How does a thermostat control two stages of heating?

For this sequence the thermostat must be configured for two (2) stages of heating.

Note: When a thermostat is configured for (2) stages of heating, (W) enables the first stage of heating and (W2) enables the second stage of heating.

1. At the beginning of the heating cycle the thermostat will start the supply fan.
2. If the thermostat has high heating demand (the room temperature is 1.1°F or more below its thermostats heat set point), it will start its first stage of heating and then, one minute later, it will start its second stage of heating.
3. Both stages of heating will remain active until the room’s temperature drops to 1°F below its thermostats heat set point, at which point the thermostat will then turn Off the second stage of heating and keep the first stage of heating enabled until the room reaches its heat set-point.
4. If the room’s temperature drops back to 1.1°F or more below its heat set point, while the first stage of heating is running, the thermostat will re-enable the second stage of heating and use both the first and second stages of heating to bring the room to its heat set-point.
5. Once the room is at its heat set point, the heating cycle will end. The fan will remain enabled for 1 minute after the heating cycle to purge any extra heat out of the HVAC unit and into the room.

Click here for information on Anticipation Degrees.
Click here for information on Purge Cycles.

At the beginning of the heating cycle the thermostat will start the supply fan.
If the thermostat has low heating demand (the room temperature is 1°F or less below the thermostats heat set point), it will start its first stage of heating and give the first stage the opportunity to provide all the necessary heating to condition the room.
The first stage of heating will remain active until the room reaches its thermostats heat set-point.
If while the first stage of heating is active, the room’s temperature goes 1.1°F or more below the thermostat’s heat set point, the thermostat will start the second stage of heating and used both the first and second stages to bring the room to its heat set-point.
Once the room is at its heat set point, the heating cycle will end. The fan will remain enabled for 1 minute after the heating cycle to purge any extra heat out of the HVAC unit and into the room.

Click here for information on Anticipation Degrees.
Click here for information on Purge Cycles.

This staging sequence accomplishes two goals:

It quickly heats the room in high heating demand situations, and then relaxes the number of stages to provide a more comfortable supply temperature and heating rate when the room is just being maintained.
It allows for the greatest efficiency value to comfort ratio.

On the thermostat’s history graph you will see the following:

The dark blue line shows the room temperature.
The light red horizontal line shows the thermostats heat set-point.
A light red shaded area indicates the thermostat has started a heating cycle.
If one stage of heat is/are active, there will be a single grey bar at the bottom of the red shaded area.
If two stages of heat is/are active, there will be two grey bars (one stacked on top of the other) at the bottom of the red shaded area.