Your Thermostat: Fan On? or Auto?


Take a moment and look at your thermostat's digital display. Under "fan" it probably has two choices: "on" and "auto." It's important to understand the meaning of these two options, since whichever you choose when setting your thermostat could have a big effect on energy efficiency and home comfort.

What's the Difference?

Forced-air HVAC systems have two main operational phases: the phase that creates the cool or warm air and the air circulation phase in which the blower or air handler system pushes air through the house via ductwork. The fan setting on the thermostat mainly affects the second phase. If the "on" setting has been selected (or "fan only" on some thermostats), the fan runs 24/7, whether the cooling or heating equipment is operating or not. When switched to "auto," the fan only operates during heating and cooling. This is the default setting for most thermostats.

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Why "Auto" Is Usually Better

While some HVAC experts will recommend employing the "on" setting in certain circumstances, "auto" is usually the preferred setting. That's the case for several reasons, including the following:

  • The "on" setting may lead to higher humidity in your home if you have an oversized A/C, which is common in American homes. An A/C that's too big will tend to cycle on and off frequently. When the fan continues to operate when the air conditioning isn't running, it will blow air across the damp evaporator coil. This re-circulates moisture into the air that a continuously operating A/C would have evaporated from the surface of the coils.
  • Continuous fan operation, even during down time for the A/C and furnace, expends energy unnecessarily.
  • Many home occupants prefer occasional spans of silence to the constant whirring of an always-running HVAC fan.
  • If your ductwork has leaks, constant "on" fan operation will translate into more air lost to duct leaks, as well as dirty air infiltrating ducts and mixing with household air. 

For more advice on setting your thermostat, please contact us at Pipe Works Services. We proudly serve northern New Jersey with reliability and excellence.


Pipe Works Services gives advice on ways to make your home healthier and energy efficient.

The opinions expressed herein are the writer's alone, and do not reflect the opinions of or anyone who works for is not responsible for the accuracy of any of the information supplied by the writer.

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