The Pros and Cons of Continuously Running Your HVAC Fan

By: Brian Schutt  |  April 21, 2021

“Should I set my HVAC fan to auto or on” is a question we commonly receive from Homesense customers — along with “does running the fan on my air conditioner use a lot of electricity?” It’s a debated topic throughout the industry, so we’re going to give you the pros, the cons, and our recommendation to avoid costly ac repairs and furnace repairs.

Setting Your HVAC Fan to “ON”

When you set your fan to “ON,” you’re telling it to keep running 24 hours a day, 7 days a week, regardless of the heating or cooling setting. There are a few positives to this feature.

Pros to Running Fan on Air Conditioner Continuously:

  1. Keeping the fan on creates a more even distribution of heating and cooling, circulating the air if you have cold or hot spots in your house, like a bedroom above a garage.
  2. Less frequent starts and stops of the fan can reduce the stress from startup, and potentially help extend it’s lifespan.
  3. Leaving the fan on 24/7 ensures cleaner air, as the air is pulled through the filtration or UV light system. This can be better for people with allergies.

While keeping your fan on 24/7 may be more energy efficient, there are a few downsides to leaving your fan on all of the time:

Cons to Keeping Fan Continuously Running:

  1. It could cost you hundreds of dollars a year. The average unit has a 500 watt fan, which uses almost as much energy over the course of the year as a refrigerator, resulting in a $50/month bill.
  2. During the summer months, the ducts in your attic and close to your walls can fill with warm air, resulting in the fan blowing hot air into your house. Therefore, you may end up running your AC even more, to counterbalance the extra heat. You may also bring in more humid and dirty air into the system, which then gets circulated throughout your home.
  3. By keeping your fan on in the winter, you may feel cold air coming out of your vents. Although the air temperature will be similar to the space temperature, your house will feel cold.
  4. Your furnace filter will clog up quicker (even though that means it’s working), but you will have to adjust your filter more frequently.

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Setting Your HVAC Fan to “AUTO”

Your other option is to set your fan to AUTO, which means the fan runs when directed to by the unit. Here are the pros and cons to this approach:

Pros to Allowing Fan to as Needed:

  1. This option is much more cost effective, because you are using less energy. The fan’s “AUTO” setting works with your heating + cooling system, so your fan is running the least amount of time needed, at the slowest speed.
  2. Your furnace filter will last longer.
  3. Better dehumidification. When your fan is on “AUTO,” moisture is able to drip from the cold cooling coils and drain outside. When the fan is running 24/7, that moisture doesn’t have a chance to drip outside. Instead, it blows back into your house, and, as a result, your AC then has to work ever harder to suck that extra moisture out of the air.

Cons to Allowing Fan to as Needed:

  1. You may feel a less even distribution of heating and cooling, because once the thermostat is satisfied, the fan stops moving air to other spaces in the home.
  2. More frequent starts and stops will make the fan wear out faster.

AC FAN ON OR AUTO: Which HVAC Fan Setting Is Best?

When keeping your air conditioner fan on or auto, there’s no boilerplate recommendation that we make to home owners, because everyone has different needs. At Homesense owner Brian’s home, he has it set ON all day because he has young children that are home and he has allergies, so the improved comfort and air quality are benefits that outweigh the costs. Whereas our other owner, Jesse, sets his home to AUTO because he works away from home all day, and is more concerned with reduced operating costs.

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PRO TIP: Many newer thermostats will have a variable speed blower or “circulate” option, that allows you to set the fan on for a certain amount of time every hour. The blower will automatically run at different speeds, giving you the benefits of lower electrical bills and increased comfort.

If you have any other questions about your HVAC fan, send us a tweet! We’d love to hear from you.


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