As more and more people look to cut down their electric bill for both monetary and environmental reasons, you may be asking “should I run my furnace fan continuously?” Below, we take a look at your options with a focus on two key elements: comfort and cost.

Benefits and Drawbacks of Keeping Your Furnace Fan On

From allergy control to humidity, there are multiple factors to consider when weighing whether to keep your furnace fan running continuously. The list below will provide pros and cons of keeping your furnace fan running throughout the year, as well as a few instances where you may want to consider keeping your furnace set to automatic rather than leaving it running all the time.

Pros of Keeping Your Furnace Fan On Continuously

While setting the furnace from “On” to “Automatic” may seem more energy efficient, doing so may raise your bill rather than lower it. Most experts tend to agree that leaving it on is a better option, but there are cases for both settings. In particular, you may want to keep it running if:

  • People are at home for most of the day
  • You or anyone in your family suffer from allergies or respiratory problems
  • Some rooms in your home are noticeably warmer than others

From more even temperature distribution to allergy control, there may be several ways having your furnace fan on may benefit your home. 

  • Better Temperature Distribution – Keeping your furnace fan running continuously throughout the day will better regulate the temperature of your home. Rooms that might get hotter during the day will experience less fluctuation, making it ideally suited for multi-story homes where heat tends to rise.
  • Allergy Control – Do you suffer from seasonal allergies? Running over to the drug store isn’t the only way to alleviate sinuses. Keeping your fan on during the spring and summer can help reduce symptoms with constant circulation. That’s because homes with circulating air tend to have better air quality and better dispersed allergens.
  • Lower Heating and Cooling Costs – It may sound counterintuitive that running a fan all day would lower your electricity bill, but it can often be the case—provided that you have a newer furnace installed. Running a fan throughout the day is inexpensive—much lower than the cost of running an AC unit alone—and using both in conjunction with each other means that you won’t have to keep your air conditioning running all day.

Air conditioning can run you hundreds of dollars every month to cool your home, while running a fan in that same time frame costs about as much as a large cup of coffee. Cool air can circulate around your home evenly, without racking up a hefty bill.

Cons of Keeping Your Furnace Fan On Continuously

While there are certain benefits to keeping your furnace fan, a few additional factors might incline you to turning the fan off more often.

  • Humidity – If you have an oversized cooling system, humidity may become an issue when keeping the fan on for extended periods of time. Moisture from the air tends to condense on an AC unit’s evaporator coil—when a fan is not shut off, this moisture gets pushed back into your home, resulting in increased humidity indoors.  
  • Inefficient Fans Can Spike Energy Bills – Earlier iterations of furnace fans tend to be less energy efficient. Furnaces tend to last between 15-30 years, meaning older models are equipped with fans that weren’t intended for constant use. However, as these models are being phased out, this is becoming less of a problem for most homeowners.
    Variable speed motors provide the greatest energy savings, while older models do not. If cost is your primary concern, this must be taken into consideration.
  • Filter Must Be Changed More Frequently – With more air flowing through your home, your filter will be collecting more pollen and dust that would normally remain stagnant in your home. While this is good for indoor air quality and allergy control, keeping the fan on continuously will require more frequent replacements of furnace filters.

Should I Keep My Furnace Fan on Automatic?

There has been some debate over whether running a fan continuously increases or decreases the need for maintenance. Like any motor, stopping and starting a fan tends to put more wear and tear on it than if you keep it running constantly. For this reason, most experts seem to agree that running a furnace on automatic does more harm than good to a furnace fan.

However, there are a few cases where it may be more advisable to keep your fan setting on automatic:

  • If Your HVAC System is Located in the Attic – Today’s homebuilders avoid placing HVAC systems in the attic, and for good reason. Temperatures in an attic can get up to 140 degrees in the summer months, meaning your air conditioning will be working overtime pushing hot air into your home. This increases cooling costs and decreases efficiency.
  • Your Home Has Old HVAC Equipment – Advances in technology have made air conditioning systems exponentially more cost-effective and energy efficient. If you have an older furnace fan installed, leaving it on all day may raise your energy bill rather than lower it.
  • Leaky Ductwork – Homes built after 2015 are now all required to have their ductwork tested for air tightness. In older homes, this can pose an issue. Most homes lose about 20% of their cooling due to poorly connected ducts, meaning a fan that is blowing all the time will not be as effective.

In all of the scenarios posed above, switching your furnace fan to automatic may be advisable. However, these problems also hint at greater problems with your HVAC system, and should be inspected by an HVAC company or experts to lower your cooling costs.

Making the Call

If you have a newer furnace, it’s actually best to leave your furnace running continuously rather than setting it to automatic. You may have to change your furnace filter more frequently, but your AC unit won’t have to run as much thanks to evenly distributed cool air throughout your home. Your home will be more comfortable, and you will be paying less money over time.

Older furnaces don’t have the same efficiencies that newer ones have, so an automatic setting may be the better call in these situations. But you may want to consider the age of your furnace and whether it is time to replace it.

If your furnace and AC is older, or you’re having issues with your HVAC system, opting to switch it to automatic only presents a temporary solution to lowering costs. Experts like Simpson Sheet Metal have the tools and know-how to assist with HVAC service and repair. Contact us today for inspections, preventative maintenance, and more!



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Premier Heating and Cooling. Furnace Fan Setting: On vs Auto