Setting Your Thermostat: Should You Turn the Fan to On or Auto?

“Cool” and “heat” are perhaps the modes most used on a thermostat. The “on” and “auto” fan settings have useful functions, but are perhaps more confusing. Using the thermostat correctly can have a significant impact on home comfort and on savings on energy bills in Northern Virginia. The following tips can be used as a guide for setting your thermostat, and understanding HVAC system efficiency.

Fan Mode Basics

A thermostat controls the two basic functions of an air conditioner: cooling and airflow. Cooling is regulated by the thermostat temperature setting. Airflow is controlled by the fan modes “on” and “auto.” When the fan is in “on” mode, the air conditioner’s fan runs continuously. In “auto,” the fan turns on and off in sync with the cooling components.

Deciding Between “On” and “Auto”

Both thermostat settings have advantages and disadvantages.

• Energy efficiency – If the thermostat is set to “on,” the fan will run continuously, consuming more of your energy dollars.

• Dehumidification and comfort – Dehumidification is an incidental effect of the cooling process. Humidity in the air condenses on the evaporator coil and is removed from the living spaces. If the air conditioner is set to the “on” position, the continued airflow will simply evaporate the condensation before it can drip and drain away, resulting in indoor air that is too dry for comfort. “Auto” wins for better dehumidification.

• Indoor air quality – In the the “on” mode, air continuously circulates through the air filter. This will remove more airborne contaminants than “auto,” leading to better indoor air quality.

• HVAC wear and tear – The “on” position runs the blower motor more frequently, resulting in more wear and tear. However, with routine, and professional preventive maintenance, this may not be an issue.

Overall, you may be better served by using the “auto” mode more often for better dehumidification and lower energy bills. Additionally, use your ceiling fans to improve air movement and enjoy greater energy savings.

For more information about using and setting your thermostat for increased energy efficiency, contact Brennan’s Heating & Air Conditioning at (703)763-0399. We have been providing reliable and expert service to Woodbridge and the surrounding areas since 1979.

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