Understanding Fan ControlUpdated 12 hours ago
Mysa for Central HVAC gives you flexible control over how and when your system’s fan runs. Depending on your HVAC system’s wiring and configuration, the fan may be controlled directly by the thermostat or automatically by the HVAC system itself.
This article explains the different fan behaviors you may encounter, including Fan Only Mode and Minimum Fan Runtime.
Thermostat Fan Control vs. System Fan Control
Your fan behavior depends on the wiring and configuration code of your Mysa thermostat.
System-Controlled Fan
If you do not have a G-wire (typically configuration codes ending in A*):
The HVAC system controls the fan automatically.
The fan runs only when heating or cooling is required.
Fan settings will not be visible 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 through the G-wire.
Fan settings such as Fan Only Mode and Minimum Fan Runtime will be available.
Tip: You can check your configuration code in the Mysa app under
Device Settings → Thermostat Configuration.
Fan Only Mode
Available for thermostat-controlled fan systems
Fan Only Mode runs the fan continuously, without activating heating or cooling. This is useful for improving air circulation, comfort, and filtration.
How Fan Only Mode Works
When selected, the fan turns on immediately and stays on.
Heating and cooling do not run during this mode.
To stop it, select another mode (Heat, Cool, Auto, Aux/Emergency, Off).
If your system lacks a G-wire, this 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 the mode.
Select Fan Only Mode.
Minimum Fan Runtime
Available for thermostat-controlled fan systems
Minimum Fan Runtime lets you set a minimum number of minutes per hour the fan should run — even when heating or cooling isn’t active.
Available Settings
0 minutes (default) – Fan runs only during heating/cooling cycles.
15 minutes per hour
30 minutes per hour
45 minutes per hour
60 minutes per hour – Fan runs continuously.
How It Works
If you select 30 minutes per hour:
Suppose the fan runs for 10 minutes during heating/cooling.
Mysa will run the fan for an additional 20 minutes in that hour.
Mysa spreads this runtime evenly, adjusting based on system needs.
The fan may run even in Off mode to meet your selected runtime.
How to Set It
Tap the device tile in the Mysa app.
Go to Settings > Thermostat Preferences.
Scroll to Minimum Fan Runtime.
Choose your desired duration.
Key Benefits of Fan Control
Improved Air Quality
Circulates and filters air continuously, reducing dust, allergens, and pollutants.Enhanced Comfort
Helps eliminate hot or cold spots by distributing air evenly across rooms.Energy Efficiency
Supports more stable indoor temperatures and reduces the frequency of full heating/cooling cycles.Humidity Control
Aids in regulating moisture levels by preventing buildup, especially in humid climates.