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Choosing between “Fan On” or “Auto” when setting your thermostat can have a dramatic effect on your comfort and energy usage. Both settings have benefits, though the “Auto” option tends to be the better choice in most cases.

The “Fan On” Option

Choosing this setting will keep the fan of your HVAC system running constantly between heating or cooling cycles. When running, the fan can use between 300 and 500 watts of electricity.


  • Better air circulation, which reduces hot or cold spots between cycles.
  • Constant air filtration, which improves indoor air quality and helps reduce allergy and asthma symptoms.
  • Less wear on the blower motor due to fewer stops and starts.


  • Higher energy usage because the fan is constantly running.
  • Reduced dehumidification. Any moisture left on the evaporator coils between cooling cycles can be evaporated again by the constant air movement.
  • Cool draft from air movement in the winter.
  • More frequent air filter changes.
The “Auto” Option

In this mode, the system fan only turns on as required by the HVAC system to distribute air.


  • Less energy usage because the fan is off between cycles.
  • Better humidity control. Moisture on the evaporator coil can drain between cooling cycles.
  • Air filters last longer.


  • Reduced air filtration due to intermittent airflow.
  • Less even distribution of heated or cooled air.
  • Increased wear on the blower motor.

With less energy usage and reduced humidity, setting your thermostat to “Auto” is better in the long run. But by manually running the fan for a short while after the heating or cooling cycle ends, you can enjoy some of the benefits of both options. These benefits include better air filtration, lower humidity and reduced energy usage.

Some programmable thermostats offer advanced fan controls to automate the process. Another option is to upgrade to an HVAC system featuring a variable-speed fan that can circulate air between cycles at a reduced speed, saving energy.

For more information about setting your thermostat properly, talk to our team at NisAir Air Conditioning and Heating. We serve Martin, Palm Beach and Indian River County.