Learn about multistage heating and cooling system

Multistage heating and cooling systems help households use less energy. All Google Nest Thermostats support multiple stages of heating and cooling, but exactly how many varies between different thermostat models.

Support for multistage heating and cooling varies between Nest thermostat models:

  • The Nest Thermostat E supports one stage of heating, one stage of cooling, and a second stage of either heating or cooling. You’ll need to manually set the Star connector icon / OB connector as your second stage in the Equipment menu. If you need help, contact a Nest Pro.
  • The 2nd and 3rd generation Nest Learning Thermostats support up to three stages of heating and two stages of cooling for conventional systems, and two stages of heating and cooling with auxiliary heat for heat pumps.
  • 1st generation Nest Learning Thermostats support two stages of heating and one stage of cooling for conventional systems, and heat pumps with auxiliary heat.

To learn more about Nest thermostat support for different types of systems, please see: Nest thermostat technical specifications.

How multistage systems work

Single stage systems can’t fine tune the temperature of the air they circulate through your home. Many older systems are single-stage, on-or-off systems with only one level of heating or cooling. Modern single stage systems are often found in small homes and places where the weather is typically mild, while multistage systems are typically needed to heat large homes or meet the demands of very cold or hot weather.

Multistage systems work like a ceiling fan with different speeds: low, medium, and high. Instead of simply switching on heating or cooling, they can adjust the temperature of the air pushed through your home’s vents to reach the temperature you set as efficiently or as quickly as possible.

They’re more efficient than single stage systems because they can use the lowest level of heating or cooling needed or can use higher levels on very cold or hot days. Using lower stages of heating or cooling is more efficient because the system doesn’t need to turn on and off as often to maintain a constant temperature. Higher stages also use more energy, so running lower stages for longer to reach your desired temperature can save energy.

How Nest thermostats manage different stages of heating and cooling

Nest thermostats use their Time to Temperature algorithms to estimate how long it will take to warm or cool your home to a specific temperature. If your system has more than one stage of heating or cooling, this estimate helps your thermostat know when to turn on different stages to reach the target temperature efficiently and on time.

If your system’s first stage of heating or cooling won’t reach your desired temperature in a reasonable amount of time, your Nest thermostat will turn on additional stages of heating or cooling to ensure that you’re kept comfortable.

How Nest thermostats manage different stage of heating and cooling

Nest thermostats use their Time to Temperature algorithms to estimate how long it will take to warm or cool your home to a specific temperature. If your system has more than one stage of heating or cooling, this estimate helps your thermostat know when to turn on different stages to reach the target temperature efficiently and on time.

If your system’s first stage of heating or cooling won’t reach your desired temperature in a reasonable amount of time, your Nest thermostat will turn on additional stages of heating or cooling to ensure that you’re kept comfortable.

Multiple stage are handled differently right after thermostat installation

Multiple stages of heating and cooling are handled a bit differently for a short period after your Nest thermostat has been installed. This is because your thermostat needs time to learn and customize energy saving and comfort features like Time-to-Temperature to your home. In most homes, Time-to-Temperature will take about a week to learn, but could take more if your heating or cooling system isn’t used frequently.

So your thermostat will handle multiple stages of heating or cooling differently while it learns about your home, your temperature preferences, and your system’s efficiency. Before your Nest thermostat has activated Time-to-Temperature, the second stage of heating or cooling will turn on when you adjust the set point 3.3°F beyond the current temperature, while the third stage will need a change of at least 7°F to activate. 

Fan speed control for multiple stage of heating or cooling

Multistage systems typically only have one fan speed while single stage systems sometimes have multiple fan speeds.
  • 1st, 2nd and 3rd generation Nest Learning Thermostats can support systems with either multiple fan speeds or with multiple stages of heating and/or cooling.

  • Nest Thermostat E does not support multiple fan speeds.

If you need help determining whether your system has one fan speed or multiple fan speeds, consult your system’s manual or contact a Nest Pro.

How to tell if you have a multistage system

Most multistage systems can be recognized by the wires attached to the thermostat. Single stage systems will only have one wire for heating (in the W or W1 connector) and one wire for cooling (in the Y or Y1 connector). Single stage heat pumps only have Y1 for both heating and cooling.

Multistage systems will have more than one heating or cooling wire. For example, systems with three stage conventional heat will have wires in the W1, W2, and W3 connectors. Systems with two stage cooling or a heat pump will have wires in the Y1 and Y2 connectors. Some heat pumps also have auxiliary heat, an additional stage of heating that is typically used when the heat pump compressor can’t keep up with cold weather conditions. This wire is usually found in the W2/AUX connector on your thermostat.

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