11-16-2021 08:18 AM - edited 11-16-2021 09:39 AM
Just bought a new Nest Learning 3rd generation thermostat and will be hooking it up soon. I have a single stage American Standard heat pump and a 2 stage American Standard natural gas furnace. I have looked and can not find an answer on if this will work and a wiring diagram. Right now the current thermostat turns on the heat pump if the outside temperature is > 35 and if the outside temperature is below 35 the compressor turns off and the gas furnace stage one fires up and after a while (timer?) the furnace turns on stage two. I want to make sure the heat pump and the gas furnace are not on at the same time.
11-16-2021 12:51 PM
Eddie- it handles all those things very well automatically. It locks out the heat pump and makes its own determination about when to fire up both additional stages.
you’ll find it makes a dynamic decision about locking out the first stage based on actual conditions outside and inside , and often will opt to keep the heat pump on a little longer despite the lower effective throughput. Have an open mind.
12-16-2021 06:40 AM - edited 12-16-2021 06:43 AM
It handles dual fuel, but not very well. As near as I can tell it does not look at how much you turned the thermostat up, just how cold it is outside. An example after being away for a few days the temperature in my house had dropped to 50F. It was a warm day outside so I decided to warm the house up and stay there that night. At about 11:30 AM I used the app to set the thermostat to 70F, so a 20 degree rise. Most thermostats turn on AUX heat if the temperature rise is more than a few degrees. This one did not. It ran the heatpump all day. When I went to bed at 10:30 PM the heatpump had only warmed the house to 69. Heatpumps are designed more to keep a house warm (mine does) than to heat a house up. Several people have post on the community with the same problem. Everything works as it should when the outside temperature is below 30F, so it's not a wiring or heating system error, it's just poor programming or the programmers not knowing how a dual fuel system works.
01-03-2022 02:11 PM
I returned mine to Home Depot. If you happen on this thread looking for Dual Fuel information be sure to check out the person who replies to you. The person that replied to my question only ever answered one question, mine. These thermostats physically work with Dual Fuel but the programming does not have the proper logic to effectively heat with dual fuel