On or Auto: Which is the Better Thermostat Setting for Your Facility?

Keeping your facility warm or cool requires a constant interaction between the thermostat and the indoor environment. There are times, however, when you may not require the full capabilities of your HVAC system, such as when temperatures are relatively mild in the spring and fall. During these periods, a thermostat setting that provides for fan-only operation may be sufficient to maintain your facility at a comfortable temperature.

Your thermostat should offer you a choice: turning on the fan and leaving it on or running it via an automatic setting that turns it off or on in response to signals from the thermostat. Whether you use “on” or “auto: as a thermostat setting depends on what you want to accomplish when your heating or cooling system operates.

What the Fan Does

The fan is an essential component of your forced-air heating or cooling system. The fan is what actually moves the air and “forces” it through the system.

In response to the thermostat setting, your furnace, air conditioner, or heat pump will create heated or cooled air. The fan then forces that air into the ductwork, pushing it down the length of these air distribution pipes. The heated or cooled air exits through vents at the ends of the ductwork, entering your facility and making your indoor spaces warmer or cooler. When the room is warm or cool enough according to the thermostat setting, the fan kicks off and stops distributing air. When the temperature rises or falls enough, the cycle will begin again.

When you turn the fan to “on,” it will run constantly whatever the temperature and whether or not your need more heating or cooling. When you turn it to “auto,” it will operate only when needed to distribute air and provide temperature control for the interior of your facility.

Fan Always On

• Advantages: A fan that is always on will provide a steady flow of air through your heating or cooling system. This will increase indoor ventilation and provide a steady stream of milder-temperature air. It ensures that your indoor air is always being circulated through the air filters, removing particulates and improving indoor air quality. By running consistently without multiple starts and stops, the fan will also last longer since it won’t wear out as quickly. Finally, a fan that is always on will distribute heating and cooling more consistently and evenly.
• Disadvantages: A fan that is always on will consume more energy than one that is allowed to turn off when it’s not needed. Your monthly energy bills will be noticeably higher. Your air filters are likely to get dirty faster, though this is not a significant disadvantage since it indicates that your indoor air is still being cleaned. Air moving through the system will affect indoor comfort level by, for example, circulating cooler air in the winter.

Fan Set to Auto

• Advantages: Using the auto setting on your HVAC system fan means that it shuts off when it’s not needed, saving energy and money. Air filters will not get dirty as quickly.
• Disadvantages: Fans that stop and start regularly will experience more wear during this process than fans that run consistently. Distribution of heated and cooled air is not as effective or consistent, which could affect indoor temperatures and comfort levels.

A Potential Solution

One way to get the most efficient operation out of your HVAC system’s fan without the high energy consumption is by installing a variable-speed fan. Variable-speed fans, or blowers, can run at a lower level that provides plenty of ventilation and air circulation while also consuming less energy.

Our goal is to help educate our customers about Plumbing, HVACR, Fire Protection, and Alarm Systems in Mechanical, Commercial, and Residential settings. For more information on the best thermostat setting and fan position for your commercial facility or office building, or to view projects we’ve worked on, visit our website!

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