Nest Learning Thermostat Gen 4 - Connecting Humidifier - Requires Nest Pro to Configure for $160

[sld311]

So..  Just purchased the  Nest Learning Thermostat Gen 4 for the "specific" purpose to control my home humidifer.  I install the thermostat including the humidifier wire, configure the app, but can not configure the app to control the humidifier????  Spend "hours" with Nest support.  After pulling the Nest Pro manual from a website, I come to learn that I need to now "hire" a Nest Pro to come to my house and enter a special 6 digit code to allow that person to configure the thermostat for humidification???  So now in for $500?

I am reaching out to see if there are any other known options?

Otherwise returning thermostat...

Thanks in advance for any guidance.

[CoolingWizard]

When adding external devices such as a humidifier, there are different configuration setups that come up into play.

For example Does your humidifier have a separate humidistat? If so, can it be overridden or deselected? Can it be  controlled externally by a remote humidistat?

Does the Humidifier require a dedicated power supply? Or will a power sharing problem present itself? 

Many humidifiers are designed as standalone and independently controlled devices.  While they may allow remote thermostats connections, these connections are typically so the humidifier can turn on the blower fan itself. 

AC Cooling Wizard

[RobertRak]

On this forum, I have found that you are one of the most knowledgeable people who could help me with the following questions.

I want to connect my Aprilaire Model 700 humidifier directly to my new Google Nest Learning 4th Gen Thermostat using the AQ+ and AQ- connectors without any additional hardware or wiring. However, Aprilaire support informed me that this connection must be made using a "Dry Contact," meaning no voltage can be delivered from the thermostat to the humidifier.

While I have found various online references stating that this can be done, I would like to be certain and know all the steps required ahead of time.

To set up the AQ+ and AQ- connectors as "Dry Contacts," I understand that I need to:

1. Complete a factory reset.
2. Define the AQ+ and AQ- connections as a Humidifier.
3. Correctly set up the connections with the proper relay settings.

Is this correct, and are there any additional steps I need to take to make this work?

Thank you for your support!

Robert

[Lewy]

I’m on the same page. The reason why I bought nest 4th gen was to get all control in one unit 

Did someone help you?

[sld311]

Good news.  We are now up and running!

I did schedule an appointment with OnTech.   The Nest Learning Thermostat Gen 4 was new to this team and basically we spent the next 2 hours learning together.  (Side Note: They were not aware of NestPro menus and codes nor was it needed).  

We basically completed the following steps to connect my Aprilaire Model 560 humidifier:

• Connected humidistat wires to AQ+ and AQ- 
  • I was hoping to upload pictures, but do not have permission

• Initiated a Factory Reset to bring back the setup menu.   A full factory reset may not be required, but it is what I did so that I could reconfigure the wiring.

• During the setup process, there is a step to select which wire connections are used.  You will not see the AQ+ or AQ- in the base setup screen.  You will need to check the "Other" box to display the AQ+ and AQ- connections.

• As you continue through the setup process you will have the option to configure the AQ+ and AQ- as a humidifier.  From there you should see the "Humidifier" show up under the Thermostat / Equipment area.    You should also see Humidifier show up on the AQ+ and AQ- under the Thermostat / Wiring menu.
• Temperature Preferences Menu:  In this menu you will see the "Humidity Helper" option.  If you select this you will have the option to enable "Smart Humidification" which automatically adjusts humidification based on outdoor weather.

Hope this helps!  Please respond with additional questions...

[CoolingWizard]

@sld311, Thank you so much for providing the information you learned.  There is one minor correction needed.
The Nest Thermostat has built-in ability to measure the indoor humidity.  There should be a setting to specify your desired indoor humidity.  The HVAC industry, if you will, have determined the optimal winter humidity to be 50% at 75°F. Personally I prefer 40%.  To some people this may seem like a rather high humidity, however, in order to feel the heat in the winter time, you do need to have the moisture in the air. It also prevents the dreaded static electricity problems of it being too dry air. 

AC Cooling Wizard

[Elderpine]

Thank you so much for this post @sld311 !!! Choosing “Other” and then AQ+ and AQ- during setup ended a 3 hour battle getting this to work.  I was doing the setup on my phone and totally missed the additional wiring options below the fold!   You’re a lifesaver!

[Flyer88]

@sld311 You've given me hope. I had my furnace and a/c replaced with Goodman equipment but left the Carrier humidifier in place. I later discovered the technician didn't fully connect the humidifier.  

If I connect the AQ+ and AQ- to the 2 wires coming from the humidifier solenoid should that be all I need aside from redoing the setup in the Home app?  Right now the black wire from the solenoid goes to a plug in the furnace and the white wire is just disconnected. 

Also, I currently have 5 wires at the thermostat. How does this compare to your new configuration?

Y1 cool

W1 Heat

G Fan

C 24v Common

Rh Power

I'm suspecting I might need to run an additional 2 wires which would be a challenge.

Thanks!

