Learning t-stat refuses to use aux heat to reach scheduled setpoint within a reasonable time

[Tom_R_Cincy]

I have a Nest Learning Thermostat (NLT) wired to a Trane heat pump and air handler with strip heaters using Y1, G, O, W2, C, * and RH connections.  The NLT heating schedule is set to 64 at 11:00 PM and 68 at 7:00 AM daily.  With outside temperatures now in the 20’s and 30’s, it has been taking until 8 or even 9 in the AM for the house to warm to 68 unless I manually change the setpoint up a degree and then back to 68 - which immediately turns on aux heat.

I started with Early-On set to 1 hour, but turned it off after reading posts that suggested aux heat would not come on when using Early-On.  Now it is taking even longer to reach 68 for the same outside temperature.  Aux heat eventually comes on, but not until as late as 8:35.  I would really like the NLT to work like my programmable Trane t-stat, which would start the heat pump and, if necessary, the strip heaters early enough to have the house at 68 by ~7:00 AM.

The rest of my heating-related settings:  Home/Away Off, Auto-Schedule Off, Time-to-Temp Ready, Heat Pump Balance Max comfort.  I don’t understand why the NLT will not use aux heat for a long time after missing the scheduled setpoint when I have it set to Max Comfort.  I would appreciate any help to change my settings to deliver 68 within a short time after 7:00 AM.

[Markjosephp]

Hello Tom_R_Cincy,

Thank you for reaching out and providing detailed information about your Nest Learning Thermostat (NLT) setup and the challenges you're facing with achieving your desired temperature in the morning. We understand your concerns regarding the delay in reaching the desired temperature of 68°F, especially during colder outside temperatures. Your description of the issue, the attempts you've made with Early-On settings, and the desired functionality similar to your previous thermostat are clear and informative.

Let's try adjusting a few settings to optimize your Nest Thermostat's performance:

• Early-On Feature.
  • While you've turned it off, Early-On can be beneficial for pre-heating your home. Turn it back on, and set it for at least 30 minutes before your desired temperature. This should prompt the system to start heating in advance.
• Heat Pump Balance.
  • You have it set to "Max Comfort," which is good. This setting allows the Nest to prioritize comfort over efficiency, potentially using auxiliary heat to reach the set temperature faster.
• Temperature Buffer.
  • In your schedule settings, try setting the temperature a degree or two higher than your desired comfort temperature. This might encourage the Nest to start heating a bit earlier.

Remember, the ideal thermostat settings can vary based on the specifics of your home and heating system, so some experimentation may be needed to find the perfect configuration for your comfort.

I hope this helps, and stay warm!

Regards,
Mark

[Tom_R_Cincy]

Thanks Mark,

I turned on early-on again with a 1 hour preheat duration.  Because we had guests, I also changed the scheduled overnight temperature to 68 and the 7:00 AM setpoint to 72.  The outdoor temperature was 39 and at 7:15, the house was still at 68 and at 8:00, the house was only up to 69 when the aux heat finally came on.  At 9:00, the house was up to 71, but still short of the 72 setpoint.

How can I configure this thermostat to use aux heat sooner?  It is not logical that an hour of preheat and another hour without aux heat (yielding only 1 degree warmer and still 3 degrees from the setpoint) would be required before the NLT would turn on the aux heat!

It is hard for me to believe that this is the way the Nest is programmed.

Please help me if there is a settings change that will allow the aux heat to come on without having to wait 2 hours in the cold.

Tom

[Markjosephp]

Hi there,

You can adjust the settings on your Nest Thermostat to optimize the performance of the auxiliary heat. Here's a step-by-step guide:

1. Open the Nest app on your smartphone or tablet.
2. Select the thermostat you want to adjust.
3. Tap on "Settings".
4. Choose "Equipment" to access your heating system settings.
5. Select "Heat Pump Balance" or a similar option.
6. Adjust the balance between auxiliary heat and regular heat.
   1. You may want to increase the use of auxiliary heat to achieve your desired temperature more quickly.
7. Save your changes and monitor the thermostat's performance.
8. Restart the thermostat to make it reflect.

If you have any more questions, feel free to ask.

Warm regards,
Mark

[Tom_R_Cincy]

Mark,

The only heat pump balance setting available to me is already set to Max Comfort.  There is nothing available under Equipment.  I believe the program logic is faulty and unfortunately, will need to find a better-designed thermostat.

Tom

[Markjosephp]

Hi Tome,

I'm sorry for the late reply. If the Heat Pump Balance doesn’t appear in the app or on your thermostat, you might have an incompatible system, or there could be a wiring issue that makes your thermostat think you have an incompatible system. Could you share with us a photo of your thermostat's wiring?

I'll look forward to your response.

Best,
Mark

[Tom_R_Cincy]

Thanks Mark,

Heat Pump Balance is set to Max Comfort.  My wiring has been checked by my HVAC company (I will try to find a way to send you a photo).

However, this is the problem - the NLT's logic is still taking over an hour before turning on aux heat - even when the temperature is 5 degrees below the setpoint.

Tom

[Tom_R_Cincy]

 

[Markjosephp]

Hey Tom,

I appreciate the information you provided. It appears to be more about system efficiency. Since we have checked your thermostat's settings to ensure that all parameters related to auxiliary heat and temperature differentials are configured correctly, have you had a chance to contact an HVAC company? They may be able to provide additional insights or adjustments to improve the system's performance.

Let us know how it goes.

Best,
Mark

[Tom_R_Cincy]

Mark,

It is definitely not an issue of system efficiency.  I can get the aux heat to turn on and heat the house in a short time by manually adjusting the setpoint up and back down one degree.

The problem is that the NLT will not turn on aux heat for over 1 hour after the schedule changes the setpoint from 64 to 68.  The program tries to raise the temperature with only the heat pump for 1-2 hours.

I need help from someone on the Google Nest team who will either help me with a corrective setting change or will put in a change request to fix the bug in the logic of the schedule section of the code.

Tom