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Setting the Thermostat: Fan On or Auto?

Setting the Thermostat: Fan On or Auto?In addition to designating a comfortable temperature, setting the thermostat involves making a choice about air circulation. Air movement is an important air conditioning function whether the primary cooling components—the compressor and coils—are operating or not. Anytime the system fan is running, over 1,000 cubic feet of air is circulating every minute through the ductwork.

Depending on the thermostat setting, the fan operates in one of two modes:

  • When set to “Auto” mode, fan function conforms to the cooling function. As long as the compressor and coils are operating, the fan is circulating cooled air. When the desired temperature setting is achieved and the cooling components cycle off, the fan stops and all air circulation ceases.
  • When the thermostat setting is in “Fan” mode, the fan circulates air all the time, regardless of whether the system’s cooling components are cycled on or off.

What Difference Does It Make?

Setting the thermostat in the “Fan” mode can be costly and less energy efficient. Many homeowners are unaware that a conventional permanent split capacitor blower motor alone consumes over 500 watts of electricity in cooling mode. When running 24/7, the costs therefore mount quickly.

Continuous fan operation can also affect home comfort. When the central air unit cycles off, condensation accumulates on the evaporator coil. If the fan keeps running even after the cooling system cycles off, it disperses water vapor from excess condensation into living spaces, raising household humidity and decreasing comfort.

Are There Any Exceptions?

In an arid climate where extra humidity added to the air will not impact comfort, running the fan for short intervals after the A/C cycles off can actually add more coolness to rooms in the form of water vapor in the air. However, for efficient continuous air circulation, consider upgrading to a variable-speed blower motor with ECM technology that uses only about 75 watts of electricity.

For more on setting the thermostat for comfort and efficiency in Fresno, contact Donald P. Dick Air Conditioning.

Our goal is to help educate our customers in the greater Fresno, California area about energy and home comfort issues (specific to HVAC systems). For more information about thermostats and other HVAC topics, download our free Home Comfort Resource guide.

Credit/Copyright Attribution: “Heymo/Shutterstock”