Go Control TBZ48 - Aux heat setting is this for dual fuel?

Currently using TBZ48 (two of them, 2 systems) for controlling a single stage heat/cool, I am upgrading soon to two stage heat/cool with heatpump and furnace (dual fuel). In the user guide I see reference to an Aux heat setting will this work to switch from Heatpump over to furnace (fossil fuel changeover) that is shutting off heatpump (Y1/Y2) and signaling W1/W2? Can't seem to find any info about this scenario in the user guide so I am thinking probably does not work like this. Something else you would recommend for dual fuel changeover?

I think this is more of a question for your installer. My understanding is that heat pumps stop working efficiently below a certain temp. And I think that depends on what you have installed and what its rated for. I think that can also be damaged by running them at extremely low temps. So the aux heating is typically a backup heating method. It could be electric elements, or propane, or oil, etc. So the change over temp I believe is the critical question, which I think would be best answered by your installer.

Thanks for the reply! The installer can tell me what the stat needs to do to control the system but is not as familiar with capabilities of the stat (especially not Go Control). I should add that my use case is a bit different than the typical changeover requirement to optimize for heat pump until it becomes too cold outside. I want to prioritize for furnace and only run heat pump when its more energy efficient to do so. Here in Southern Calif that is pretty much never right now, gas is still less costly than electric, but if/when gas prices increase, or I install solar, or the cost of energy at off-peak times makes it economical to run heat pump. So I need to have more flexible control of the Aux heat directly, given outside temp, energy cost rules, etc. Given more I have read about Aux heat on other thermostats (like Ecobee), I think the Go Control may do what I am looking for, using rules to tell it when to switch from regular heat to Aux heat. What I won't get though is two stage heat/fan control in Aux heat, since there is only one contact for Aux heat. Seems what I would need is a 4H/2C stat like the Ecobee premium, Honeywell Prestige, etc. the Go Control is a 3H/2C.

Thanks for the clarification. Yes, that's an interesting use case. One confusing term in your post is "changeover." In the heat pump world, changeover is the value that reverses the flow of the refrigerant to switch from heating to cooling. I think you are referring to changeover here from the perspective of changing from gas heat to heat pump heat.

It sounds like you do have a 3H/2C system. I looked at the TBZ48 manual and it looks like it fits your use case. It has two stage heat and cool and an aux mode that can be enabled in the setting of the thermostat. The only problem is that the manual doesn't address how to wire for 2 stage heat with aux. It looks like page 3 of the manual is how you want to wire it. But I don't know where the aux wire is.....

One way to figure it out, would be to open up your HVAC unit (turn off the breaker first). And see if you can trace the wire bundle from the thermostat to the control board. Most of the control boards are labeled with W1, W2, Y1, Y2, C, O, etc. I have two HVAC units, both have single stage heat/cool with aux heat. I had to trace out the wires from the control board to ensure I wiring it correctly.

If you can't figure it out, you might need to confirm with Go Control, which wire is energized when aux mode is enabled and you have 2 stage heat.

Ah, I see why that was confusing now, yes I mean "changeover" from primary heat to Aux heat. For my scenario Aux will just end up being used most if not all the time. I looked at my options in Hubitat for the device, and it has ability to control "emergency heat" which should activate W1/heat stage 1 (also referred to Aux in manual). The critical thing is that the heat pump must be shut off when W1 is activated, so I will reach out to Go Control and confirm if it works like this. I suppose I could also pull stat off wall and bench test, which I may do anyway to be certain, but will see what Go Control says first. Ultimately, I will need to upgrade to a 4H/2C stat, to get full 2 stage Aux heat control, but would still like to confirm if CG will work until then.

Page 19 of the manual confirms that Emergency Heat mode turns on the aux heating and does not turn on the compressor.

Indeed, I see it now page 19. Thank you! RTFM issue :roll_eyes: Good I can start with GC and try that out with a habitat rule to set "emergency heat" based on outdoor temp, time of day, etc. I can't test this yet since I don't have a heat pump yet the new system is not yet installed but did want to make sure I understood control options to decide if or when I may need new 4H/2C stat. Liking what I am reading/hearing about Bosch HP that it is variable speed and modulates based on its own algorithm and suction temp/pressure, so I do not need a proprietary communicating thermostat. Will update after install if I end up sticking with GC stat and can keep it in Aux heat via hubitat. I will still need a 4H to get 2 stage heat, but where I live may not really need it.

Hi from Reddit! Not stalking, just browsing new, lol

Hello! My install is tentatively mid Jan so I'll be back with an update around then. Played a bit with rules that would let me enable emergency/aux heat using my current stats and while its doable in the rule, not sure what best trigger it. Maybe look for any change to "heat" then immediately switch to emergency. Its a nice challenge, but I read up some more on ecobee 3 lite and it would sure be more intuitive. Glad to learn it can handle 2 stage aux heat. I will probably go that route, and I can get $75 rebate to help offset the $150 cost.

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