Another humidifier with Nest install question

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Old 02-21-17, 08:37 AM
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Another humidifier with Nest install question

I just got an Aprilaire 700 automatic humidifier for my Arcoaire N9MSB that has a 24VAC connection for a humidifier on the board. I have 18/5 ran for the Nest right now. I've currently got it hooked up with the Nest using the wiring diagrams I've found here and on the Nest Pro install. I also do not have a Common hooked to the Nest anymore since I stole that C wire to go to the * on the Nest. However, there are two diagrams for a powered humidifier and I'm not sure which is the preferred method. One install is without a relay and the other is with a relay. I have purchased the relay just to be safe, but is the only point of the install with the relay is if the HVAC system doesn't have a HUM terminal to trigger the humidifier? I'm hooked up as pictured below.

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Old 02-21-17, 08:53 AM
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Welcome to the forums.

You wire it exactly like the brown wires show. Disregard the blue C wiring.
One brown wire goes to C at the furnace.
The other brown wire goes to the * terminal.

A HUM terminal is not required or needed.
 
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Old 02-21-17, 09:09 AM
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OK gotcha. Thanks. From the way I was reading the furnace manual, the HUM terminal was required to activate the humidifier with heat. I guess the Nest controls that with it wired as pictured? What is the HUM terminal used for them? And why is there one diagram with a relay?
 
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Old 02-21-17, 09:13 AM
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And I had one brown wire off solenoid to the HUM terminal and one brown wire to the C on the furnace board. It was working that way but these diagrams were bugging me thinking about them.
 
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Old 02-21-17, 09:17 AM
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The HUM terminal is utilized with a manual humidistat.

In your case the nest controls the humidifier directly.
In it's programming you can tell it when to activate..... with heat is the most economical.
 
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Old 02-21-17, 09:26 AM
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Not sure what you mean by "powered" humidifier. I think your talking about the current sensing relay which is only required on the 700M. I think the way you have it wired will work.
 
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Old 02-21-17, 09:52 AM
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By powered I mean it has an onboard fan. That's just the nomenclature used in the Aprilaire literature.
 
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Old 02-21-17, 09:56 AM
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I show that the two grown wires on your unit require 24vac to be applied to them to activate the solenoid and the internal fan.

On some of the very early models...... the two wires were only required to be shorted together to activate the solenoid and fan.
 
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Old 02-21-17, 10:14 AM
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So are you saying that one needs to be connected to the HUM terminal for 24V or am I good with it hooked up according to the diagram?
 
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Old 02-21-17, 10:22 AM
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Follow the diagram....
Your nest will supply the needed 24v from the * terminal.
 
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Old 02-21-17, 10:34 AM
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Roger that. Thank you sir
 
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