What’s the Difference Between My Furnace Fan Settings—ON and AUTO?

There are furnace-fan settings on your thermostat for ON and AUTO. Which option is the best choice? There are devotees of both settings, each believing their setting is the optimum one to choose. 

But in reality, it’s more of a pros-and-cons type of situation. It really depends on which benefits are a priority for you. If you need help making the decision, call our Coastal Air + Refrigeration team in Carolina Forest and talk with one of our knowledgeable professionals.

What’s the Difference?

If you have your thermostat’s furnace fan (or air-conditioning fan for that matter) set to ON , the fan will continuously run, regardless if your furnace is running through a heating cycle, i.e., whenever your furnace is actually producing heat. 

If you have your furnace fan (again, or air-conditioning fan) set to AUTO , your system’s fan will run during the furnace’s heating cycle only. When your system reaches the temperature you’ve set for it, the fan will shut off until the next cycle.

Upside of Each

Here are the pros of each choice:

ON option

• Air is always being cycled through your furnace filtration system when your fan is continuously running. The result is increase indoor air quality , since particles are constantly being removed from your air.
  
• Keeping the fan running also means heating is more evenly distributed throughout your South Carolina home. No pockets of hot and cold. This also improves the reliability and life span of your system due to decreased starts and stops, somewhat like a car with highway or city driving. Less wear and tear.

AUTO option

• Since the fan only runs when the system tells it to and at the slowest speed necessary for heating, it’s consuming less energy than the ON option. This translates to decreased energy costs and less money spent by you. Your furnace filter will also last longer, since air isn’t being pushed through it as much.

Downside of Each

Here are the cons of each choice:

ON option

• The biggest con to having your fan continually running is the cost involved. It’s going to be expensive (unless you have a variable speed motor), much more than it would be on the AUTO option. 
  This downside may not affect you as much if you purchase a new system after July 2019. According to the online heating, ventilation, air conditioning, and refrigeration (HVACR) magazine, The ACHR News , the US Department of Energy (DOE) requires heating, ventilation, and air conditioning (HVAC) manufacturers to comply with the DOE’s new energy conservation standards for residential furnace fans starting July 3, 2019. They predict it will, among other things, save Americans more than $9 billion in home electricity bills through 2030. So if you like the ON option and your furnace is getting older, purchasing a new system now may save you money in the long run.
• Another downside of the ON option is you’re going to be replacing your furnace filter more frequently, since your air is being continually cleaned.
• Also, in the winter, you may feel a little cold from time to time. Since the fan is running even when the furnace isn’t running through a heat cycle, cold air will be blowing through your vents during that time.

AUTO option

• With this option, since there are more starts and stops, there will be more wear and tear on the furnace. With all these starts and stops, there’s also less even distribution of heat. Once the furnace stops, the air is no longer being moved around, resulting in cold spots. Also, since your air isn’t being filtrated 24/7, your home’s air isn’t as clean.