Should I Set My Thermostat to AUTO or ON?

HVAC Logo IconBy Tom MoorDecember 22, 2023

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Woman adjusting the thermostat

The ongoing debate between setting your thermostat to “AUTO” or “ON” is a common dilemma for many homeowners looking to optimize their HVAC system. The decision hinges on the choice between the fan’s two operating modes: AUTO and ON. There are benefits and drawbacks of both options – HVAC.com explains how using the AUTO vs ON setting on your thermostat compares when it comes to energy efficiency, indoor air quality, and more.

What Do the Fan AUTO Vs. ON Settings Mean?

The thermostat AUTO vs. ON settings dictate how the HVAC system’s fan operates. When set to AUTO, the fan runs only when the heating or cooling system is actively regulating the temperature. In this mode, the fan automatically turns off once the desired temperature is achieved, promoting energy efficiency by minimizing unnecessary operation. On the other hand, selecting ON means the fan runs continuously, regardless of whether the heating or cooling system is actively engaged.

Energy-Efficiency Considerations

One of the primary factors to consider when deciding between using the thermostat AUTO vs ON settings is energy efficiency. The AUTO setting is generally more energy efficient since the fan operates only when necessary. Because it turns off automatically when the desired temperature is reached, this setting conserves energy and reduces utility costs. On the flip side, setting the fan to ON may result in higher energy consumption as it runs continuously.

Comfort and Indoor Air Quality

While energy efficiency is a crucial consideration, comfort and indoor air quality also play a significant role in the decision-making process. The continuous operation of the fan in the ON setting can help distribute air more evenly throughout the home, reducing hot and cold spots. Additionally, it can enhance air filtration by continuously circulating and filtering air through the HVAC system’s filter, promoting a healthier indoor environment.

However, some homeowners may find the constant circulation of air less comfortable, especially during periods when the heating or cooling system is not actively in use. This is where the AUTO setting shines, providing a quieter and less intrusive operation during idle times.

Humidity Control

Another critical factor to consider is humidity control. The AUTO setting can be more effective in managing humidity levels, especially in humid climates. When the thermostat triggers the HVAC system to run, the AUTO setting ensures that the fan operates long enough to remove excess moisture from the air, while turning off the HVAC system to allow moisture to drain from the coils and exit the unit. This helps prevent the growth of mold and mildew, contributing to a more comfortable and healthier living space.

Conversely, the ON setting may not be as effective in humidity control since the fan runs continuously. When there is no break in air circulation, the moisture from the coils can cycle back into your home, leading to more humidity in the indoor air.

System Wear and Tear

The choice between using the thermostat AUTO vs ON settings also has implications for the wear and tear on your HVAC system. While allowing the fan to rest during periods of inactivity, the AUTO setting can potentially extend the lifespan of the fan motor and other components. Running the fan continuously in the ON setting keeps the fan operating over longer periods, increasing the rate of wear on the blower components.

Thermostat AUTO Vs ON: Which Setting Should You Choose?

In the end, the decision to set your thermostat to AUTO or ON boils down to a balance between energy efficiency, comfort, air quality, humidity control, and system longevity. Each setting has its advantages and drawbacks, and the ideal choice may vary based on individual preferences, climate conditions, and the specific HVAC system in use.

For those seeking the optimal blend of energy efficiency and comfort, the AUTO setting is generally recommended. It ensures the fan operates only when necessary, conserving energy and providing a quieter indoor environment during periods of inactivity.


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