Wiring T10 Thermostat to Aprilaire 400 Humidifier

TheBeholder1805

I would like to install a Honeywell T10 thermostat to control my Aprilaire 400 humidifier. Right now the humidifier solenoid is connected to the furnace as shown in the pic so that it only runs when the heat is on. Do I need to run a wire from the furnace up to one U slot on the T10, and then run another wire down from the other U slot to the solenoid? Or since the T10 is already powered and already knows when the furnace is on, can I just run a single wire from U to the solenoid (and switch the U slider up)? Basically, can I get rid of the red wire in the diagram and replace the humidistat with the T10?

Current wiring diagram and photo: https://imgur.com/a/wMAoai6

HVACNUT

There's no humidistat in the return?
Is that in an attic, with no emergency pan and safety switch?

That's a bypass humidifier and should only run during a heat call. It should be wired through a humidistat, and a fan proving switch, or through the HUM terminal on the furnace board. 

One side of the solenoid must be Common. On the T10, move the U jumper to the UP position, and use the upper U to power 24 volts to the other side of the solenoid. This is only if the humidifier is using the furnace transformer. 

TheBeholder1805

HVACNUT said:

There's no humidistat in the return?
Is that in an attic, with no emergency pan and safety switch?

That's a bypass humidifier and should only run during a heat call. It should be wired through a humidistat, and a fan proving switch, or through the HUM terminal on the furnace board. 

One side of the solenoid must be Common. On the T10, move the U jumper to the UP position, and use the upper U to power 24 volts to the other side of the solenoid. This is only if the humidifier is using the furnace transformer. 

The humidistat is in the return. It’s near the top of the diagram but it’s physically to the left of the furnace in my crawlspace. The humidifier is using the furnace transformer so it sounds like I only need the one U wire. Thanks!

pecmsg

Humidifiers should use a seperate transformer.