Do I Need a C Wire for Humidifier Control with Nest 4th gen?

[NBrammann]

We’re replacing our Sensi thermostat with a Nest Learning Thermostat (4th gen) and want it to control our existing 24V whole-home humidifier (currently controlled by a manual humidistat). Our HVAC company confirmed compatibility but mentioned that adding a C wire would add cost if it’s needed.

We don’t currently have a C wire connected. Given that we’ll be using the Nest to control both the HVAC system and the humidifier, is a dedicated C wire required for reliable performance—or will Power Sharing be sufficient?

Appreciate any guidance from the community!

[EduardoN]

Hi @NBrammann, 

Thank you very much for contacting this community! I understand that you're replacing your Sensi Thermostat with a Nest Learning Thermostat (4th gen), but your home has a 24V humidifier and you were told that you need to add a C wire through your HVAC company. Don't worry, I'm here to help you!

Regarding your question about whether a C wire is necessary, it is highly recommended that you use this wire so that your system's performance is as appropriate and reliable as possible, even though the installation may incur an additional cost.

Please feel free to share any additional details you think might be relevant.

Best regards,
Eduardo