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How does a Nest 3rd gen measure humidity?

ShawnDoe
Community Member

‎03-07-2025 06:16 PM

I recently changed all of my HVAC equipment including my whole-house humidifier. I now have an AprilAire 800. My experience with the new system is different than the old system. One thing is that Nest keeps the humidifier on even though the target % is met. I don't remember the old system doing that. Which made me wonder, how does Nest gauge humidity? Is there a humidistat in it? Most answers on the web say no. So how does it do it? 

My Nest controls the humidifier via the * wire. I have the fan set to on always as it is variable speed and I also have a whole-house air filter.  That's not an issue. In the Nest settings, under Options, under Humidifier, I have the setting to On. The Quiet Time is off. The target % is 45. But often Nest is now keeping the humidity on past the target by 5 points but sometimes as much as 10. Is there a reason changing my humidifier would make Nest seemingly start going over the target setting.

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kcruzgonzalez
Community Specialist
Community Specialist

‎03-10-2025 09:15 PM

Hello ShawnDoe,

Thanks for reaching out to the Nest Community. We're happy to help you with your Nest Thermostat 3rd Gen and your new AprilAire 800 humidifier.

I understand you're seeing discrepancies between your target humidity and the actual humidity levels, which is certainly puzzling after a major HVAC system change.

Given the significant changes to your HVAC system, I strongly recommend contacting a qualified HVAC technician specializing in Nest Thermostats and AprilAire humidifiers. They'll be best equipped to diagnose and resolve any potential conflicts between these systems.

Here's how you can find qualified technicians in your area:

  • For installation or installation issues: Contact our installation partner, OnTech.

  • For Troubleshooting: Contact a qualified technical professional (Nest Pro). To find a Nest Pro:

    • Go to Google.com in your web browser.

    • Search for "Nest Pro HVAC technician near [Your ZIP code]."

Please note that the cost of the service call will be your responsibility, so it's important to choose a qualified professional experienced with Nest products. Also, please do not expect the Nest Pro to troubleshoot any issue over the phone; they will need to come to your home.

Please let me know if you have any further questions.

 

Best regards,

Kevin

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