Setting Your AC Fan To Run

Stacy CookMold Issues

Setting your AC fan on “Run” instead of “Auto” will cause mold. See why. 


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During the warm season, homeowners usually keep their air conditioning units working around the clock to maintain a comfortable indoor temperature. One of the AC settings that people commonly use is “auto fan mode,” which turns on the fan only when the cool air is needed. However, some homeowners prefer to set their AC thermostat fans to “on mode,” which runs the fan constantly, even when the AC unit is not actively cooling the air. While it may provide some benefits, such as circulating the air and improving indoor air quality, it can also have some downsides that homeowners should be aware of.

The primary issue with running your AC thermostat fan constantly is that it can create a suitable environment for surface mold to develop. Mold is a type of fungus that thrives in moist and humid areas that lack good air circulation. When the air conditioner fan runs constantly, it continuously circulates air in the house, creating a high humidity environment that may encourage mold growth on the cool surfaces, such as walls, ceilings, and floors.

Moreover, the constant circulation of air increases the likelihood of condensation and moisture buildup on surfaces, especially if the home has poor ventilation or other moisture sources like leaky pipes. Mold spores can float in the air, and if they land on damp surfaces, they can attach, grow, and spread rapidly, creating a health hazard for residents. Mold can cause several health problems, including respiratory issues, allergies, and skin irritation.

To prevent surface mold growth in your home caused by running your AC thermostat fan constantly, it’s crucial to keep humidity levels in check. Use a hygrometer to measure the humidity levels, and ensure it is between 30% and 50%. Keep your home well ventilated by opening windows, adding exhaust fans in rooms that have water sources or running your AC fan on auto mode. Additionally, clean and replace air filters regularly and schedule annual inspections and maintenance for your AC unit to ensure it’s in good working condition.

While having your AC thermostat fan set to run constantly may seem like a good idea, it can have some negative consequences like surface mold growth. If you notice any signs of mold development, such as a musty odor, black spots, or discoloration on walls or ceilings, take action immediately to address the issue and prevent it from spreading. Remember to keep your home well ventilated, maintain good hygiene practices, and ensure your AC unit is in optimal working condition.