[sld311]

@Flyer88 So just an update on my AQ+ and AQ- configuration suggested by OnTech.  After a few days I noticed that the solenoid valve on my Aprilaire 560 was "chattering" which is typically not a good sign and ultimately ended up damaging the Nest Thermostat.  Fortunately  OnTech refunded their service charge and I was able to exchange the Nest thermostat.  I "suspect" that the Nest Thermostat was not able to support the solenoid current draw??  I really don't know because difficult to find any good "circuitry" information for the Nest Thermostat.

So digging deeper I found this very helpful resource.

http://support-assets.nest.com/images/pro-faq/Nest-Pro-Installer-Guide.pdf

So after reading the manual above I ended up with a configuration very similar to that shown on the top of page 35 titled "Built-In Humidifier System, 2 Wire" but slightly modified where the HUM2 is actually connected to "common".  Since I can't seem to figure out how to add pictures, I will try to describe where I started with my original furnace configuration and where I ended final installation.

Original Furnace Configuration

My furnace had a HUM output that would turn on when the burners ignited.  If the house humidity was below the Humidistat setting, this circuit would power up and turn on the Aprilaire 560 solenoid valve.  So my circuit to run the Aprilaire 560 solenoid valve was:

Furnace HUM to Humidistat to Aprilaire 560 Solenoid Valve to Furnace COM

New Furnace Configuration

Because I am concerned that the Nest Thermostat may not be able to handle the Aprilaire 560 solenoid valve current, I created a configuration very similar to that shown on the top of page 35 titled "Built-In Humidifier System, 2 Wire"..   I also installed a White Rogers 90-290Q 24 VAC relay as suggested in the manual.  So I created the 2 circuits below.

Control Circuit (Low Current)

This side of the circuit turns the White Rogers 90-290Q relay on and off.  This circuit is configured as follows:

Nest * to White Rogers 90-290Q Relay to Furnace COM

When the Nest Thermostat calls for Humidity it activates the Nest* output (24VAC) and, in turn, energizes the White Rogers 90-290Q relay

High Current Circuit

This side of the circuit runs the solenoid and is configured as follows:

Furnace HUM to White Rogers 90-290Q Relay to Aprilaire 560 Solenoid Valve to Furnace COM

So this circuit will activate when HUM is ON AND  when the Nest* is ON which energizes the White Rogers 90-290Q Relay 

So high level.. The Thermostat turns on Nest * -> Energizes White Rogers 90-290Q Relay ->  Enables current to flow from Furnace Hum to AprilAir 560 Solenoid Valve

Additional Notes

• Nest Configuration (AQ+/AQ-/*)
  • I ended up configuring the Nest* output for the humidifier..   I am pretty sure you could also configure AQ+ and probably AQ- for the humidifier, but I just went with what was shown in the manual in this case.
• Thermostat Wiring
  • I am using the connections listed below.  Very similar to yours, BUT my system does not use the Common (blue wire on my system).  It is also not connected at the Furnace controller.  From my understanding some furnace / thermostat systems use the Common and some do not??  Not sure why.
  • And of course I also use the Nest* now to control humidity.

Y1 cool

W1 Heat

G Fan

C 24v Common

Rh Power

Nest* Humidity

• Your Furnace and Humidifier Wiring
  • I wish I were more help here....  I would "guess" that your black wire coming out of the furnace is very similar to my Furnace HUM output.  If I were to guess this black wire outputs 24 VAC relative to your Furnace Common.  You could use a voltmeter to confirm 24VAC between the black wire and your furnace COM which is what I did...  Keep in mind that this black wire may not energize at the same time your furnace turns on.  My HUM output didn't turn on until the burners turned on...
  • If so my configuration describe above will likely work for you

Sorry for the long dissertation, but tried to give you the detail to help you make the best decision possible... 

Good Luck!  And I will try to answer follow up questions.

And maybe @CoolingWizard can provide additional guidance...

[Flyer88]

@sld311  Wow, that's a lot of detail and very much appreciated.  You've helped me get a much better understanding about how this works, especially with the Pro manual.  It also uncovered some questions that I need to ask the technician that installed the furnace.  If the C wire isn't really needed on my setup then it would free up the wire I need for the humidifier control.  There's always a chance he connected it as the C just because it was available.  It's a bit of a longshot but better than trying to run another wire.  The black wire going between the humidifier solenoid and the furnace controller is also connected to C, but I did find the unused DH connector on the furnace.  That seems to match up with the wiring diagrams on page 35 that you pointed out.

So now I guess it's ask-the-installer time to see if I have an option to stringing another wire.

Thanks again!

[Elderpine]

Fantastic detail - thank you!

Here’s the 4th Gen Pro Manual in case it’s helpful:  https://tssassociatesinc.com/wp-content/uploads/2024/11/Nest-Learning-Thermostat-4th-Gen-Pro-Install...

