Adding humidifiers to a home is a good way to up your sales while also providing a great service to your customer. There are of course many furnaces and air handlers and thermostats for that matter. So below are a few ways we have helped hook up humidifiers. 

Wiring Option 1:

Use the 24v Hum terminal. You can use this given your humidifier solenoid is 24v. Place a field wire from the 24v Hum terminal to one leg of your humidistat. Then from your humidistats other leg, wire to your solenoid valve. Then run the other side of your solenoid valve to 24v Common.

Wiring Option 2:

Use the 115v Hum, or EAC terminal on the furnace board. This will rely on the use of a transformer. Most humidifiers will come with them for this. Wire in the 115V side of transformer to the  HUM or EAC  terminal and to neutral. Then off the 24v side of transformer, place a wire from the 24 volt hot to the leg of the humidistat and then from the other leg of the humidist at go to one side of your 24 volt solenoid on the humidifier. Then with the other wire off the solenoid go to 24 volt common on the transformer. 

Wiring Option 3:

Use a thermostat that has built-in humidity control. This option usually works best because the humidity reading is from the actual space instead of just the return duct. For this you will need a wire running depending on the thermostat used. So you would wire in at the thermostats humidity terminal. This is different on some thermostats, Nest has a "*" terminal and ecobee has an "ACC" terminal and Honeywell you would assign a "U" terminal. So the wire from the humidity terminal would then go down to the 24 volt solenoid of the humidifier and then place the other wire from the solenoid to the 24 volt common. 

View or Download attachments for the most common humidifier wiring diagrams.