Whether to keep the fan on while the AC is also on depends on the specific setup and the type of AC system you have. Here are a few scenarios to consider:
Central Air Conditioning System with Fan Setting: Many central AC systems have a "fan" setting that can be set to "Auto" or "On." If you choose "Auto," the fan will only run when the AC is actively cooling the air. If you choose "On," the fan will run continuously, even when the AC is not actively cooling. In this case, it's generally more energy-efficient to set the fan to "Auto" so that it only runs when needed.
Window or Portable AC Units: Some window or portable AC units have a separate fan setting. Similar to the central AC system, it's best to use the "Auto" setting for the fan to save energy and allow it to run only when the cooling is necessary.
Box Fans or Ceiling Fans: If you have separate fans, like box fans or ceiling fans, they can be used in conjunction with the AC to help circulate the cooled air throughout the room. Fans create a wind-chill effect that makes you feel cooler, allowing you to raise the thermostat setting on the AC and save energy.
Multi-Zone AC Systems: In some cases, there might be multiple AC units or zones in a home or building. In such setups, it's possible to have some zones with the fan on "Auto" and others with the fan on to provide continuous airflow in specific areas.
Humidity Considerations: In humid climates, keeping the fan on can help reduce humidity levels indoors. The continuous airflow helps prevent excess moisture buildup, which can make the air feel more comfortable even at slightly higher temperatures.
In summary, if your AC system has a "fan" setting, using the "Auto" option is generally more energy-efficient. However, you can use additional fans strategically to help distribute cool air throughout the space and create a more comfortable environment. Additionally, in humid conditions, having the fan on can assist in controlling indoor humidity levels. If you have specific concerns about your setup or energy usage, consulting with an HVAC professional might be helpful.