Nest's wiring with humidifier

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Old 11-14-15, 01:10 AM
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Question Nest's wiring with humidifier

I've recently bought the Nest thermostat. The installation starts smoothly until I notice that my former humidifier use two wires instead of the recommendation of one. Nest officially suggests looking for their paid specialist to aid the process while I'm decided to go to the Internet for help. However, due to my lack of knowledge in relevant area as well as for the consideration for safety, after some research it seems better to ask for help directly.

Here is the information of my hardware devices:
- thermostat/humidistat: Nest gen. 3
- humidifier: GeneralAire Model 1042LH
- former humidistat: random honeymoon model (see photo)


The heating system is tested and works as expected, while the two of the humidifier wiring really puzzled me. They are not labeled either on the former stat or over the connection to the humidifier.





As showed in the photo, the black one on the right which is connected to a dial panel, along with the left one which eventually turns white, go through the furnace and up to the wall. The question remained is what particular wire each respectively serves and how am I suppose to connect them with the stat.



In case it is informative, there's also a switch labeled as 'fan' beside the furnace, maybe it has something to do with the fan wire I saw over other posts.

I'm also wondering what exactly do the dial and the switch do out of curiosity.

Any of your help is appreciated!
 
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Old 11-14-15, 01:23 AM
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Welcome to the forums.

A approved your thread as you are a new member and had many pictures in it.

The wiring will be very easy.
Do you have the nest connected to your furnace using a C connection ?
If you don't..... you should.
 
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Old 11-14-15, 07:55 AM
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The knob sets the humidity level and the switch looks to control the fan if you can believe what the switch says. That may have been added to run the blower when there was no call for heat or cool.

You will no longer be using that honeywell h'stat.

Your humidifier solenoid valve has two black wires on it. One will go to the C terminal at the furnace control board and the other black wire connects to the * terminal on the nest.
 
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Old 11-14-15, 01:17 PM
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Thx for your reply

My old thermostat only uses W and RH wires, and the C wire from the solenoid goes directly upstairs. Does it mean that I need to open my furnace, look for the control board, and wire the C terminal with the solenoid and my Nest?

Also, if I have a stand alone stat, why is there a knob that do the same job?
 
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Old 11-14-15, 04:51 PM
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Your humidifier solenoid valve has two black wires on it. One will go to the C terminal at the furnace control board and the other black wire connects to the * terminal on the nest.
This is what you need to end up with. Regardless of how you do it.


The C wire from the humidifier to "upstairs" can be used for the * connection but you'll still need a connection to C at the furnace.

Also, if I have a stand alone stat, why is there a knob that do the same job?
You have a standalone stat NOW. Now you no longer need the separate humidistat. The nest will control the humidifier directly.

You will also need to tell the stat in programming that you are using a humidifier with a call for heat.
 
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Old 11-16-15, 08:05 PM
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Then the wired part is that the humidistat was always there even when my old stand-alone stat was fully functional. I can't really tell whether it is bypassed or not but it seems to be connected. Does series connection hold compositive effect under such circumstances?
 
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Old 11-16-15, 08:38 PM
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You can either turn the standalone h'stat all the way to maximum humidity or take the two wires off of it and wire nut together..... eliminating that stat completely.
 
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