[Nexusis]

Anyone else have issues with the T4 not updating the RH level based on outdoor temperature? It is enabled in the app but never updates. I’m having to go in the app to manually update the RH level when the temp drops

[CoolingWizard]

@Nexusis, 

The Google Nest Learning Thermostat G4, measures the indoor humidity and uses the outdoor humidity from internet weather data.  If you have a Humidifier or Dehumidifier attached you can set the desired indoor humidity.  When in heating mode you should have a humidifier and keep the humidity inside around 40%.  A gas furnace tends to dry out the air which leads to lower enthalpy and static electricity problems. 
In the summer months the Air Conditioner can condense the moister in the home.  In the south where the humidity is very high, the Google Nest Learning Thermostat can run the air conditioner a little longer to remove more of the indoor humidity.  Additionally in the coastal areas the blower fans operate at lower speed to allow the air to remaining in contact with the coil longer thus removing more moisture. 

AC Cooling Wizard

[Nexusis]

Yes thank you for the info but the issue is that the  RH data on the thermostat doesn’t change or update based on the outdoor temperature as advertised in the app. Outdoor temps are hovering around -15C, where indoor humidity should be set around 30% but the G4 doesn’t update as it should. If you set it to 40% manually, it stays like that and doesn’t change?

[SteveInMD]

I have a Nest ver 4 thermostat setup to work with the humidifier. I can adjust the humidity level in the Home app. It works while in heating mode. I have it connected to the * terminal. I have two questions….

1) I can control the thermostat in the Home app but I can’t get it to show up in the Nest app. Is this normal? Or is something not right?

2) Can the humidifier be set to run when the hvac system is running the heat? The thermostat would need to turn on both the humidifier and also the air handler fan. I set up my mother’s Nest thermostat to do this and it works fine but it’s an older version. I don’t see how to do this with ver 4.

[Elderpine]

For 1), this is normal - the Gen 4 nest only works with google home.  It doesn’t work with the Nest app unfortunately.

For 2), I remember seeing that setting when adding the humidifier, but I can’t find it now.  Others may know where to find it after setup, or maybe go through the setup again?

[Mrjoeski]

While you may be correct that an external (bypass) or internal humidifier can be set up and controlled by the Gen 4 thermostat, upon initial setup, there is a programming error/omisssion that does not allow the end user to access the System Configuration settings, as was available in the Gen 3. 

This is a glaring omission on Googles part, despite the help menu directing you to the System Configuration tab, it simply is not present. Without this link, you cannot manipulate the humidifier setting after initial setup. For example: If humidity is needed, I want the water solenoid valve to only open when heat is active AND the fan is on. As it stands now, only upon initial setup, can I tell the system to run the fan or not, when humidity is required to be added, BUT there is no way way to set that to happen ONLY when heat is commanded on. Instead, the blower will activate, at any time humidity is demanded, heating or not. With a bypass humidifier, this is an inefficient way of increasing humidity, as cool air is now being passed through the humidifier media vs hot air which picks up more moisture as it passes through the media. The Gen 3 thermostat had all of these configuration settings available and my system worked fantastic with it. I purchased the Gen 4 for the system’s supposed ability to adjust humidity demand based upon outside temperature vs Gen 3 needing the user to lower the humidity  as outdoor temps drop. Until Google fixes this glaring issue, I’d avoid the Gen 4 thermostat. 

[tolandis1]

New to humidifiers.  I have a music room with antique devices.  Pianos, Violanos, etc., here in Las Vegas humidity is running around 20 according to my 4th gen. google nests.  Need to get it to over 30.  Thinking about getting installed a steam humidifier for at least one of the a/c furnace combinations.  I have three, larger house.  After all the posts it does seem like the nest can operate the humidifier as needed separate from the rest of the system?  Am I correct?  I don't want to know too much these systems as I can allow a knowledgeable installer do this.  Main question I see Aprilaire mentioned is that the only brand or any other brands compatible with Nest?  Is there a steam humidifier, nest 4th generation compatibility list?  If needed?  Thanks to all Todd, tolandis@yahoo

Hope I can find this thread again.  Feel free to email me, thanks

[SteveInMD]

After an update about two or three weeks ago, there are now more options for controlling a humidifier...

• Enable or disable
• Adjust the humidity set point
• Set quiet hours (when the humidifier won't run) 

And under Advanced Configuration...

• Select Stand alone or Heat integrated mode
• Select Active the fan or Don't activate the fan

All is right again with humidity control. I have an AprilAire humidifier connected to my hvac system. I set my to 'Standalone' and 'Activate fan'. It now humidifies even when the heat is not running. (I know some will  say it's not supposed to work that way. I have no interest is that debate. It works quite well for me.) The thermostat will control a steam injection system or a traditional water panel system. A Nest Pro installer is not needed. The settings are available to all.

[tolandis1]

Which Aprilaire model do you use, if hard to get to not a big issue.  Thanks

[SteveInMD]

I have the 700 model. Water panel with an integrated fan. At my last house I had the 800 (I think) which steam injection. Either way the thermostat sends 24 volts to it when calling for humidity. The steam version also needs line voltage.