Replacing Honeywell EIM with Google Nest Learning Thermostat

[MoisesPio]

I have a Honeywell Thermostat that is connected to what they call "Equipment Interface Module (or EIM)" in the basement, and I want to replace it with the Nest Learning Thermostat (4th gen).

Google confirmed that Nest Thermostat should be compatible with my system, but I still have an unanswered question:

The thermostat controller is only using 2 out of the 16 wires that are connected to the EIM. Does this mean I would have to wire all the 16 wires to upstairs so I can connect them to Nest? In other words, I want to bypass the EIM without losing any of the functionalities and controls I currently have.

Thanks!

[catheryn]

Hi @MoisesPio,

Thanks for posting in the community.

I understand you're having questions about wiring when replacing your Honeywell EIM with a Nest thermostat. Let me help you with that!

Before we proceed, I'd like to gather some additional information to provide the best guidance:

• What type of system do you have? (e.g., gas furnace, heat pump)
• Which Nest Thermostat are you planning to use?

In the meantime, you might find the Compatibility Checker helpful for quick and easy instructions.

Please let me know how it goes, and we'll work together to ensure a successful replacement.

Thank you, 

Catheryn

[MoisesPio]

@catheryn -- it's a gas furnace/HRV system. Looking to replace my current thermostat with a 4th-gen Nest.

[catheryn]

Hi @MoisesPio, 

Thanks for your reply and the additional information. 

To ensure compatibility, please provide a clear photo of the control board, including any labels or markings on the connected cables

Thanks in advance,

Catheryn. 

[MoisesPio]

The photos of both the hub and the controller are linked in my original post.

The labels of the connected wires in the control panel, from top to bottom are: R C W W2 Y G U2 U2 RH R C S2 S2 S1 S1

[catheryn]

Hi @MoisesPio,

Thanks for your reply. 

Since your current system has this type of wiring, we can't guarantee that the existing cables will be suitable for the Nest Thermostat. There can be a voltage difference that could impact its performance

To ensure a successful installation and its optimal functionality, we recommend contacting a Nest Pro technician. They can assess your specific setup and provide expert advice on the best solution on this matter. 

On the following links, you can find useful information about technicians: 

Professional installation and service 

Nest Pro installation website (On tech)

Let me know how this goes and if you need more assistance. 

Thank you, 

Catheryn.