Relay. I used a LINEAR FS20Z-1 Z-Wave 20-amp Isolated Contact Fixture Module.

Connections:
The circuit is pretty easy. The only WTF part is the relay I used supports up to 20amp on the switched side. Furnace humidifiers use 24VAC and tiny little wires. It just looks odd hooking up the tiny humidifier wires to the 12ga wires in the module.

Humidifier%20Circuit

Automation
The next part was to figure out how to control it. The humidistat has a chart attached.

Doing some basic algebra, you can see that the target humidity is 0.5T+25, where T is the outside temperature.

The next step was to program Webcore.

There are a few variables:

T = Outside Temperature (I get it from the accuweather app)
H = Humidity from the Sensor
HT = The targeted humidity from the equation
OS = Offset. I can use this to tweak the final value of the targeted humidity.

I also set up webcore to send me a notification every time the system changes state until I know it is working properly.

Since I had the wiring and electrical boxes lying about, my total investment was about $35.

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