Help with Nest Thermostat Wiring

[Newnesthelp]

Hello! We are upgrading from an old Honeywell mercury two-wire (R + W) system to a Nest Thermostat and need help with the wiring. We have a simple demand on/off heat system with no ac or blower units. We need to power four Nest Thermostats, so we have pulled additional necessary wires and are hoping to use a universal step down transformer providing 24-volt power to all four devices via the new wires. We now have the original heating system R and W wires along with 2 new wires coming from the step down transformer (C and R). We are assuming that the C wire from the transformer can be directly connected to the C terminal of the thermostat. Our question is what to do with the R wire coming from the transformer, assuming the R terminal on the thermostat is already occupied by the original R wire from the heating system. Any help greatly appreciated!

[RenzJ]

Hi Newnesthelp,

Thanks for posting here in the Google Nest Community. We'd be happy to take a look into this for you. What we can recommend for a dual transformer setup like yours is that since there is a separate transformer for heating and cooling, our Nest Learning Thermostat is ideal for this setup as it has RC and RH thermal. You can connect the R wire to the RC for the cooling system and to the RH for your heating system.

Here’s the Nest Learning Thermostat for you to check before making the purchase.

Let us know if that helps.

Best,

Renz 

[Newnesthelp]

Thanks so much for your reply. We had an electrician come o who helped us figure out that part of the reason we weren’t able to get power was that the original installers had switched the R and W wires, so even with the Nest Power Connector wouldn’t work and we just couldn’t figure that out. Got it all working without using the transformer.

[RenzJ]

Hello Newnesthelp,

Thanks for the update. Glad to hear that everything is sorted out. If you have other questions or concerns, you know where to find us.

Cheers,

Renz