Nest Thermostat - Gen 3 - WaterFurnace Geothermal Aux Heat control

[SBurns]

I have a question about temporarily disabling Aux Heat usage on my Nest 3Gen Thermostat. I have it setup and working well with a WaterFurnace geothermal heating system. It uses Stage 1, Stage 2 and Aux efficiently and I have no problems during normal operation.

Recently I have acquired a trailer mounted generator that has enough capacity to power the Compressor Stage of my furnace but not the Aux Heat portion. How during a power outage, when using my generator, can I definitively disable Aux Heat? I have to ensure it will not come on as the huge draw will be detrimental to the generator.

Do I simply use the Nest app and visit:

A) Heat Pump Balance - Heat Pump Balance - Off

B) Heat Pump Balance - Choose max duration = 0

C) A) + B)

D) Remove the Aux wire while on generator

E) Go into the setup on the thermostat itself and map out Aux Heat as not being available on my furnace?

My goal is to ensure Aux Heat will never be turned on while using my generator setup.

Pictures of thermostat configuration below.

Thank you in advance

Scott

[Houptee]

You cant have any of the balance options on or Nest will try to decide when to kick on Aux heat.

If you set it to OFF then you pick a lockout temp it will kick on Aux when outside temp is below the lockout temp.

So you could set a really low lockout temp whenever you use the generator. Like 0 deg F so it wont try to use Aux unless it is colder outside than 0 deg.

But if you dont want to manually change the Nest every time you could wire a switch in the W2 wire like a regular wall switch for a light and just turn off the switch when you are on generator power breaking the W2 circuit to prevent it from kicking on the Aux heat.

[SBurns]

Thank you. So simply removing the Aux/W2 wire (or the switch idea) without any thermostat reprogramming is a valid option? The Nest won't become confused that my furnace has Aux capabilities in the Nest programming but without the wire connected it will operate as if I do not?

[Houptee]

Now that you mentioned it, I am not sure how the Nest is going to react to the switch method. It might report "wiring changes detected" every time you turned off the w2 wire.

So the other solution is shut off the breaker for the auxiliary heat killing the main power circuit when on generator power. 

[SBurns]

Yes that is where my complexity comes into play. The 60A breaker is just for the compressor stage. The 100A is for the Aux and the basic controls for the furnace. I need the 100A on to run the controls but not allow the Aux to come on.

[Houptee]

Do you have an air handler with the heating coils kit installed?

I think the breakers for the heat coils inside the air handler only cut power to the coils but keep the air handler powered up from the main breaker feed coming from the breaker panel but not 100% sure. You could try shutting them off inside the air handler and see if the air handler main board and blower stays powered on.

[SBurns]

The Water Furnace is a complete unit with the compressor, aux heater grid and blower all in one unit so I am not sure if there are breakers inside just for the aux heater. The only external component is the circulation pumps for moving the fluid through the underground loop.

[EdwardT]

Hi folks,

@Houptee, thanks for the help!

@SBurns, thanks for reaching out. If you don't have a separate breaker for the AUX heat, the only option that we have is to remove the wire. I understand that this is not ideal since you have to reconfigure it when you connect the wire. Our team is always looking for ways to improve and we'll take this as feedback.

Thanks,

Edward

[SBurns]

So as I understand it my options are:

1) Currently I have the system setup for Heat Pump Balance - Balanced, Max Duration 1 Hour.

Is it true I can set Heat Pump Balance - Off and then under Equipment - Aux Heat Lockout option will be enabled. At that point as long as I set the temperature here to be lower than the outside temp Aux Heat should not be called upon? I would only do this in the event of going onto generator during a power outage.

2) Switch in the Aux wire

 - What will the Nest do if the switch is off? It will still call Heat Stage 1 and 2 and the Aux will just not turn on? Will the thermostat complain about the missing wire? Is there any programming needed or will this just work?

Thanks

Scott...

[EdwardT]

Hi SBurns,

Thanks for the response. You're correct but If it gets colder outside than the set lockout temperature, your heat pump will use AUX heat.

If you turn off the breakers for the Aux wire, the Nest Thermostat would still detect that there's a wire connected to the W2 terminal. However, you might get an error code since it's going to detect that there's no power in it.

Thanks,

Edward

[Jhonleanmel]

Hi folks,

Chiming in to see if you still need assistance with this. Let us know if you have additional questions ― we'd love to help.

Best,
Mel

[Jhonleanmel]

Hi everyone,

Just one quick final check in here since activity has slowed down. We haven't heard from you in a while so we'll be locking this thread if there is no update after 24 hours. If you have any new questions, updates or just a discussion topic, feel free to start a new thread in the Community.

Thanks,
Mel