topic Re: C Wire Requirements in Nest Thermostats

C Wire Requirements

timr1 — Fri, 28 Oct 2022 14:30:28 GMT

Hello everyone -

Can anyone explain why my new Nest Thermostat requires a 'C' Wire, but the older Nest Learning Thermostat does not require this? They are both connected to the same heating system for radiant floor heating ONLY.

Thank you,

Re: C Wire Requirements

EdwardT — Wed, 02 Nov 2022 02:31:17 GMT

Hi timr1,

Thanks for reaching out. The new Nest Thermostat requires a C wire for a Heat only system for a stable power source. You can click on this link to learn more about key differences between Nest thermostats and what systems will work with each.

Thanks,

Edward

Re: C Wire Requirements

EdwardT — Sat, 05 Nov 2022 02:54:07 GMT

Hi timr1,

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do.

Thanks,

Edward

Re: C Wire Requirements

timr1 — Sat, 05 Nov 2022 12:59:57 GMT

Hi Edward -

Thank you, the link was helpful and I have now purchased and installed and external adaptor in addition to the Nest Power Connector.

However, it didn't really explain the differences between the Nest Learning Thermostat and the Nest Thermostat that makes this requirement necessary. To my human eye - the items seem virtually identical in terms of their functions - so why does the Nest require the external power source (or 'C' wire')? It just seems a little weird... :).

Re: C Wire Requirements

Markjosephp — Sat, 05 Nov 2022 14:33:02 GMT

Hi folks,

I wanted to stop by and see how I could help.

Thanks for the assistance, @EdwardT.

@timr1, I've got some more information for you. The Nest Thermostat (model 2020) often requires a C wire to work, though there are cases where it might not be needed. This is most likely because it was engineered to identify when a system needed more power to reliably power the thermostat. Unlike the Nest Learning Thermostat, it can charge its built-in battery using the heating and cooling wires.

Here are some references to help you install your new Nest Power Connector on your HVAC system.

Feel free to let us know if you have more questions in mind.

Best regards,

Mark

Re: C Wire Requirements

Markjosephp — Tue, 08 Nov 2022 17:08:19 GMT

Hi timr1,

I hope you've got the answer you're looking for. If you're still in need of any assistance, feel free to let us know.

Best regards,

Mark

Re: C Wire Requirements

Markjosephp — Wed, 09 Nov 2022 18:46:50 GMT

Hello timr1,

I want to check if you have seen my response posted above. Let us know if you have additional questions; otherwise, we'll be locking the thread within 24 hours.

Best regards,

Mark