Dual fuel and rapid heat up after adjusting thermostat up

[papa_K]

I have a dual fuel system (heat pump & gas furnace) connected to my Nest thermostat.  The furnace starts as it should when the outside temperature is below my threshold (40 deg F).  However, when substantially adjusting the thermostat up (ex. 10 deg F), the furnace does not come on to rapidly heat up as it did before with our Trane thermostat.  Below is the way I have it wired and the setup that is programmed.  I'm not sure if it's clear in the photos, but it's a black wire connected to the W1 terminal (same on Trane thermostat) and a brown wire connected to the * terminal.  The brown wire was connected to the X2 terminal on our old Trane thermostat.  Is there a way for the Nest thermostat to have the furnace start when the outside temperature is cold (<40 deg F) AND also when adjusting the thermostat up substantially?  I'm at a loss and have tried everything I know to do.  Thanks in advance.

[Jenelyn_O]

Hi papa_K,

Thanks for posting in Google Nest Community Forum.

If you have a dual fuel system, you can set a lockout temperature manually in the Nest thermostat's Equipment menu. Please share the photo of your old wiring for us to double check its wiring configuration.

I'll look forward to your response. 

Also, you can check this out for additional information.

Best,

Jenelyn

[papa_K]

Thanks, Jenelyn.   I think by the lockout temperature you are referring to the temperature below which the heat pump switches over to the backup heat (in our case a gas furnace).  That feature is working fine, and when the outside temperature is below 40 deg F, the system uses the gas furnace for heat.  What is not working like our old thermostat is when we increase the temperature by a large amount while above the lockout temperature, the system will only use the heat pump to raise temperature even though it may take many hours to get to the new setting.  Our olf thermostat would use the backup heat if the temperature was adjusted up by more than 5 deg F of the current inside temperature.  Below is a photo of our old thermostat wiring.  It' an Amercian Standard (Trane).

[Jenelyn_O]

Hi papa_K,

Thanks for the follow-up information and for being specific on what your concern is. Glad that the feature I'm talking about is working just fine. Could you please share the make and model of your HVAC system? it would help us to move forward.  

Best,

Jenelyn

[papa_K]

Hi Jenelyn.

Below is the information from my condenser unit outside and the air handler unit inside.  The furnace is part of the air handler assembly and is an American Standard Freedom 80 Comfort-R.

Thanks again.

Keith

 

[Jenelyn_O]

Hi papa_K,

Thanks for the follow up information! Upon checking, your system is compatible with Nest Learning Thermostat.

If you adjust your Max Comfort, your Nest thermostat will try to get your home to the temperature you want. Have you tried adjusting it? If not yet, I suggest moving the black wire from W1 going to the W2 terminal before adjusting your Max Comfort since it's the original terminal for alt heat. Make sure to turn the breaker off before touching the wires. 

Best,

Jenelyn

[papa_K]

Thanks again, Jenelyn.  I assume when you are talking about "Max Comfort" you are referring to the heat pump balance adjustment that is available on regular heat pump systems.  When your system is dual fuel, the heat pump balance adjustment does not even show on the thermostat menu.

We had the thermostat in eco mode while we were away recently and the inside temperature got down to the mid-fifties, while the outside temperature was above the lockout of 40 deg F.  When we began our return home, we adjusted our thermostat with our phone app to 70 deg F.  When we arrived home about four hours later, the inside temperature had only increased to the mid-sixties.  What we would like it to do is use the backup heat (gas furnace) until the inside temperature gets within 5 deg F of the setting (or some reasonable temp band).  I am not having any luck in discovering how to get it to do that and I'm beginning to think that the Nest just isn't capable.  Seems like a simple software update could fix this.

[Jenelyn_O]

Hey papa_K,

Thanks for that information. Back up heat would only turn on when the Nest Thermostat detects that your outdoor temperature is below your lock out temperature. In your case, the reason why the thermostat only uses your heat pump is because your outdoor condition is beyond your lock out temperature. 

I suggest adjusting your lockout temperature depending on what outdoor condition you currently have. Your Google Nest thermostat can use Wi-Fi to check the outdoor climate near your home. When the weather outside gets colder than your lockout temperature, your thermostat will use your backup heat. For example: If you have 40 degrees outdoor temperature make sure that your lockout temperature is set to 40 degrees above. 

Regards,

Jenelyn

[papa_K]

Jenelyn,

Thanks for your attempts to help.  It appears that the Nest is not as capable as our old American Standard (Trane) thermostat, which had a lockout temperature AND would use backup heat for large increases in the thermostat setting.  Seems like Nest would fix that with a software update.  All the necessary information to be able to program it that way is available in the thermostat.  Thanks again!

[Jenelyn_O]

Hi papa_K,

I appreciate your insights about it. We’re always looking for ways to improve and we’ll take this as feedback. Please let me know if you have any questions or concerns otherwise, I'll be locking this thread after 24 hours.

Best,

Jenelyn