February 3, 2020
Mold – Why Setting Your Fan to On is Dangerous
How Setting Your Thermostat Fan to On Can Grow Mold by iMold in Fort Myers

Mold – Why Setting Your to ON is Dangerous

Are you aware that through one setting on your thermostat, you can cause mold to grow in your home? In Southwest Florida, an HVAC system is a vital part of day to day living. Humidity and temperature spikes are a constant battle for our residents. Many people try to beat the heat by staying indoors and running their AC set to different settings. Often times they will set their ACs with the fan turned on.
However, dust mites and mold love the thermostat fan. You should never leave a thermostat in the “on” position for longer than a day at a time for this reason. It doesn’t take long for mold to get out of hand here in Fort Myers and throughout Southwest Florida. Our humid weather is the perfect breeding ground for mold to grow.


Taking a look at your thermostat, you will find the fan settings. The two settings for a fan are “on” and “auto.” Using the ON setting will cause the air conditioner fan to run 24/7. This will not tell you whether the AC fan is cooling the air or not. The AUTO setting will run the fan only during the cooling cycles and will shut the fan off between.
Leaving your fan on the ON setting will bring about undesirable outcomes. The first, your energy bill will increase. Nobody enjoys paying more than necessary for their energy bill. Leaving the fan on will create a constant flow of energy. Your power use will increase and place an extra 200 hours per month on your bill.  Just like any other device that runs constantly, it will wear out faster. Maintenance or a complete replacement may be necessary sooner than if you had left the fan set to the auto position.

Thermostat Fans and Humidity Battles

If the fan is set to the ON position daily, your home will be unable to rid itself of humidity. This, unfortunately, results in dust mites and mold growth. The EPA suggests an indoor humidity level for your home to be between 30%-50%. These levels prevent dust mite and mold breeding from occurring. When a thermostat fan is set to ON, mixed with our high humidity, the indoor humidity level tends to rise to around 70%. With a humidity level this high, mold and dust mite growth become a serious inevitability.
The science behind the humidity levels lies within the coils of the HVAC units. Water vapor begins to condense on the warming coils of the AC unit. In some cases, this water vapor can collect up to one to two pints in volume within the fins of the air conditioner. When the fan is running, this water vapor is being picked up and pushed back into the house. As a result, you experience increased indoor humidity levels.

Mold and Dust Mites

While indoor humidity levels may not seem like a problem, the results are home and health damage. This ultimately takes a toll on the owner, other residents, and pets too. Mold thrives in moisture. High humidity levels are the perfect environment for mold to breed. When mold is in your HVAC system, you’ll experience health symptoms long before ever seeing it. Sinus congestion, sneezing, coughing, and even a decrease in cognitive function are all related to mold exposure. Read our blog for more information concerning the negative health consequences of mold by clicking here.
When the mold grows in the ventilation system, the spores become airborne quickly. This also means they become inhaled with ease. Those with asthma or COPD will feel an increase in flare-ups as the mycotoxins enter their lungs. Pets may also suffer and show signs like those in humans when exposed to mold. Pet food or water that has been sitting in a bowl for a lengthy time can also become affected by mold spores. Once this occurs, it becomes a health risk to your pet when ingested.
Dust mites, like mold, become attracted to and thrive in moist areas. When the humidity levels spike, dust mites breed. On surfaces, in bedding and upholstery, these cousins to the spider can take over rapidly. Children are five times more likely to develop asthma when exposed to dust mites.

What Can Be Done?

The best way to fight these undesirable issues is by controlling your humidity level. You should also stay on top of routine maintenance. Dust, and be sure to keep the thermostat fan on auto. If you have a home thermostat system that controls humidity levels, keep it between 30%-50%. This will decrease the chances of excessive moisture indoors. Finally, take advantage of iMold’s air duct cleaning services. Cleaning your ducts help reduce the amount of allergens and dust mites that are airborne. It also decreases the chances of mold spores from spreading.

We provide mold removal, remediation and water damage repair services throughout Southwest Florida. We service clients from Marco Island, all the way up to Port Charlotte. We’re excited to be expanding our service area into Sarasota very soon!
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Published: February 3, 2020
Author: iMold Author
Categories : Other