topic Re: Dual fuel wiring 2-stage gas furnace and single stage heat pump in Nest Thermostats

Dual fuel wiring 2-stage gas furnace and single stage heat pump

Tab1962 — Fri, 01 Aug 2025 22:26:59 GMT

I have an Amana two stage gas furnace with a single stage Amana heat pump currently controlled by Honeywell stat with EIM. I like to replace with the Nest 4th gen (I think). I have no aux heating like electric strips or whatever. Currently uses a balance point of 35F and above (outside temp sensor) this the heat pump provides heat, below this the gas furnace provides heat. These never run at same time. There is also a setting for "emergency heat" that even though the temp is above 35F when this is enabled, only the gas furnace provides heat. Emergency heat would be used when some issue with heat pump and the heat pump and gas furnace never run at the same time. I'd like to understand the wiring diagram for stat, furnace control, and heat pump control. I also want to confirm that the Nest supports the same balance point and "emergency heat" setup I have now. I'd love to send you some pics in this post, but does not seem to allow me. Thanks, Tracy

Re: Dual fuel wiring 2-stage gas furnace and single stage heat pump

Derickf — Wed, 06 Aug 2025 05:40:26 GMT

Hi @Tab1962,

Thanks for reaching out. I understand you're looking to replace your current thermostat with a Nest Learning Thermostat (4th Gen), and you have questions about the wiring, balance point, and emergency heat functions. I appreciated you providing a detailed description of your setup. I'm happy to assist.

To give you the most accurate wiring guidance, I'll need to see how your existing thermostat is wired.

Could you please share a picture of your current wiring, or did you receive an error message when you tried to attach it?
- You can attach the photo using the camera icon. If you receive an error when trying to attach it, please let me know.

I'll be waiting for your reply.

Best regards,

Derick.

Re: Dual fuel wiring 2-stage gas furnace and single stage heat pump

Tab1962 — Wed, 06 Aug 2025 11:26:02 GMT

Thanks for the reply Derick, but I don’t have any camera icon shown. I have the first ones like bold, italic, etc but don’t have the last several including the camera. Thx. Tracy.

Re: Dual fuel wiring 2-stage gas furnace and single stage heat pump

Tab1962 — Wed, 06 Aug 2025 11:29:36 GMT

I think I figured out how to enable the camera. See the pics attached.
Furnace control

Re: Dual fuel wiring 2-stage gas furnace and single stage heat pump

Tab1962 — Wed, 06 Aug 2025 11:31:04 GMT

Now I get an error about exceeding size when I try to post any other pics. Ugg. Tracy.

Re: Dual fuel wiring 2-stage gas furnace and single stage heat pump

Derickf — Thu, 07 Aug 2025 05:46:03 GMT

Hi there!

Thanks for your reply and providing the wiring picture of your current setup. After checking the wiring in our compatibility checker tool, I can see that your current setup is compatible with the Nest Learning Thermostat (3rd and 4th Gen).

Answering your question about the balance point and auxiliary heat:

The Nest Learning Thermostat can be configured to manage a dual-fuel system with a balance point and an emergency heat function just like your current setup.

You can find more information in the following article: Heat Pump Balance.

If you have any other questions, let me know.

Best regards,

Derick.

Re: Dual fuel wiring 2-stage gas furnace and single stage heat pump

Tab1962 — Thu, 07 Aug 2025 08:21:10 GMT

OK Derick thanks.