What fan settings should I be using on my thermostat?

There are many great questions that we are forced to examine throughout our lives, one of those questions, is the AUTO vs. On feature for our fan setting on our thermostat.  What do the features even mean, which setting should I use, why?  Here at Halo Home Watch many of our clients in Southwest Florida (Bonita Springs, Estero, Marco Island) are from all over the country and even the world, but they usually share one thing in common, they all hail from a colder climate.  This is important because as we will discuss, climate matters, and will affect the choice we make. What we do up north is not the same as here in Naples or Marco Island. 

What is the difference between On and Auto on a thermostat?

Air conditioners have two responsibilities, cooling and dehumidifying. The part of the AC that cools is adjusted by changing the temperature setting on your thermostat, while air circulation is controlled by setting the fan to AUTO or ON.

Knowing what setting to use is essential to having your HVAC running at peak performance. Therefore, to properly set our thermostat we need to understand what these settings mean.

AUTO – means that the fan only turns on when your system is heating or cooling air. Once the thermostat reaches the desired temperature, the blower fan will shut off until next cycle.

ON – means that the blower fan is continuously running, circulating air even when your HVAC is no longer heating or cooling.

What are the benefits of setting my fan to ON?

For most snowbirds up north, using the ON setting can provide some great benefits.  The two most important benefits are:

Temperature Uniformity – Continuously circulating air throughout the home is excellent for maintaining uniform temperature across the entire house.  This is great for multi-storied wood-framed houses which are typically found up north. (Nothing is worse than someone raising the temperature on the ground floor because they are freezing while upstairs you are melting away.)

Reducing Airborne Pollutants and Allergens – Those who suffer from allergies may also notice differences when the fan is set to ON.  The air filter only works when the blower fan is on and the filter is what helps remove all of the pollutants and allergens in the air so that we can breathe easy. 

Still, leaving the thermostat at the ON setting will come with its drawbacks. 

What are the negatives of setting my fan to ON?

Clogged Air Filter – Since the fan is constantly running it’s going to grab more dust in a shorter amount of time. This will require you to change your air filter more frequently than normal.

Increased Repair and Maintenance – Leaving the fan running constantly will also increase the risk of it breaking down and requiring maintenance.

Increased Electric Bill – leaving your fan on 24/7 has the potential to increase your electric bill anywhere from $40 – $80 a month on average.

Recirculates Humid Air – By running the fan after the coil warms up, the air does not have a chance to condense and the humid air is put right back into the home.  

The last of these issues being especially problematic in climates with high levels of humidity like Southwest Florida (Bonita Springs, Estero, Marco Island, and Naples). We will discuss this later in greater depth.

What is the main benefit of setting my fan to AUTO? 

The AUTO setting on a thermostat as we discussed, means that the fan only turns on when your system is heating or cooling the air in the home.  This enables the moisture from the air to condense on the cold evaporator coil and eventually drain out the condensate line.  (To learn just how important keeping your condensate line clean and unclogged is, view our blog on How to Clean My Condensate Line?

When the fan is constantly running, especially when the AC is no longer cooling and the coil is still warm, it does not give the moisture a chance to drain. This causes the moisture to evaporate again only to be pushed back throughout the home, leaving your household as humid as it was before and more susceptible to mold!

While there are several benefits to setting the fan to AUTO, its ability to lower the humidity in a home is its most important.

Should I set my thermostat to AUTO or ON? 

Humidity vs. Temperature Uniformity

Florida has the highest levels of humidity of any state in the U.S.  In fact, southwest Florida has nine months out of the year where the average relative humidity is above 55%, which also unfortunately happens to be the starting point for mold growth!

Most of the homes in southwest Florida are single story and made from concrete instead of wood-frame.  Houses made from concrete have a higher thermal point unlike wood-frame houses. This means that they maintain their temperature better than the homes more commonly seen up north.  

Thus, temperature uniformity is a much lower concern than dealing with humidity.

Furthermore, 66% of the residents in Bonita Springs, Estero, Marco Island, or Naples are here only seasonally. Now reducing allergies or temperature uniformity may not matter when you are gone but preventing mold certainly still will!  

Know your Homeowner’s Insurance Policy

Most homeowner’s insurance policies will deny claims for mold issues related to humidity, even more so in a climate known to be excessively humid.  For example, claims are more likely to be rejected if mold is caused by neglected home maintenance, long-term exposure to humidity, or repeated water leaks and seepage.  Take an hour or two to review the language of your policy, especially as it pertains to water damage. Look for mold exclusions or limitations. Call your agent if the wording is unclear. (click here to learn more)

Caring for Your Home When You Are Away

Therefore, leaving the fan setting at ON can be extremely dangerous for seasonal homeowners.  As we discussed it keeps circulating moisture-laden air back into the house without giving it a chance to cool into condensation and drain through the condensate line. This means that the humidity will persist, and that humidity can lead to mold and that mold can cause unspeakable damage to your home.

Some would argue that you should always leave your fan setting on AUTO in this climate even when you are present as the negatives greatly overshadow any positives a homeowner can gain.  Therefore, if you are a seasonal homeowner, a snowbird, we recommend the following:

It is recommended in Southwest Florida to always leave your fan setting on AUTO to protect your home when you are away.

Closing Thoughts

At Halo Home Watch most of our clients are seasonal and we always recommend that they use a detailed end of season departure checklist to avoid forgetting anything on their way out the door, this includes their fan setting!  We provide a detailed checklist to every new client, which can be downloaded here.  

Remember, if you use a Home Watch Professional to check your home while you are away, part of their check should be to independently review the relative humidity in the home with a hygrometer and review the operability of your thermostat.  A great interview question when considering a Home Watch company is to ask them whether the fan setting matters and what they recommend.   

Setting your fan to AUTO is one of the best things you can do to reduce humidity in your home, but it is not the only step.  To learn more about things you can do to reduce humidity in your home check out this article.  

Works Cited

Bailes, A. (2011, June 6). Don’t Set Your Air Conditioner Thermostat Like This. Retrieved from Energy Vanguard: https://www.energyvanguard.com/blog/38619/Don-t-Set-Your-Air-Conditioner-Thermostat-Like-This

Caughill, & Daniel. (2020, March 19). ValuePenguin. Retrieved from When Your Insurance Will (and Won’t) Cover Mold Damage: https://www.valuepenguin.com/does-homeowners-insurance-cover-mold

Home Insurance and Mold: Is Mold Covered? (n.d.). Retrieved from houselogic: https://www.houselogic.com/finances-taxes/home-insurance/homeowners-insurance-mold-covered/

Materson, & Les. (2019, June 20). Is mold covered by insurance? Retrieved from insurance.com: https://www.insurance.com/home-and-renters-insurance/home-insurance-basics/mold-coverage.html

ON VS. AUTO: Which Thermostat Setting Is Better? (2015, August 4). Retrieved from Cool Today: https://www.cooltoday.com/blog/on-vs.-auto-which-thermostat-setting-is-better-for-your-home

Should I Set my HVAC System’s Fan Setting to Auto or On? (n.d.). Retrieved from Rhoads Energy: https://www.rhoadsenergy.com/should-i-set-my-hvac-systems-fan-setting-to-auto-or-on/

Should You Run Your Blower Fan without the Air Conditioner? (n.d.). Retrieved from And Servcies: https://www.andservices.com/blog/run-blower-fan-without-air-conditioner/