Whole House Humidifier with Nest Thermostat

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Old 10-05-12, 02:03 PM
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Whole House Humidifier with Nest Thermostat

Nest has made a new thermostat which supports humidifiers and I have already put my pre-order in. I currently have the old nest thermostat connected to my 8 year old furnace using 6 wires (R, W1, W2, Y1, G, C). I have a 7th wire available which I hope to use to control my new humidifier. I have not yet purchased a humidifier because I am waiting to see what additional items I may need to purchase first.

What confuses me about the nest is that unlike most other controllers I have seen it only has one terminal for the humidifier. How do I wire it all together? My furnace does not have any 24v humidifier connections on it. Does this come into play? Does the humidifier pull power from the transformer in the furnace? Can my furnace handle that? How does the thermostat control the humidifier with just one wire?

I do not yet know if the new nest is smart enough to run the humidifier only when the furnace is running. I tried calling nest support and they were completely unable to help me.
 
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Old 10-05-12, 09:09 PM
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Nest is pretty tight lipped in all actuality when it comes to this new stat and wiring. They recommend using one of THEIR contractors..... Anyway enough of my rant about NEST. You wiring will depend on exactly which humidifier you purchase. I would need to know that first. Most likely NEST is sending a 24V signal to operate the humidifier. This will use the furnaces transformer. Your furnace transformer should be able to handle this load. I, however, do not like or recommend installing this way but it can be done. SO, basically one side of solenoid connected to C the other connected to * on nest. Or you can add an isolation relay and a 15VA transformer. What is the make and model of your furnace?
 
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Old 10-05-12, 10:36 PM
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My furnace is an American Standard AUD100R948K5.

I have not yet purchased a humidifier. I was waiting until I have all the facts. Any suggestions?

Also, could you expand on why you don't recommend installing this way?

Thank you for your help.
 
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Old 10-05-12, 11:15 PM
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I am going to answer some of my questions with the following link.

Nest | Nest Certified FAQ

It looks like nest is starting to give out some information. Look at the very bottom of the page. It has a wiring diagram.

My question now is what exactly is the "required relay". Is this the "isolation relay" you are referring to? Do you know an exact brand and model number of what I need?
 
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Old 10-06-12, 06:34 AM
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The schematic depicts a required relay using a pre-installed humidifier that has 2 wires going to an old thermostat already.

I dont like wiring humidifiers to use the furnace transformer. If something happens to the solenoid or humidifier wiring that causes a short it will take down your furnace as well and then you have no heat. That is the reason I always choose to use a dedicated transformer for the humidifier circuit.
 
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