Understanding Fan Control

Mysa Smart Thermostat gives you several ways to control how and when your system's fan runs. Depending on how your HVAC system is wired and configured, your thermostat may control the fan directly—or your HVAC system may handle fan operation automatically.

Thermostat Fan Control vs. System Fan Control

Your Mysa's wiring and configuration code determines who controls the fan—your HVAC system or the thermostat.

System-Controlled Fan

If you do not have a G-wire (typically configuration codes ending in A):

Your HVAC system controls the fan automatically
The fan runs only when heating or cooling is required
You will not see separate fan settings in the app or on the thermostat

Thermostat-Controlled Fan

If you do have a G-wire (typically configuration codes ending in B for conventional systems, or J, L, N, P for heat pumps):

Mysa directly controls the fan using the G-wire
You will see fan options such as Fan Only Mode in the app and on the thermostat
Additional features like Minimum Fan Runtime become available

Tip Not sure of your configuration code? Find it in the Mysa app under Device Settings > Thermostat Configuration.

Fan Only Mode

Available for: Thermostat-controlled fan systems (G-wire required)

Fan Only Mode runs the HVAC fan continuously without heating or cooling. This helps circulate air for better airflow, comfort, and filtration.

How Fan Only Mode Works

When selected, the fan turns on immediately and runs continuously
No heating or cooling will run while in this mode
Turn it off by selecting another mode (Heat, Cool, Auto, Aux/Emergency, Off)
If your system does not have a G-wire, Fan Only Mode will not appear

How to Use Fan Only Mode

In the Mysa app:

Tap the device tile
Tap the Mode selection menu
Select Fan Only

On the thermostat:

Wake the display
Tap the right arrow to change mode
Select Fan Only

Minimum Fan Runtime

Available for: Thermostat-controlled fan systems (G-wire required)

Minimum Fan Runtime lets you choose a set amount of time each hour to run your fan—even when your system is not heating or cooling.

Available Settings

0 minutes (default) — Fan runs only during heating/cooling
15 minutes per hour
30 minutes per hour
45 minutes per hour
60 minutes per hour — Fan runs continuously

How It Works

If you choose 30 minutes per hour:

If the fan runs for 10 minutes while heating or cooling, Mysa will run it an additional 20 minutes within the same hour
Mysa divides the hour into periods so extra fan time is spread appropriately based on your heating/cooling needs
Fan runtime is added only if needed to meet your minimum selection
Fan runtime triggers even when the thermostat is in Off mode

How to Set Minimum Fan Runtime

Tap the device tile in the Mysa app
Tap Settings > Thermostat Configuration
Scroll to Minimum Fan Runtime Per Hour and select your preference

Benefits of Fan Control

Improved air quality — Continuous circulation helps filter and distribute air more evenly, reducing dust, allergens, and pollutants
Enhanced comfort — Keeps air moving to prevent hot or cold spots, ensuring more consistent temperatures across rooms
Energy efficiency — Maintains a more stable temperature, reducing the need for frequent heating or cooling cycles
Humidity control — Helps manage humidity levels by preventing moisture buildup