Nest learning thermostat compatibility with variable compressor heat pump

[Kaybee3]

Hi all,

My Learning Thermostat has been working for years with no problems controlling a basic, builder-original single-stage cooling/single-stage gas heating HVAC.  But now it's time to replace the HVAC - hopefully not the thermostat - and I have a proposal from our local tech.

They're proposing to install:

• a 2-3 ton variable speed (compressor, not fan) GE heat pump (GAUH2436ZGDA)
• a 2-stage dual fuel Trane furnace/air handler (S8X2A040M3PTAA)
• a Bosch BCC100 wifi thermostat
• various additional miscellanea

I'm intending to push back on the furnace, based on a relatively mild local climate and aversion to avoidable combustion of fossil fuels.  But my real question is about the heat pump with its variable compressor and the potentially gratuitous thermostat replacement.

I know the Nest thermostat can handle 2-stage cooling, but a variable compressor (not the air handler fan... the heat pump compressor) sounds like it wouldn't be compatible with that.  Or at least, not without losing all of the efficiency perks of the variable compressor.

But GE's documentation somewhat nebulously (to my inexperienced mind, at least) indicates that this particular series is specifically designed for compatibility with "older", "basic" 24V thermostats, and even more nebulously seems to imply that the heat pump unit makes its own decisions about controlling the compressor.  That seems to suggest that the thermostat might only need to view it as a 1-stage cooling device, without needing to know that the compressor is actually variable?  (I imagine this might be based on inlet vapor pressure or some such?)

Any knowledgeable thoughts on whether the Nest thermostat would be able to correctly control this potentially self-modulating(??) variable compressor heat pump?  (I can't emphasize enough that this is not a question about variable fan speed in the air handler... that's a different subject, unrelated to this question.)

Thanks in advance for any assistance!

[Patrick_Caezza · Accepted solution]

@Kaybee3 

From what I have learned about these three items, the Nest Learning Thermostat, 3rd Gen, will work fine with them.

There is nothing that I read that tells me the heat pump would work with the Nest. Both the heat pump and air handler use the 24V control setup.

Disclaimer: This is my personal opinion based on my experience. I make no guarantee that this will work.

[Kaybee3]

@Patrick_Caezza - Thank you for the helpful reply.  Just to clarify, because I might be misunderstanding, is the "would" on the second line supposed to be "wouldn't"?  I apologize for the confusion on my end, but the first line seems to suggest that setup probably would work while the second seems to indicate there's no evidence that it would work.  (Which... could both be true, I guess.  🙂)

Again, thank you for your help!

[Patrick_Caezza]

@Kaybee3 

Sorry about that.

You are correct, and it should read wouldn't.

Basically, your system will work with a Nest thermostat.

[Kaybee3]

No worries, and thank you again for the assistance. 🙂

[zoeuvre]

Hi Kaybee3, 
 

I’m glad that everything has been sorted out. 
 

As we got our resolution here, I'm going to mark this thread as complete. I'll be locking this thread if we won't hear back from you again in 24 hours. Should that happen, feel free to create a new one if you have more questions or have other concerns in the future. 
 

Thanks for your help, @Patrick_Caezza, Mark, and Jake. 

All the best,

Zoe

[Jake]

Hey Kaybee3,

Thanks for the help Patrick_Caezza.

I wanted to check in and see if you managed to see Patrick_Caezza's post. Please let me know if you have any questions from here. I would be happy to assist, and make sure you are good to go.

Best regards,
Jake

[Markjosephp]

Hello there,

Thanks for your assistance here, Jake.

@Kaybee3 I'm checking back in — how's it going? Still need our help?

Regards,

Mark