10-11-2022 01:14 PM
We are replacing our furnace with a new 2-stage model (York TM8Y). We previously had a single-stage furnace. We also have a single-stage A/C unit.
It looks like the thermostat wire to the Nest is only 5 conductors. Based on the diagrams I have seen, it looks like I would need 6 conductors to accomplish this:
My Nest Backplate (v5.3) is currently wired up with 1-5 above. I noticed in the Nest Pro Installer Guide that it says:
Fan relay (G) is optional. However, without a G wire, Nest will not be able to control the fan independent of heating.
Common wire (C) not required in most cases, but strongly recommended.
Does this mean I could use the Common wire (C) conductor to add my W2 for my 2nd stage of heating?
I would rather not use the Fan relay (G) as sometimes I like to turn the fan on to circulate air. We have a tri-level and the temperature from the top to the bottom can be several degrees different.
How can I tell if I can use the Common wire?
Answered! Go to the Recommended Answer.
10-15-2022 10:35 AM
Hi folks,
@Patrick_Caezza, thanks for the help!
@MrRyan, thanks for reaching out. Since you have a Nest Learning Thermostat, you could put your stage 2 heating on the W2 terminal. Also, if you're not experiencing any issues with your system without the C wire, that means that your system is fine with how your Nest Thermostat charges its batteries using your cooling and heating wires.
Thanks,
Edward
10-11-2022 11:29 PM
Post a picture of the original thermostat's wiring
10-12-2022 09:58 AM
I don't have it. I have had the Nest 3rd gen installed for about 6 years. The issue is we are replacing a single-stage furnace with a 2-stage furnace. I am looking for guidance on how to wire it.
10-15-2022 10:35 AM
Hi folks,
@Patrick_Caezza, thanks for the help!
@MrRyan, thanks for reaching out. Since you have a Nest Learning Thermostat, you could put your stage 2 heating on the W2 terminal. Also, if you're not experiencing any issues with your system without the C wire, that means that your system is fine with how your Nest Thermostat charges its batteries using your cooling and heating wires.
Thanks,
Edward
10-18-2022 10:39 AM
Hi MrRyan,
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
10-18-2022 10:59 AM
I haven't tried re-purposing the C wire for my 2nd stage heating, but I understand that is my option. I wasn't sure if there is some kind of analog-to-digital interface conversion kit that could make it so my thermostat has all functions available, regardless of how many wires, and translates it at the furnace into however many wires are needed.
My HVAC contractor has suggested I don't tell Nest that I have a 2-stage heater and instead set the furnace so that the 2nd stage comes on after 20 minutes.
10-19-2022 09:33 AM
Hi MrRyan,
Thanks for the response. I'm not sure of an analog-to-digital interface converter either but please observe your Nest Thermostat for now and let us know if anything comes up.
Thanks,
Edward
10-24-2022 03:22 PM
Hi MrRyan,
I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.
Thanks,
Edward