Homeowner Articles Should I Leave My Furnace Fan On or Auto in Winter

Running your AC to produce cold air in the summer can be expensive, but heating your home during the chill of winter can be pricey as well.

Is there anything you can do this winter (besides suffering through the cold drafts) to reduce those energy bills? You might have wondered whether your thermostat’s “Automatic” setting might help.

Is there a difference between setting your furnace fan to “On” or “Auto” in winter? In short, yes, but it’s complicated. We’ll dive into the reasons why below.

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Moving Hot or Cold Air with the “On” Furnace Fan Setting

Smart Nest Thermostat

The “On” setting and the “Auto” setting work similarly on most thermostats. They’re close enough that, if you didn’t know there was a difference, you might not ever give it a second thought. The main discrepancy between the two is how the furnace fan in your HVAC system activates.

Benefits to the “On” Setting

When your furnace fan is set to “On,” that means you’re running the fan all the time, regardless of whether the heating system also runs or not. This is less energy efficient, but it also moves warm air through your house more consistently.

When the fan runs constantly like this, you may notice a few benefits that help offset higher utility bills. First, there may be fewer hot and cold spots around your home as the constantly circulating air heats things more evenly.

Second, you may notice better air quality by keeping the fan running constantly as it pushes more dirty air through your home’s air filters.

Finally, while you’ll have to deal with reduced energy efficiency, your furnace will also suffer less wear and tear. When the furnace fan constantly stops and starts, it can be hard on its motors.

The same principle applies to an air conditioner: stopping and starting it frequently will wear the system out faster.

Downsides to the “On” Setting

The main drawback of having your furnace fan set to “On” is the reduced energy efficiency. There’s no denying it—when you run your furnace fan constantly, it consumes more energy, which you’ll have to pay for.

However, you may end up paying more to replace your furnace filter frequently, too. When you’re running the fan constantly, you will enjoy cleaner air, but only if the filter itself is clean.

Because said filter will be constantly running to clean more air, you’ll need to replace it more often.

Additionally, some heating and cooling systems could end up pumping freezing air through your home, even in the middle of winter!

If the furnace takes too long to turn on, your furnace fan will just blow the air inside your home around, whether it’s warm or not.

Saving Energy with the “Auto” Furnace Fan Setting

Furnace Fan set to on

Whether you need warm or cool air, the “Automatic” setting on your thermostat can add up to significant savings throughout the year.

However, depending on what you need from your home heating system, these lower costs might not balance out all the drawbacks.

Benefits to the “Auto” Setting

When you set your furnace fan to “Auto,” your thermostat will decide when to turn the fan on or off. It will do this based on the air temperature inside your home and your chosen thermostat settings. Usually, the fan will only activate when your furnace also turns on to heat your home.

The “Auto” furnace fan setting will save you some money on your heating and cooling bills.

Because you won’t have your fan running constantly, your air filter won’t need replacement as often, either.

These energy savings and filter savings add up throughout the year, making “Auto” surprisingly cost-effective.

This is especially true if you have a recent smart thermostat. Today’s smart thermostats with “Auto” settings are even better at knowing when to heat when to cool, and when to turn on the fan.

Downsides to the “Auto” Setting

The cost savings provided by the “Auto” furnace setting are offset by some drawbacks that you should be aware of. First, your furnace fan may experience more wear and tear over time.

However, the extra damage over a decade or so of use adds up slowly, as will become obvious to you when you have your HVAC inspected by a certified technician every year.

Second, you may notice a decrease in air quality. Since the fan will only activate when your furnace turns on to heat your home, the air may start to feel stagnant or stale.

The third downside is the presence of hot or cold spots. You may notice that the heat levels in parts of your home don’t always align with your desired temperature.

This is due to the way your furnace works and the decreased air distribution. You may need to set your temperature higher or lower than you expected to even out those drafty spots.

Should You Set Your Furnace Fan to “On” or “Auto” in Winter?

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Whether you set your furnace fan to “On” or “Auto” in winter depends on what matters most to you. With typical use, “Auto” will indeed save money. However, if you live in a smaller home, the cost savings could be small enough to ignore in favor of other benefits.

Regardless of which option you choose, it’s always wise to have your furnace inspected yearly for optimal performance.

If you need an HVAC repair, inspection, UV light system, smart thermostat, or anything else furnace-related, don’t hesitate to contact Upstate Home Maintenance Services for help. Call us at (864) 529-7310.

This article was written by Morgan Loch

Owner of Upstate Home Maintenance Services LLC and Local HVAC Guru

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