Nest Support

Questions about Nest Learning Thermostat or Nest Protect: Smoke + CO alarm? We've got answers, videos, and plenty of resources to help you out.

Is the Nest Learning Thermostat compatible with dual fuel hybrid heating and cooling systems?

A dual fuel heating and cooling system (also called a hybrid or packaged system) is a combination of a heat pump for primary heating and cooling and a furnace (usually gas or oil) that provides a second and/or third stage of heating. The Nest Learning Thermostat is compatible with these systems and supports up to 2 alternate heat sources.

What is a dual fuel system?

A dual fuel system is the combination of a heat pump with a full-sized furnace (usually gas or oil). This type of system will use the heat pump to heat your home when the weather is mild, but still cold. This is more efficient than burning gas or oil.

But when it gets very cold--usually around 35ºF/2ºC--the heat pump shuts down and the furnace alone heats your home. While heat pumps can heat at these lower temperatures, they aren’t as effective in the cold weather. In dual fuel systems, the heat pump and the furnace must not run at the same time in order to protect each system.

How are dual fuel systems different from a heat pump with auxiliary heat?

Heat pumps with auxiliary heat (usually electric strip heat) also combine a heat pump with an additional heat source for cold weather situations. The difference is that the additional heat is part of the heat pump instead of a separate system, and will run in tandem with it.

How can I tell which one I have?

To find out if you have a dual fuel system, you will need to check if you have a furnace and a heat pump that are part of the same system. This means that both the furnace and the heat pump will be controlled by the same thermostat and is likely a dual fuel system.

Here are some clues:

  • If you have both a furnace and a heat pump in your home and only one thermostat, you probably have a dual fuel system. If you have both a furnace and a heat pump in your home with multiple thermostats, you still may have a dual fuel system.
  • Take the cover off of the thermostat and look at the wires. If you see a wire in the O, B, or O/B connector and a wire in W1, you likely have a dual fuel system (however, sometimes the wire for auxiliary strip heat is also in the W1 connector, so this is not a sure test).

Use the Nest Thermostat Compatibility tool or contact a local Nest Certified Professional to learn more.

How do I set up my Nest Thermostat with a dual fuel system?

While setting up your Nest Thermostat, choosing the incorrect options for a dual fuel system can result in damage to your system, so it’s important for a professional to assess the requirements for your specific dual fuel configuration.

A professional installer can choose the right settings for each type of system in Pro Setup that can be accessed in the EQUIPMENT section of SETTINGS.

If you have a dual fuel system, you can contact a local Nest Certified Professional to install and setup your Nest Thermostat.

Once the installation is complete, you should ask your installer what options they selected for your system so you’ll have them handy if you ever need to re-enter them yourself.