Connecting Humidifier to Nest 3rd Gen

[Rodeng]

I have an older drum style humidifier with rotating foam pad.  This is powered from a separate 24V transformer than my furnace so in essence I have two wires near the Nest thermostat that I want to use specifically in the Nest for completing the circuit that turns the humidifier on and off.  Can the Nest handle another power supply say connected to the R ie power from the furnace's transformer and from the Humidifier transformer and the second humidifier wire connector connected to the * terminal?  I hope this is clear.

I do not want to power the humidifier from the furnace directly as I do not know if it can handle that load.

As a side note, the furnace has an independent humidifier relay module on/off that closes when the furnace calls for heat.  

[Rodeng]

Replying to my own post.  I am checking to see what load the low voltage thermostat strip in the furnace can take.  Possibly it will handle the small drum motor.  Anyone have any experience?

[luciaaa]

Hi, @Rodeng!

Thank you for contacting the community. I understand you have an older drum-style humidifier with its own dedicated 24V transformer, separate from your furnace's transformer. You'd like to use two wires from the humidifier's circuit to control it through your Nest thermostat, specifically connecting one wire to the Nest's "R" (power) terminal and the other to the "*" (star) terminal. I'm happy to assist you with your concern.

To provide the most accurate guidance, please answer the following questions:

• Do you have a conventional or heat pump system?
• Conventional System: Typically consists of two pieces of equipment (furnace and AC).
• Heat Pump: Handles both heating and cooling with a single unit.
• What is the Nest thermostat model you would like to install? 

Additionally, please provide:

• A clear photograph of your current thermostat's wiring configuration.
• A clear photograph of the wiring diagram for your humidifier.

This information will allow me to determine the compatibility of your system with your desired Nest thermostat model.

Also, it is crucial that a qualified HVAC technician perform the humidifier installation. Improper installation, including incorrect wiring or software configuration, can lead to abnormal HVAC operation and potential system damage.

Please keep me updated.

Best regards, 

Ana

[Rodeng]

Thank you for replying. I have a Nest Gen 3 A0013 on a conventional gas furnace. I have decided to scrap the idea of connecting the old humidifier transformer to the Nest.  The two sources of power into the Nest will likely cause problems if not electrical shorts and damage.  Instead my second idea is described in the attached diagrams.  Powering the humidifier off of the * from the Nest as shown in the wiring diagrams.  The drum motor is the only electrical draw - no valve solenoid.  Typical motor is 3W @ 24V AC.  

Unfortunately I receive an error message -  I do not have permission to upload images. 

[luciaaa]

Hi, @Rodeng!

Thank you for your prompt response. To address the error message you're receiving after connecting the humidifier's drum motor to the Nest's * terminal, I strongly recommend contacting a Nest Pro or qualified HVAC technician. Improper installation can lead to HVAC system malfunctions and potential damage. They can ensure proper wiring and confirm compatibility with your Nest Learning Thermostat 3rd Gen.

Please keep me updated.

Best regards, 

Ana

[Rodeng]

Sorry, it was not clear, the error message was that I do not have permission to upload pictures.  How can I fix this?

Regards

Ralph

[luciaaa]

Hi, @Rodeng!

Thank you for getting back to me. I'm sorry to hear you can't upload pictures here. No problem! You can easily create a folder in Google Drive and upload the pictures there. Refer to the following articles from the Google Drive Help for instructions: Upload files & folders to Google Drive. After that, please share the link with "anyone with the link" access: 

• Select the file you want to share.

• Select Share.

• Under General access, select the down arrow.

• Choose Anyone with the link.

• To decide what role people will have, select Viewer, Commenter, or Editor.

• Select Copy link.

• Select Done.

• Paste the link in the place you want to share it.

That way, I'll be able to see the images and give you better support: 

Please keep updated.

Best regards, 

Ana

[Rodeng]

In a nutshell, previous thermostat had two separate terminals just for the humidifier.  One option with the nest is a separate humidistat but the Nest can control humidity.  Therefore, I would like to use the Nest, run power from the * terminal to the drum humidifier, from the humidifier to the C terminal on the furnace.  I show these wiring diagrams and a view of what type of humidifier I have.  The drum motors are typically 3W.  Will this work?  Is there enough power to run the drum motor this way?  See https://drive.google.com/drive/folders/17YQxQwhTQcD16mMrFkzIXDNxKDHJX5mU?usp=sharing

[luciaaa]

Hi, @Rodeng!

Thanks for getting back to me and for the picture link. I've taken a look, and it seems like your best option is to have an HVAC technician check it out. Since this installation is pretty technical, I can't give you specific wiring instructions for the thermostat. I wouldn't want to risk any inconveniences or damage to your HVAC system. A technician can tell you if you can safely run power from the * terminal to the drum humidifier, and then from the humidifier to the C terminal on your furnace. They'll also make sure everything is compatible and get it installed properly.

Feel free to reply if you have any questions.

Best regards, 

Ana