On or Auto: Which is the Better Thermostat Setting?

On or Auto: Which is the Better Thermostat Setting?

Most HVAC systems have a thermostat setting for “on” and “auto” that control whether the fan inside the air handler runs just when the system does, or runs continuously. Each has its benefits based on specific circumstances and some conditions inside your home.

When to Run the Fan Continuously

Letting the fan run constantly is a good way to reduce the volume of airborne particulates, especially during high allergy seasons or you’re deep-cleaning the house. The fan pulls a high volume of air across the air filter for the air handler, and depending on the filter quality, will remove many of the irritating particles.

While you will have cleaner indoor air, you may have a higher noise level indoors, especially in rooms near the air handler. Another downside using the “on” thermostat setting is increased energy bills. Many of these fans use measurable amounts of electricity, and if you’re running the fan to move the air, you will save money by installing and using ceiling fans. They use a fraction of the power the blower motor does.

When to Use the Auto Setting

Under most circumstances, its best to set the thermostat to auto so that the fan runs only when your home needs conditioning. However, the air won’t be continually filtered and the particulate load will increase indoors. Rooms further from the air handler may not feel as comfortable, since the air will circulate for shorter periods.


Fortunately, options exist for your current or next HVAC system to manage indoor air quality and provide continuous air circulation and the comfort it delivers.

  • Whole-house air cleaners are available that attach to existing HVAC systems and quietly and efficiently trap many offending particulates.
  • Variable-speed HVAC systems have longer, quieter and more energy efficient running cycles and deliver even comfort throughout your home. Since their cycles are longer, they also provide greater air filtration.

The thermostat setting does make a difference in your health and the comfort of your home. If you’d like to learn more about your HVAC options, contact Aggressive Mechanical Contractors, proudly serving Monmouth homeowners.

Our goal is to help educate our customers in Monmouth County, New Jersey and surrounding areas about energy and home comfort issues (specific to HVAC systems). 

Credit/Copyright Attribution: “doomu/Shutterstock”

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