Understanding Fan Control

Last updated: August 4, 2026

Mysa Smart Thermostat gives you several ways to control how and when your HVAC 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 may see fan options such as Fan Only, fan runtime settings, and fan speed settings, depending on your HVAC configuration

  • Unsupported fan options are hidden automatically

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, such as Heat, Cool, Auto, Aux/Emergency, or 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:

  1. Tap the device tile

  2. Tap the Mode selection menu

  3. Select Fan Only

On the thermostat:

  1. Wake the display

  2. Tap the right arrow to change mode

  3. Select FAN

Fan Settings: On, Auto, Runtime

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

Mysa's fan runtime settings let you decide whether the fan runs only during heating or cooling calls, continuously, or for a minimum amount of time each hour.

On vs. Auto

  • On — The fan runs continuously, while heating or cooling still turns on as needed.

  • Auto — The fan runs only when heating or cooling is active.

Minimum Fan Runtime Per Hour

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, or even if set to Off mode.

Available Runtime Settings

  • 15 minutes per hour

  • 30 minutes per hour

  • 45 minutes per hour

How Fan Runtime 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 can still run when the thermostat is in Off mode

How to Set Fan Control

  1. Tap the device tile in the Mysa app

  2. On the device control screen, tap the Fan Control icon on the right side of the screen

  3. In Fan Control, choose one of the following:

    • On — Fan runs continuously for improved air circulation; heating and/or cooling will engage as required

    • Auto — Fan only runs during a heating or cooling call

    • Runtime — Fan runs for a minimum amount of time each hour

  4. If you choose Runtime, select 15 min, 30 min, or 45 min under Min Runtime Per Hour

  5. Tap Done

Fan Speeds

Some HVAC systems support multiple fan speeds. If your system is configured for multi-speed fan control, Mysa may show options such as Low, Medium, High, and Auto Fan Speeds. Auto Fan Speed will follow settings in the Fan Coil Settings menu under Device Settings > Thermostat Configuration.

If your system only supports single-speed fan control, speed options may not appear.

Matter and Smart Home Integrations

Matter support may vary by platform and by which features each platform chooses to display. Mysa supports core thermostat controls through Matter, such as temperature, setpoints, and thermostat modes.

Advanced fan features—such as Minimum Fan Runtime Per Hour, and fan-only controls—may not be available in Matter or may not appear in every Matter-enabled platform. For the full set of fan settings, use the Mysa app.

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

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