Nest Learning Thermostat - Wiring Compatibility

[steviey_bc]

Hi, i was wondering if anyone could give me direction on the electrical swap over from my current thermostat which is a Venstar T8850 to a Google Nest Learning Thermostat recently purchased before I'd have to reach out to a proressional..

Currently the wires on my Venstar are as follows:

White - W3/AUX

W2 - Open

Orange - W1/OB

Y2 - Open

Yellow - Y1

Green - G

Red - R

Black - C 

White & Black to 2 "Sensor" labelled ports

On my Google Nest Learning Thermostat I have ports for Y1, Y2, G, OB, Rc, W1, W2AUX, C, *, Rh 

So the questions are in differences are:

Does White go to W2 AUX?

Does Orange go to W1 or OB?

Does Red go to Rc or Rh?

and where do the White/Black wires that are currently on the "Sensor" go?

For the rest I am just assuming they go to their counterpart labelled. Yellow Y1-Y1, Green G-G, Black C-C

Thank you for your time.

[alejandom]

Hi @steviey_bc,

You're on the right track! While I can't provide specific electrical advice due to safety concerns, I can help you map your Venstar T8850 wiring to your Google Nest Learning Thermostat based on the information you provided. Here's a possible translation:

Venstar to Nest Learning Thermostat:

• Yellow (Y1): Connects to Y1 on Nest
• Green (G): Connects to G on Nest
• Red (R): Connects to Rh on Nest (Important Note: See below for Rc)
• Black (C): Connects to C on Nest
• White (W3/AUX): Do not connect to Nest (W3/Aux on Venstar likely controls auxiliary heat, not supported by most Nest thermostats)
• Orange (W1/OB): Possible connection to OB on Nest (Important Note: See below for OB)
• White/Black ("Sensor" wires): Cannot be directly connected to Nest (These wires likely connect to an external sensor, not supported by the Nest thermostat itself)

Important Notes:

• Rc vs Rh: Both Rc and Rh provide power to the Nest thermostat. In most cases, you'll use Rh. Rc is typically only used for specific boiler systems. Consult your Nest Learning Thermostat manual or online resources to confirm if Rc is required for your system.

• OB vs W1: The orange wire (W1/OB) on your Venstar could be for either heat pump operation (OB) or secondary heat (W1). Here's how to determine which:

  • Heat Pump System: If you have a heat pump system, connect the orange wire to the OB terminal on your Nest thermostat.
  • Secondary Heat System: If you have a furnace or boiler as your secondary heat source (in addition to a heat pump), connect the orange wire to the W1 terminal on your Nest thermostat.

Double-Checking and Safety:

• Double-check your wiring: Before making any connections, refer to the Nest Learning Thermostat installation guide for your specific model. Ensure the wire colors from your Venstar match the compatible terminals on your Nest.
• Consult a professional (optional): If you're unsure about any aspect of the wiring or installation process, consider consulting a qualified HVAC technician. They can ensure your Nest thermostat is wired correctly and functions safely with your existing HVAC system.

Here are some additional resources that might be helpful:

• Nest Learning Thermostat Installation Guide: https://support.google.com/googlenest/answer/9274936?hl=en
• Nest Thermostat Compatibility: https://support.google.com/googlenest/answer/9246656?hl=en

Regards, 

Mario. 

[steviey_bc]

Thank you for the very informative reply Mario! Greatly appreciated! - Steve