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how to configure Nest thermostat for two stages of heating

lennie08
Community Member

Hi. I just recently installed a Nest thermostat with wiring terminals R,C,W,Y,G and *OB. Also installed is a new two stage heating furnace with single stage cooling. How do I configure thermostat to work with two stage heating when I don't have a W2 terminal? 

For the record, I'm an HVAC technician.

 

18 REPLIES 18

Ryan_G
Community Specialist
Community Specialist

Hi lennie08,

 

Thanks for reaching out and we're sorry for the delay.

 

For a two stage heating heat pump, there should be a Y1 and Y2 wire available. Could you check the HVAC main board and take a photo of the wire connected to it.

 

I hope to hear from you soon.

 

Regards,

Ryan

EEEO
Community Member

I recently also bought a Nest thermostat--to be clear, it's NOT the learning thermostat, so it has 6 total terminal connections on the baseplate--R, G, C, Y, W, and */OB.

I installed a new Goodman two-stage furnace. The previous thermostat did not support two-stage heating, thus the upgrade to the Nest. All wires were hooked up as they were on the old thermostat, with an additional wire for W2(2nd stage heat) on the furnace control board connected to the */OB terminal on the Nest. After wiring and going through the setup on my phone, the thermostat turns on the AC when calling for heat. Obviously this isn't what we want! It appears the thermostat thinks there is a heat pump installed. After a 55 minute call to the Nest help line, I was told that the thermostat is compatible with 2 stage furnaces, but apparently not mine. At this point, I'm dubious that this thermostat is actually compatible with 2 stage furnaces. There doesn't appear to be a way to configure the */OB terminal for 2nd stage heat, though the support person I talked to says there is, he couldn't tell me how to do it. 

 

If you're looking for a thermostat that supports a two stage furnace, I'd avoid this thermostat and go with one that has actual W1 and W2 terminals. At this point I'm so disgusted that I'm going to return it and go with a different brand altogether. Since I can't get the hours I've wasted messing with this back, at least I'll get my money back.

Ryan_G also needs to read more carefully. The OP never said he had a heat pump, he said he had a furnace. This might be why the OP didn't bother replying to you.

For the record, I'm not an HVAC tech,  but I've been a building contractor for 25 years and have installed multiple furnaces, unit heaters, and central air conditioners. I called my buddy who is an HVAC tech, and he was stumped as well.

Ryan_G
Community Specialist
Community Specialist

Hi EEEO,

 

Thanks for sharing your thoughts here in the Google Nest Community.

 

We're doing our best to answer and provide assistance to every community member. I know that this is the main goal here and I'd like to thank you for helping us out here.

 

@lennie08, I'd like to check if you've already installed your thermostat to your HVAC system. Let us know how it goes by replying to this thread.

 

Best regards,

Ryan

airking
Community Member

why are there no clear instructions available to connect two stage cooling i am assuming its to be connected to * ob but i can't find that anywhere

DaveBC
Community Member

I'm trying to make my mind about buying the Nest Thermostat for a 2 Stages heating furnace (No cooling/no heatpump).  There is contradictions and ambiguity about the 2 Stages heating support of the Nest (not the learning model).  This tread could have nailed it but this is yet not answering the question from the OP.

So is the Nest Thermostat supports 2 Stages Heating with the Star Connector?

splinke
Community Member

I have the same question. Does the Nest Thermostat support 2-stage heating furnaces?

Jhonleanmel
Community Specialist
Community Specialist

Hi splinke,

 

Thanks for posting. The Nest Learning Thermostat does support two stages of heating.

 

Best,

Mel

Where does the W2 wire go?

Jhonleanmel
Community Specialist
Community Specialist

Hi splinke,

 

Could you share a photo of your current thermostat's wiring? Also the Nest Learning Thermostat has a W2 terminal for that wire.

 

Best,

Mel

We do not have air conditioning but have a two-stage furnace. There are only four wires going to the thermostat: Red (main power), Green (fan), W1 (heating stage 1), and W2 (heating stage 2). There is no fifth wire available for an independent C (common) attachment.

Although the specs for the non-learning Nest (the one I am interested in) claim it can handle two-stage heating, that unit lacks the W2 terminal that the learning version has. So, I am assuming the non-learning version does not properly handle two-stage heating.

I can leave the W2 wire disconnected, and the furnace will still function fine--always at the stage 1 level. But I will be unable to exploit the stage 2 heating, unless another terminal on the non-learning Nest can substitute for the W2 terminal. It has been very difficult figuring all of this out, and it is very unclear how the non-learning Nest handles multi-stage heating/cooling--that information seems purposefully hidden.

Even if two-stage heating is somehow possible with the non-learning Nest, I have the additional problem of the lack of a C wire, which is apparently important to power these WiFi smart thermostats. It seems that the G (fan) wire could be substituted, but then I would not be able to run the fan without heat. I understand that the Nest can try to use the power when heating is on to recharge and/or cycle furnace power when necessary, but it sounds like this approach is a bit sketchy and can actually wear out the furnace.

At this point, I am thinking that the best option is to stick with a dumb (battery powered) thermostat that is specifically designed with a W2 terminal.

Jhonleanmel
Community Specialist
Community Specialist

Hi splinke,

 

Thanks for clarifying that. You're right, the Nest Thermostat does not have the W2 wire terminal, which means it cannot accommodate two stages of heating. You can contact a Nest Pro technician to discuss your options for rewiring your system to work with your Nest Thermostat.

Best,

Mel

Hello there,

 

Thanks for helping, Mel.

 

@splinke, I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.

Regards,

Mark

Hello splinke,

 

I'm checking in to make sure that you've seen our response. If you have any further questions or concerns, please let us know before we lock this thread in 24 hours.

 

Regards,

Mark

splinke
Community Member

Yes, I saw the post about the Nest not being able to handle two-stage heating. I will be getting a non-smart thermostat to be able to do that. Thanks.

Markjosephp
Community Specialist
Community Specialist

Hi splinke,

 

Thanks for getting back to us. I've got some more information for you about Nest system compatibility that might help. Please take a look at this article and let us know if you have more questions.

 

Regards,

Mark

Thanks Mark,  the new factsheet nailed it:  

 

Heating and Cooling: 1 stage of heating (W1) and cooling (Y1) and a second stage of either heating (W2) or cooling (Y2).

 

So, I have a Two stage Furnace, I  wired the W2 to the *O/B connector and it works fine.  When you setup the Nest for the first time, it does allow you to assign the *O/B port to W2 second stage.

splinke
Community Member

That is useful information. It is too bad that there is no way to know that until you have already purchased a unit, and it does not seem possible based on the labeling on the hardware. I already bought a non-smart thermostat that is working well for two-stage heating.

Markjosephp
Community Specialist
Community Specialist

Hello there,

 

Sounds great! @DaveBC, I'm glad you've found the answer you were looking for, and I appreciate you letting us know how you configured your thermostat.

 

@splinke, Thanks for posting on this thread. We understand your thoughts, but you can always check out our resources at the Google Nest Help Center page. If you ever change your mind, we'll be here to help.

 

Please let us know if you have any further questions; otherwise, we'll close the thread in 24 hours

 

Thanks,

Mark