Nest thermostat C wire

[Peter666]

Before buying the nest thermostat it didn't specify that I needed a C wire.  I have a two wire system.  White and Red.

No HVAC, heat only.  Now I'm getting a C wire needed.  Really regretting buying the nest.  Thinking about throwing it in the garbage and putting the old one back.  

Question:  Do I or do I not need an additional C WIRE?

[sporfrog]

Hi,

Sorry your particular system is not working without a C wire. Just to verify, were the two wires connected to R and W on the old thermostat?

The need for a C (common) wire is dependant on many things, most of which is the particular HVAC system.  There are so many different brands, models, ages of systems it is hard to know for sure if it is needed.  Most "smart" or electronic thermostats require a power source of some kind and many smart thermostats require a c wire.

Don't throw it away just yet.  Here are some options to consider:

1. If there is a free wire not used connect it to C or Common at both the HVAC unit and the Nest thermostat. By the sounds of it this in not an option for you, but worth exploring.
2. If there are no free unused wires, consider the Nest Power Connector. It works best if there is a C wiring terminal at the HVAC unit. However a transformer can be added if necessary.
3. In some cases running a new thermostat cable with a few extras wires so that one can be used as C (common) is also an option.

[Patrick_Caezza]

Did you use the compatibility checker here?

https://store.google.com/us/widget/compatibility/thermostat

It clearly states that you need the C wire or the Nest Power Connector if you are using the Google Nest Thermostat.

There is a good chance you'll also need an external 24VAC transformer.

 

[MelbaDT]

Hey folks, 

Thanks for the detailed response and for providing the wiring diagram, Patrick_Caezza and sporfrog. 

Peter666, sorry if you feel that way. We recommend that you check on our online Compatibility Checker so that you will know your system’s compatibility before purchasing any of our Nest thermostats. Rest assured that we'll also take your experience as feedback so we can deliver a better experience in the future. 

Best, 

Melba

[MelbaDT]

Hi, 

I haven't heard from you in a while so I'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the community.
 

Best, 

Melba