Replacing my existing thermostat with google nest thermostat

[Shohag072]

Hi,

I need to replace my existing honeywell thermostat with nest learning thermostat. My existing thermostat has 4 wires - W,C,R,K. But the new nest thermostat doesn't have K. How should I proceed? I can provide a picture of my existing thermostat if needed. 

Thanks in advance.

Regards

[Markjosephp · Accepted solution]

Hello Shohag072,
 

I'm glad to hear that you're looking to upgrade to a Nest Learning Thermostat. The absence of the K (usually for a black wire) might not be an issue, as Nest Thermostats are designed to work without it in most cases. The K wire is often used for cooling systems that require a constant 24V power supply.

Before proceeding, it's essential to ensure compatibility. You can check the Nest Thermostat Compatibility checker online. If you're unsure, providing a picture of your existing thermostat could indeed be helpful for a more accurate assessment.

In many installations, the W, C, and R wires are the primary ones for heating systems. The Nest Thermostat typically requires a common wire (C) for power, and if your system lacks it, you might need to use a Nest Power Connector.

Let me know if you have more questions.

Best regards,
Mark

[Shohag072]

Hi Mark,

Thanks for your reply. Here is the picture of my existing thermostat wiring. It would be great if you can recommend where should I connect the K wire. I understand the C will be connected to C, W will be connected to W1, R will be connected to Rh. The only confusion is the K wire. I've also attached the new google learning thermostat's back panel picture. Thanks in advance. 

[Markjosephp]

Hi there,

Thanks for the additional details. To be sure, can you tell me the make and model of your HVAC system? What kind of heating system do you have? Also, could you provide us with your system voltage? You can usually find it on your system's label.

Keep me posted.

Warm regards,
Mark

[Shohag072]

Hi Mark,

My furnace is Lenox EL296UHV Elite series (gas furnace) and AC is Lenox Merit Series 13ACX Unit. Both are very latest & updated equipment and are installed in 2022. However, I couldn't locate the system voltage in my system's label.

Thanks again

Kazi

[Markjosephp]

Hi Kazi,

Is your system high-voltage? High-voltage thermostats are often built into the wall and typically have 2-4 thick wires coming out of the thermostat. Your system might be between 110 and 240 VAC. But in some cases, it is possible to make a high-voltage system Nest-compatible. Contact a local professional and have them install a step-down transformer to 20–30 V.

Let me know if you have more questions.

Thanks,
Mark

[Shohag072]

Hi Mark,

My system is not high voltage for sure. I just need to know where should I terminate the K wire.

Thanks,

Kazi

[Markjosephp]

Hey there,

Thanks for clarifying. Can you check your system's control board and confirm how the wires from your thermostat are being labeled? You can share a photo of it so we can also check its placement.

I'll look forward to your response.

Best,
Mark